Welcome to Cambridge IGCSE Physics(0625) RBIS!
The Cambridge IGCSE Physics syllabus helps learners to understand the technological world in which they live, and take an informed interest in science and scientific developments. They learn about the basic principles of Physics through a mix of theoretical and practical studies. Learners also develop an understanding of the scientific skills essential for further study at Cambridge International A Level, skills which are useful in everyday life.
As they progress, learners gain an understanding of how science is studied and practised, and become aware that the results of scientific research can have both good and bad effects on individuals, communities and the environment.
As they progress, learners gain an understanding of how science is studied and practised, and become aware that the results of scientific research can have both good and bad effects on individuals, communities and the environment.
What is Physics?
Physics is a natural science based on experiments, measurements and mathematical analysis with the purpose of finding quantitative physical laws for everything from the nanoworld of the microcosmos to the planets, solar systems and galaxies that occupy the macrocosmos.
Physics is crucial to understanding the world around us, the world inside us, and the world beyond us. It is the most basic and fundamental science. Physics encompasses the study of the universe from the largest galaxies to the smallest subatomic particles. Moreover, it's the basis of many other sciences, including chemistry, oceanography, seismology, and astronomy. So--physics is interesting, it is relevant, and it can prepare you for great jobs in a wide variety of places. Shouldn't you take a physics course? |
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Why is physics so interesting?
Physics Syllabus 2019-2020
Year 1
Semester 1 Measurements and Motion 1. Measurements 2. Speed Velocity and acceleration 3. Graphs of equation 4. Falling bodies 5. Density Forces and Momentum 6. Weight and stretching 7. Adding forces 8. Forces and acceleration 9. Circular motion 10. Moments and levers 11. Center of mass 12. Momentum Energy, work, power and pressure 13. Energy transfer 14. Kinetic and potential enerygy 15. Enerygy sources 16. Pressure and liquid pressure Year 1 Semester 2 Simple Kinetic molecular model of matter 17. Molecules 18. The gas law Thermal properties and temperature 19. Expansion of solids, liquids and gases 20. Thermometers 21. Specific heat capacity 22. Specific latent heat Thermal Process 23. Conduction and convection 24. Radiation |
Year 2
Semester 1 Section 3 Properties of waves General wave properties 25 Mecganical waves Light 26 Light rays 27 Reflectiob of light 28 Plane mirrors 29 Refraction of light 30 Total internal reflection 31 Lenses 32 Electromagnetic radiation Sound 33 Sound waves Secton 4 Electricty and Magnetism Simple phenomena of magnetism 34 Magnetic fields Electrical quantities and circuits 35 Static electricity 36 Electric current 37 Potential difference 38 Resistance 39 Capacitors 40 Electric power 41 Electronic systems 42 Digital Electronics Electromagnetic effects 43 Generators 44 Transformers 45 Electromagnets 46 Electric motors 47 Electric meters 48 Electrons Year 2 Semester 2 Atomic Physics 49 Radioactivity 50 Atomic structures Revision from chapter 1 |
Section 1 General Physics
Measurements and Motions
Chapter 1 Measurements
- Units and basic quantities
- Powers of ten shorthand
- Length
- Significant figures
- Area
- Volume
- Mass
- Time
- Systematic errors
- Vernier scales and micrometers
- Practical work: Period of a simple Pendulum
Units and basic quantities
The value of a physical quantity is usually expressed as the product of a number and a unit. The unit represents a specific example or prototype of the quantity concerned, which is used as a point of reference. The number represents the ratio of the value of the quantity to the unit. In the case of the kilogram, the prototype is a platinum-iridium cylinder held under tightly controlled conditions in a vault at the BIPM, although there are a number of identical copies kept under identical conditions located throughout the world.
There are seven base quantities used in the International System of Units. The seven base quantities and their corresponding units are:
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Powers of ten shorthand
Most of the prefixes in the table above are multiples of a thousand. These are referred to as regular prefixes and may be used with any SI unit.
This is a neat way writing numbers, especially if they are large or small.
Example:
4000 = 4 x 10 x 10 x 10 = 4 x 10^3
400 = 4 x 10 x 10 = 4 x 10^2
40 = 4 x 10 = 4 x 10^1
4 = 4 x 1 = 4 x 10^0
0.4 = 4/10 =4/10^1 = 4 x 10^-1
0.04 = 4/100 = 4/10^2 = 4 x 10^-2
0.004 = 4/1000 = 4/10^3 = 4 x 10^-3
The small figures 1, 2, 3, etc., are called powers of ten. This way of writing is called standard notation.
This is a neat way writing numbers, especially if they are large or small.
Example:
4000 = 4 x 10 x 10 x 10 = 4 x 10^3
400 = 4 x 10 x 10 = 4 x 10^2
40 = 4 x 10 = 4 x 10^1
4 = 4 x 1 = 4 x 10^0
0.4 = 4/10 =4/10^1 = 4 x 10^-1
0.04 = 4/100 = 4/10^2 = 4 x 10^-2
0.004 = 4/1000 = 4/10^3 = 4 x 10^-3
The small figures 1, 2, 3, etc., are called powers of ten. This way of writing is called standard notation.
Length:
Length is a measure of distance. In the International System of Quantities, length is any quantity with dimension distance. In most systems of measurement, the unit of length is a base unit, from which other units are derived.
Length is commonly understood to mean the most extended dimension of an object. Length may be distinguished from height, which is vertical extent, and width or breadth, which are the distance from side to side, measuring across the object at right angles to the length. Length is a measure of one dimension, whereas area is a measure of two dimensions (length squared) and volume is a measure of three dimensions (length cubed). |
Note: Parallax causes an object to appear shorter or longer depending on how you view it. An object must be viewed at right angles to the scale to measure its length correctly. |
Significant figures
There are three rules on determining how many significant figures are in a number:
- Non-zero digits are always significant.
- Any zeros between two significant digits are significant.
- A final zero or trailing zeros in the decimal portion ONLY are significant.
Area
Area of a square or rectangle:
- The area of a square or rectangle is given by
- area = length x breadth
- The SI unit of area is the square meter(m^2)
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- Area of a triangle = 1/2 x base x height
Volume
Volume is the amount of space occupied. The unit of volume is cubic meter.
Volume = length x breadth x height
Volume = length x breadth x height
Mass
The mass of an object is a fundamental property of the object; a numerical measure of its inertia; a fundamental measure of the amount of matter in the object. Definitions of mass often seem circular because it is such a fundamental quantity that it is hard to define in terms of something else. All mechanical quantities can be defined in terms of mass, length, and time. The usual symbol for mass is m and its SI unit is the kilogram. While the mass is normally considered to be an unchanging property of an object, at speeds approaching the speed of light one must consider the increase in the relativistic mass.
The weight of an object is the force of gravity on the object and may be defined as the mass times the acceleration of gravity, w = mg. Since the weight is a force, its SI unit is the newton. Density is mass/volume.
The weight of an object is the force of gravity on the object and may be defined as the mass times the acceleration of gravity, w = mg. Since the weight is a force, its SI unit is the newton. Density is mass/volume.
Time
The unit of Time is the second(s)
Time is passing non-stop, and we follow it with clocks and calendars. Yet we cannot study it with a microscope or experiment with it. And it still keeps passing. We just cannot say what exactly happens when time passes.
Time is represented through change, such as the circular motion of the moon around Earth. The passing of time is indeed closely connected to the concept of space.
Time is passing non-stop, and we follow it with clocks and calendars. Yet we cannot study it with a microscope or experiment with it. And it still keeps passing. We just cannot say what exactly happens when time passes.
Time is represented through change, such as the circular motion of the moon around Earth. The passing of time is indeed closely connected to the concept of space.
Practical work
Period of a simple pendulum:
SIMPLE PENDULUM EXPERIMENT
of oscillation. Variable : a) Manipulated variable : Length, l b) Responding variable : Period, T. c) Fixed variable : Mass of pendulum bob. Materials/ Apparatus : Retort stand, pendulum bob, thread, metre rule, stop watch |
7. Procedure :
a) Set up the apparatus as shown in Figure above.// A small brass or bob was attached to the thread. The thread was held by a clamp of a the retort stand. b) The length of the thread , l was measured by a metre rule, starting with 90.0 cm. The bob of the pendulum was displaced and released. c) The time for 20 complete oscillations, t was taken using the stop watch. Calculate the period of oscillation by using, T = t / 20 d) The experiment was repeated using different lengths such as 80.0 cm. 70.0 cm, 60.0 cm, 50.0 cm and 40.0 cm. |
Conclusion
- The length of simple pendulum is directly proportional to the square of the period of oscillation.
- T2 is directly proportional to l (the straight line graph passing through the origin)
Vernier Scales and Micrometers
Instructions on use
- The Vernier caliper is an extremely precise measuring instrument; the reading error is 1/20 mm = 0.05 mm.
- Close the jaws lightly on the object to be measured.
- If you are measuring something with a round cross section, make sure that the axis of the object is perpendicular to the caliper. This is necessary to ensure that you are measuring the full diameter and not merely a chord.
- Ignore the top scale, which is calibrated in inches.
- Use the bottom scale, which is in metric units.
- Notice that there is a fixed scale and a sliding scale.
- The boldface numbers on the fixed scale are centimeters.
- The tick marks on the fixed scale between the boldface numbers are millimeters.
- There are ten tick marks on the sliding scale. The left-most tick mark on the sliding scale will let you read from the fixed scale the number of whole millimeters that the jaws are opened.
- In the example above, the leftmost tick mark on the sliding scale is between 21 mm and 22 mm, so the number of whole millimeters is 21.
- Next we find the tenths of millimeters. Notice that the ten tick marks on the sliding scale are the same width as nine ticks marks on the fixed scale. This means that at most one of the tick marks on the sliding scale will align with a tick mark on the fixed scale; the others will miss.
- The number of the aligned tick mark on the sliding scale tells you the number of tenths of millimeters. In the example above, the 3rd tick mark on the sliding scale is in coincidence with the one above it, so the caliper reading is (21.30 ± 0.05) mm.
- If two adjacent tick marks on the sliding scale look equally aligned with their counterparts on the fixed scale, then the reading is half way between the two marks. In the example above, if the 3rd and 4th tick marks on the sliding scale looked to be equally aligned, then the reading would be (21.35 ± 0.05) mm.
- On those rare occasions when the reading just happens to be a "nice" number like 2 cm, don't forget to include the zero decimal places showing the precision of the measurement and the reading error. So not 2 cm, but rather (2.000 ± 0.005) cm or (20.00 ± 0.05) mm.
b) Micrometer screw gauge
A quick guide on how to read a micrometer screw gauge. Similar to the way a vernier caliper is read, a micrometer reading contains two parts:
A quick guide on how to read a micrometer screw gauge. Similar to the way a vernier caliper is read, a micrometer reading contains two parts:
- the first part is contributed by the main scale on the sleeve
- the second part is contributed by the rotating vernier scale on the thimble
The above image shows a typical micrometer screw gauge and how to read it. Steps:
To ensure that you understand the steps above, here’s one more example:
- To obtain the first part of the measurement: Look at the image above, you will see a number 5 to the immediate left of the thimble. This means 5.0 mm. Notice that there is an extra line below the datum line, this represents an additional 0.5 mm. So the first part of the measurement is 5.0+0.5=5.55.0+0.5=5.5 mm.
- To obtain the second part of the measurement: Look at the image above, the number 28 on the rotating vernier scale coincides with the datum line on the sleeve. Hence, 0.28 mm is the second part of the measurement.
To ensure that you understand the steps above, here’s one more example:
First part of the measurement: 2.5 mm
Second part of the measurement: 0.38 mm
Final measurement: 2.88 mm
Now, we shall try with zero error. If you are not familiar on how to handle zero error for micrometer screw gauge, I suggest that you read up on Measurement of Length.
The reading on the bottom is the measurement obtained and the reading at the top is the zero error. Find the actual measurement. (Meaning: get rid of the zero error in the measurement or take into account the zero error)
Measurement with zero error: 1.76 mm
Zero error: + 0.01 mm (positive because the zero marking on the thimble is below the datum line)
Measurement without zero error: 1.76–(+0.01)=1.751.76–(+0.01)=1.75 mm
Second part of the measurement: 0.38 mm
Final measurement: 2.88 mm
Now, we shall try with zero error. If you are not familiar on how to handle zero error for micrometer screw gauge, I suggest that you read up on Measurement of Length.
The reading on the bottom is the measurement obtained and the reading at the top is the zero error. Find the actual measurement. (Meaning: get rid of the zero error in the measurement or take into account the zero error)
Measurement with zero error: 1.76 mm
Zero error: + 0.01 mm (positive because the zero marking on the thimble is below the datum line)
Measurement without zero error: 1.76–(+0.01)=1.751.76–(+0.01)=1.75 mm
Checklist:
After studying this chapter you should be able to
After studying this chapter you should be able to
- recall three basic quantities in physics,
- write a number in powers of ten (standard notation),
- recall the unit of length and the meaning of the prefixes kilo, centi, milli, micro, nano,
- use a ruler to measure length so as to minimize errors,
- give a result to an appropriate number of significant figures,
- measure areas of squares, rectangles, triangles and circles,
- measure the volume of regular solids and of liquids,
- recall the unit of mass and how mass is measured,
- recall the unit of time and how time is measured,
- describe the use of clocks and devices, both analogue and digital, for measuring an interval of time,
- describe an experiment to find the period of a pendulum,
- understand how a systematic error may be introduced when measuring,
- take measurements with vernier calipers and a micrometer screw gauge.
You can download the Presentation on Measurements!
physics_1_-_length_and_time.pptx | |
File Size: | 1380 kb |
File Type: | pptx |
Chapter 2 Speed, Velocity and Acceleration
- Speed
- Velocity
- Acceleration
- Timers
- Practical work: Analyzing motion
Speed
- If a car travels 300 km from Liverpool to London in five hours, its average speed is 300 km/5 h = 60 km/h.
- The speedometer would certainly not read 60 km/h for the whole journey but might vary considerably from this value.
- That is why we state the average speed.
- If a car could travel at a constant speed of 60 km/h for five hours, the distance covered would still be 300 km.
It is always true that,
average speed = distance moved/time taken
- To find the actual speed at any instant we would need to know the distance moved in a very short interval of time.
Velocity
Speed is the distance traveled in unit time; velocity is the distance traveled in unit time in a stated direction. If two trains travel due north at 20 m/s, they have the same speed of 20 m/s and the same velocity of 20 m/s due north. If one travels north and the other south, their speeds are the same but not their velocities since their directions of motion are different. Speed is a scalar quantity and velocity a vector quantity.
velocity = distance moved in a stated direction/time taken
Distance moved in a stated direction is called the displacement. It is a vector, unlike distance which is a scalar. Velocity may also be defined as
velocity = displacement/time taken
velocity = distance moved in a stated direction/time taken
Distance moved in a stated direction is called the displacement. It is a vector, unlike distance which is a scalar. Velocity may also be defined as
velocity = displacement/time taken
Acceleration
When the velocity of a body changes we say the body accelerates. If a car starts from rest and moving due north has velocity 2 m/s after 1 second, its velocity has increased by 2 m/s in 1 s and its acceleration is 2 m/s per second due north. We write this as 2 m/s^2.
Acceleration is the change of velocity in unit time, or
acceleration = change of velocity/time taken for change
Acceleration is also a vector and both its magnitude and direction should be stated.
Acceleration is the change of velocity in unit time, or
acceleration = change of velocity/time taken for change
Acceleration is also a vector and both its magnitude and direction should be stated.
Deceleration
An acceleration is positive if the velocity increases and negative if it decreases. A negative acceleration is also called a deceleration or retardation.
Timers
a) Motion sensors
b) Tickertape timer: tape charts
- Motion sensors use the ultrasonic echo technique to determine the distance of an object from the sensor.
- Connection of a data logger and computer to the motion sensor then enables a distance–time graph to be plotted directly.
- Further data analysis by the computer allows a velocity–time graph to be obtained.
b) Tickertape timer: tape charts
- A tickertape timer also enables us to measure speeds and hence accelerations.
c) Photogate timer
- Photogate timers may be used to record the time taken for a trolley to pass through the gate.
- If the length of the ‘interrupt card’ on the trolley is measured, the velocity of the trolley can then be calculated.
- Photogates are most useful in experiments where the velocity at only one or two positions is needed.
Practical work: Analyzing motion
a) Your own motion
- Pull a 2 m length of tape through a tickertape timer as you walk away from it quickly, then slowly, then speeding up again and finally stopping.
- Cut the tape into tentick lengths and make a tape chart. Write labels on it to show where you speeded up, slowed down, etc.
b) Trolley on a sloping runway
- Attach a length of tape to a trolley and release it at the top of a runway.
- The dots will be very crowded at the start – ignore those; but beyond them cut the tape into tentick lengths.
- Make a tape chart. Is the acceleration uniform? What is its average value?
c) Datalogging
- Replace the tickertape timer with a motion sensor connected to a datalogger and computer.
- Repeat the experiments in a) and b) and obtain distance–time and velocity–time graphs for each case; identify regions where you think the acceleration changes or remains uniform.
Checklist
After studying this chapter you should be able to
After studying this chapter you should be able to
- explain the meaning of the terms speed and acceleration,
- describe how speed and acceleration may be found using
- tape charts and motion sensors.
- distinguish between speed and velocity,
Chapter 3 Graphs of equations
- Velocity-time graphs
- Distance-time graphs
- Equations for uniform acceleration
Velocity-time graphs
physics_2_-_speed_velocity_and_acceleration.pptx | |
File Size: | 1181 kb |
File Type: | pptx |
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Chapter 4
Falling Bodies
Falling objects eventually reach terminal velocity – where their resultant force is zero. Stopping distances depend on speed, mass, road surface and reaction time.
Terminal Velocity
Falling objects
There are two main forces which affect a falling object at different stages of its fall:
Three stages of falling
When an object is dropped, there are three stages before it hits the ground:
The effect of air resistanceWhat happens if you drop a feather and a coin together? The feather and the coin have roughly the same surface area, so when they begin to fall they have about the same air resistance.
As the feather falls, its air resistance increases until it soon balances the weight of the feather. The feather now falls at its terminal velocity. However, the coin is much heavier, so it has to travel quite fast before air resistance is large enough to balance its weight. In fact, it probably hits the ground before it reaches its terminal velocity.
An astronaut on the Moon carried out a famous experiment. He dropped a hammer and a feather at the same time and found that they landed together. The Moon's gravity is too weak for it to attract an atmosphere. This means no air can surround it so there is no air resistance. When the hammer and feather were dropped, they fell together with the same acceleration.
Experiments on The factors affecting the terminal velocity of an object include:
It is possible to change either the mass or surface area of the objects, but for a valid experiment only one of these variables can be changed at a time. The effect of falling can be measured by attaching a mass to a parachute. This slows the descent and makes timing easier.
https://www.bbc.co.uk/bitesize/guides/z8vc6fr/revision/1
https://www.bbc.co.uk/bitesize/guides/z8vc6fr/revision/2
Falling objects
There are two main forces which affect a falling object at different stages of its fall:
- The weight of the object - this is a force acting downwards, caused by the Earth's gravitational field acting on the object’s mass.
- Air resistance - this is a frictional force acting in the opposite direction to the movement of the object. (Note that in space and other vacuums there is no air resistance.)
Three stages of falling
When an object is dropped, there are three stages before it hits the ground:
- At the start, the object accelerates downwards because of its weight. There is very little air resistance. There is a resultant force acting downwards. The acceleration is constant when the object is close to Earth.
- As it gains speed, the object's weight stays the same but the air resistance on it increases. There is a resultant force acting downwards.
- Eventually, the object's weight is balanced by the air resistance. There is no resultant force and the object reaches a steady speed – this is known as the terminal velocity.
The effect of air resistanceWhat happens if you drop a feather and a coin together? The feather and the coin have roughly the same surface area, so when they begin to fall they have about the same air resistance.
As the feather falls, its air resistance increases until it soon balances the weight of the feather. The feather now falls at its terminal velocity. However, the coin is much heavier, so it has to travel quite fast before air resistance is large enough to balance its weight. In fact, it probably hits the ground before it reaches its terminal velocity.
An astronaut on the Moon carried out a famous experiment. He dropped a hammer and a feather at the same time and found that they landed together. The Moon's gravity is too weak for it to attract an atmosphere. This means no air can surround it so there is no air resistance. When the hammer and feather were dropped, they fell together with the same acceleration.
Experiments on The factors affecting the terminal velocity of an object include:
- its mass
- its surface area
- the acceleration due to gravity, g
It is possible to change either the mass or surface area of the objects, but for a valid experiment only one of these variables can be changed at a time. The effect of falling can be measured by attaching a mass to a parachute. This slows the descent and makes timing easier.
https://www.bbc.co.uk/bitesize/guides/z8vc6fr/revision/1
https://www.bbc.co.uk/bitesize/guides/z8vc6fr/revision/2
The video below shows how a practical method to determine the value of g (9.8 m/s2) using the falling body method.
To help enrich your understanding of free falling bodies, refer to the video below on how to solve some problems.
Subject Content for Motion
1.2 Motion
Core
• Define speed and calculate average speed from total distance total time
• Plot and interpret a speed–time graph or a distance–time graph
• Recognise from the shape of a speed–time graph when a body is – at rest – moving with constant speed – moving with changing speed
• Calculate the area under a speed–time graph to work out the distance travelled for motion with constant acceleration
• Demonstrate understanding that acceleration and deceleration are related to changing speed including qualitative analysis of the gradient of a speed–time graph
• State that the acceleration of free fall for a body near to the Earth is constant
Supplement
• Distinguish between speed and velocity
• Define and calculate acceleration using change of velocity time taken
• Calculate speed from the gradient of a distance–time graph
• Calculate acceleration from the gradient of a speed–time graph
• Recognise linear motion for which the acceleration is constant
• Recognise motion for which the acceleration is not constant
• Understand deceleration as a negative acceleration
• Describe qualitatively the motion of bodies falling in a uniform gravitational field with and without air resistance (including reference to terminal velocity)
Chapter 5
Density
Density is the mass per unit volume of any object. It is calculated by dividing the mass of an object by its volume. The volume of objects can be worked out by multiplying height by length by width.
Density
Density is the mass per unit volume of any object. It is calculated by dividing the mass of an object by its volume. The volume of objects can be worked out by multiplying height by length by width.
Density is the mass per unit volume. It can be measured in several ways. The most accurate way to calculate the density of any solid, liquid or gas is to divide its mass in kilograms by its volume (length × width × height) in cubic metres.
Density can be found using the equation:
The unit for density is kg/m3. The density of water is approximately 1000 kg/m3 and the density of air is approximately 1.2 kg/m3. If solid objects are placed in water and they sink, they have a density greater than water (1000 kg/m3). The reverse is also true. If several liquids that don’t mix (immiscible) are placed in the same container, the least dense one will rise to the top and the densest one will sink to the bottom. This is also true of gases, but they are often harder to see because gases tend to mix with each other very easily.
Density can be found using the equation:
The unit for density is kg/m3. The density of water is approximately 1000 kg/m3 and the density of air is approximately 1.2 kg/m3. If solid objects are placed in water and they sink, they have a density greater than water (1000 kg/m3). The reverse is also true. If several liquids that don’t mix (immiscible) are placed in the same container, the least dense one will rise to the top and the densest one will sink to the bottom. This is also true of gases, but they are often harder to see because gases tend to mix with each other very easily.
Not all objects have regular volumes that are easy to measure. A ‘eureka can’ can be used in these cases.
A eureka can is a container large enough to hold the object with a spout positioned near the top. The can is filled to the top with water and the object placed in it. The volume of the object is equal to the volume of the water that is forced through the spout.
Eureka cans are named after a scientist called Archimedes who first recorded this idea. They are sometimes also called displacement vessels. The video below tells you how to determine the volume of regular shaped and irregular shaped objects.
Eureka cans are named after a scientist called Archimedes who first recorded this idea. They are sometimes also called displacement vessels. The video below tells you how to determine the volume of regular shaped and irregular shaped objects.
The video below will help you understand how to use the density equation in order to solve for density and other unknowns.
Chapter 6
Weight and Mass
Mass (measured in kilograms, kg) is related to the amount of matter in an object. Weight (measured in newtons, N) is the force of gravity on a mass. The size of this force depends on the gravitational field strength (often called gravity, g, for short).
weight = mass x gravitational field strength
W = m x g
You can rearrange this equation with the help of the formula triangle:
weight = mass x gravitational field strength
W = m x g
You can rearrange this equation with the help of the formula triangle:
Using the triangle will help you determine the different equations for the given unknowns. The formulas of the rest of the unknowns are given below.
W = weight m = mass g = gravitational field strength
W = mg = m x g
m = W ÷ g
g = W ÷ m
G is a constant that depends on the gravitational pull of a planet. For Earth, the constant is 9.8 N/kg. the value of 10 N/kg is also acceptable. The video below will help you understand how to solve problems and to use the weight equation to determine missing unknowns.
Chapter 7
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Answer the past paper question on Mass and Weight given to the left of this. Follow all instructions given. All answers to the questions will be discussed during class.
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Forces are responsible for interactions between objects. They both have magnitude and direction. At times, forces can enhance each other. at other times they can diminish each other depending if the forces are going the same way or not.
When several forces act on a body, the resultant (overall) force on the body can be found by adding together forces which act in the same direction, and subtracting forces which act in opposite directions:
When several forces act on a body, the resultant (overall) force on the body can be found by adding together forces which act in the same direction, and subtracting forces which act in opposite directions:
The resultant force and direction favors the force of stronger magnitude. As you can see from the images given above. To help enrich your understanding, refer to the video below.
You have to understand that Friction always opposes motion. Look at the picture below.
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The direction of Friction is given by the direction of the arrowhead. As the sled moves diagonally downwards, Friction opposes it diagonally upwards. Test yourselves by answering the worksheet. All answers will be discussed in the following lesson.
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Chapter 8
Laws of Motion and Acceleration
Newton's First law
According to Newton's first law of motion, an object remains in the same state of motion unless a resultant force acts on it. If the resultant force on an object is zero, this means:
Examples of objects with uniform motion
Newton's first law can be used to explain the movement of objects travelling with uniform motion (constant velocity). For example, when a car travels at a constant velocity, the driving force from the engine is balanced by the resistive forces such as air resistance and frictional forces in the car's moving parts. The resultant force on the car is zero.
Other examples include:
According to Newton's first law of motion, an object remains in the same state of motion unless a resultant force acts on it. If the resultant force on an object is zero, this means:
- a stationary object stays stationary
- a moving object continues to move at the same velocity (at the same speed and in the same direction)
Examples of objects with uniform motion
Newton's first law can be used to explain the movement of objects travelling with uniform motion (constant velocity). For example, when a car travels at a constant velocity, the driving force from the engine is balanced by the resistive forces such as air resistance and frictional forces in the car's moving parts. The resultant force on the car is zero.
Other examples include:
- a runner at their top speed experiences the same air resistance as their thrust.
- an object falling at terminal velocity experiences the same air resistance as its weight.
If the forces are balanced, there will be no acceleration on the box.
Examples of objects with non-uniform motion
Newton's first law can also be used to explain the movement of objects travelling with non-uniform motion. This includes situations when the speed changes, the direction changes, or both change. For example, when a car accelerates, the driving force from the engine is greater than the resistive forces. The resultant force is not zero.
Other examples include:
Newton's first law can also be used to explain the movement of objects travelling with non-uniform motion. This includes situations when the speed changes, the direction changes, or both change. For example, when a car accelerates, the driving force from the engine is greater than the resistive forces. The resultant force is not zero.
Other examples include:
- at the start of their run, a runner experiences less air resistance than their thrust, so they accelerate
- an object that begins to fall experiences less air resistance than its weight, so it accelerates
If the forces are not balanced, then the resultant force on the box is NOT zero. hence, there will be an acceleration.
Newton's Second law
Newton's second law of motion can be described by this equation:
resultant force = mass × acceleration
This is when:
The equation shows that the acceleration of an object is:
In other words, the acceleration of an object increases if the resultant force on it increases, and decreases if the mass of the object increases.
Inertial mass - HigherThe ratio of force over acceleration is called inertial mass. Inertial mass is a measure of how difficult it is to change the velocity of an object.
Example:
Calculate the force needed to accelerate a 22 kg cheetah at 15 m/s2.
Newton's second law of motion can be described by this equation:
resultant force = mass × acceleration
This is when:
- force (F) is measured in newtons (N)
- mass (m) is measured in kilograms (kg)
- acceleration (α) is measured in metres per second squared (m/s2)
The equation shows that the acceleration of an object is:
- proportional to the resultant force on the object
- inversely proportional to the mass of the object
In other words, the acceleration of an object increases if the resultant force on it increases, and decreases if the mass of the object increases.
Inertial mass - HigherThe ratio of force over acceleration is called inertial mass. Inertial mass is a measure of how difficult it is to change the velocity of an object.
Example:
Calculate the force needed to accelerate a 22 kg cheetah at 15 m/s2.
Click on the link below to answer some exercises on the Second Law of Motion.
https://www.nagwa.com/en/worksheets/235147593478/
The answers will be shown as you answer each question.
https://www.nagwa.com/en/worksheets/235147593478/
The answers will be shown as you answer each question.
Required Practical
Investigate the relationship between the force, mass and acceleration by varying the masses added to trolleys.
More than one method could be used to investigate the relationship between the force, mass and acceleration. This method will vary the masses added to trolleys.
Aim of the experiment
To investigate the relationship between the force, mass and acceleration by varying the masses added to trolleys.
Method
The diagram shows apparatus that can used in this investigation. A constant stream of air reduces the friction between the glider and the air track.
Investigate the relationship between the force, mass and acceleration by varying the masses added to trolleys.
More than one method could be used to investigate the relationship between the force, mass and acceleration. This method will vary the masses added to trolleys.
Aim of the experiment
To investigate the relationship between the force, mass and acceleration by varying the masses added to trolleys.
Method
The diagram shows apparatus that can used in this investigation. A constant stream of air reduces the friction between the glider and the air track.
- Cut an interrupt card to a known length (such as 10 cm) and attach it to an air track glider.
- Set up the equipment as shown in the diagram. Make sure that the air track is level, and that the card will pass through both gates before the masses strike the floor.
- Set the data logging software to calculate acceleration.
- Use scales to measure the total mass of the glider, string and weight stack. Record this value.
- Attach the full weight stack (6 x 10g masses) to the end of the string.
- Make sure the glider is in position and switch on the air blower. The glider should accelerate.
- Remove one weight and attach it to the glider using blu-tack. This will keep the total mass constant. (The weight stack is being accelerated too.)
- Repeat steps 6-7 removing one weight from the stack each time. Remember to attach each weight to the glider as it is removed from the weight stack.
- Plot a scatter graph with force on the vertical axis, and acceleration on the horizontal axis. Draw a suitable line of best fit.
- Describe what the results show about the effect of increasing the force which is accelerating the object.
- Extension: calculate the gradient of your graph and compare this to the to total mass of the glider and weight stack measured in step 4 above.
Evaluation
Acceleration is directly proportional to the force applied to the object. This means that a graph of force against acceleration should produce a straight line that passes through the origin.
Newton's Third law
According to Newton's third law of motion, whenever two objects interact, they exert equal and opposite forces on each other. This is often worded as 'every action has an equal and opposite reaction'. However, it is important to remember that the two forces:
Examples of force pairs
Newton's third law can be applied to examples of equilibrium situations.
A cat sits on the ground. There are contact gravitational forces between Earth and the cat:
These forces are equal in size and opposite in direction. Pushing a pram. There are contact forces between the person and the pram:
These forces are equal in size and opposite in direction. Car tyre on a roadThere are contact forces between the tyre and the road:
These forces are equal in size and opposite in direction. A satellite in Earth orbitThere are non-contact gravitational forces between Earth and the satellite:
These forces are equal in size and opposite in direction.
According to Newton's third law of motion, whenever two objects interact, they exert equal and opposite forces on each other. This is often worded as 'every action has an equal and opposite reaction'. However, it is important to remember that the two forces:
- act on two different objects
- are of the same type (eg both contact forces)
Examples of force pairs
Newton's third law can be applied to examples of equilibrium situations.
A cat sits on the ground. There are contact gravitational forces between Earth and the cat:
- the cat pulls the Earth up
- the Earth pulls the cat down
These forces are equal in size and opposite in direction. Pushing a pram. There are contact forces between the person and the pram:
- the person pushes the pram forwards
- the pram pushes the person backwards
These forces are equal in size and opposite in direction. Car tyre on a roadThere are contact forces between the tyre and the road:
- the tyre pushes the road backwards
- the road pushes the tyre forwards
These forces are equal in size and opposite in direction. A satellite in Earth orbitThere are non-contact gravitational forces between Earth and the satellite:
- the Earth pulls the satellite
- the satellite pulls Earth
These forces are equal in size and opposite in direction.
Chapter 9
Circular Motion
When an object moves in a circle at a constant speed, its direction constantly changes. A change in direction causes a change in velocity. This is because velocity is a vector quantity – it has an associated direction as well as a magnitude. A change in velocity results in acceleration, so an object moving in a circle is accelerating even though its speed may be constant.
An object will only accelerate if a resultant force acts on it. For an object moving in a circle, this resultant force is the centripetal force that acts towards the middle of the circle. Gravitational attraction provides the centripetal force needed to keep planets and all types of satellite in orbit.
An object will only accelerate if a resultant force acts on it. For an object moving in a circle, this resultant force is the centripetal force that acts towards the middle of the circle. Gravitational attraction provides the centripetal force needed to keep planets and all types of satellite in orbit.
Artificial satellites travel in one of two different orbits:
Geostationary satellites take 24 hours to orbit the Earth, so the satellite appears to remain in the same part of the sky when viewed from the ground. These orbits are much higher than polar orbits (typically 36,000 km) so the satellites travel more slowly (around 2,000 km/s).
- polar orbits
- geostationary orbits
Geostationary satellites take 24 hours to orbit the Earth, so the satellite appears to remain in the same part of the sky when viewed from the ground. These orbits are much higher than polar orbits (typically 36,000 km) so the satellites travel more slowly (around 2,000 km/s).
Centripetal force
A centripetal force is a net force that acts on an object to keep it moving along a circular path. An object experiencing centripetal motion experiences a constant change in acceleration.
It is important to understand that the centripetal force is not a fundamental force, but just a label given to the net force which causes an object to move in a circular path. The first 10 minutes of the video below will help you understand what it is.
A centripetal force is a net force that acts on an object to keep it moving along a circular path. An object experiencing centripetal motion experiences a constant change in acceleration.
It is important to understand that the centripetal force is not a fundamental force, but just a label given to the net force which causes an object to move in a circular path. The first 10 minutes of the video below will help you understand what it is.
Practical
One apparatus that clearly illustrates the centripetal force consists of a tethered mass (m1) swung in a horizontal circle by a lightweight string which passes through a vertical tube to a counterweight mass (m2) as shown in the figure below.
There are numerous factors affecting Circular motion.
A practical can be done by adjusting the factors given above given that some factors are kept constant.
One apparatus that clearly illustrates the centripetal force consists of a tethered mass (m1) swung in a horizontal circle by a lightweight string which passes through a vertical tube to a counterweight mass (m2) as shown in the figure below.
There are numerous factors affecting Circular motion.
- The length of the string or the radius.
- The area of the circle.
- The mass of the object.
A practical can be done by adjusting the factors given above given that some factors are kept constant.
The video below will give an example in using the formula for determining the Centripetal Force. In the example below, the tension is equal to the Centripetal Force.
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The string is what keeps the ball moving in a circle. The centripetal force is being supported by the tension on the string. The tension would be the relative upward force done by the string on the ball. This keeps the ball moving in a circle.
The formula to determine the Centripetal force is given below where: Fc= Centripetal Force m= Mass v= Velocity r= radius |
Chapter 10
Moments and Levers
Moments
A force or system of forces may cause an object to turn. A moment is the turning effect of a force. Moments act about a point in a clockwise or anticlockwise direction. The point chosen could be any point on the object, but the pivot ,also known as the fulcrum, is usually chosen.
A force or system of forces may cause an object to turn. A moment is the turning effect of a force. Moments act about a point in a clockwise or anticlockwise direction. The point chosen could be any point on the object, but the pivot ,also known as the fulcrum, is usually chosen.
The magnitude of a moment can be calculated by using the formula below:
M= fd
Where:
M= Moments
f= Force perpendicular to the lever arm
d= Distance of force from the pivot.
M= fd
Where:
M= Moments
f= Force perpendicular to the lever arm
d= Distance of force from the pivot.
Moments and Balanced Objects
If an object is balanced, the total clockwise moment about a pivot is equal to the total anticlockwise moment about that pivot.
For a balanced object, you can calculate:
Example
A parent and child are at opposite ends of a playground see-saw. The parent weighs 750 N and the child weighs 250 N. The child sits 2.4 m from the pivot. Calculate the distance the parent must sit from the pivot for the see-saw to be balanced.
Child's moment = Force × Distance
250 N × 2.4 M = 600 Nm
Parent's moment = child's moment, so rearrange the formula M=fd, to find the distance of the parent from the pivot.
If an object is balanced, the total clockwise moment about a pivot is equal to the total anticlockwise moment about that pivot.
For a balanced object, you can calculate:
- the size of a force, or
- the perpendicular distance of a force from the pivot
Example
A parent and child are at opposite ends of a playground see-saw. The parent weighs 750 N and the child weighs 250 N. The child sits 2.4 m from the pivot. Calculate the distance the parent must sit from the pivot for the see-saw to be balanced.
Child's moment = Force × Distance
250 N × 2.4 M = 600 Nm
Parent's moment = child's moment, so rearrange the formula M=fd, to find the distance of the parent from the pivot.
A video is given below in order to help you understand more on how to solve problems of Moments.
Levers
A lever consists of:
A lever consists of:
- a pivot
- an effort
- a load
Simple levers and Rotation
A simple lever could be a solid beam laid across a pivot. As effort is applied to rotate one end about the pivot. The opposite end is also rotated about the pivot in the same direction. This has the effect of rotating or lifting the load.
Levers, such as this one, make use of moments to act as a force multiplier. They allow a larger force to act upon the load than is supplied by the effort, so it is easier to move large or heavy objects.
A simple lever could be a solid beam laid across a pivot. As effort is applied to rotate one end about the pivot. The opposite end is also rotated about the pivot in the same direction. This has the effect of rotating or lifting the load.
Levers, such as this one, make use of moments to act as a force multiplier. They allow a larger force to act upon the load than is supplied by the effort, so it is easier to move large or heavy objects.
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Solve the problems on Moments in the attached file. Write all your answers in a word document and send it to this e-mail: [email protected]
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Chapter 11
Centre of Mass
The center of mass is the point where we can assume all the mass of the object is concentrated.As the gravity only acts at a single point in the object. So a single arrow on diagram can represent the weight of the object.The centre of mass for regularly shaped objects is in the center.For irregular shaped objects,we can find the center of mass by following steps.
It is important to know where the centre of mass of a body is, as its position determines the stability of the body.
Stability
Stability is a measure of how likely it is for an object to topple over when pushed or moved. Stable objects are very difficult to topple over, while unstable objects topple over very easily. Objects with a wide base, and a low centre of gravity, are more stable than those with a narrow base and a high centre of gravity.
- Hang up the object.
- Suspend a plumb line from the same place.
- Mark the position of the thread.
- The centre of mass is along the line of thread.
- Repeat the above steps with object suspended from different places.
- The centre of mass is where these lines cross.
It is important to know where the centre of mass of a body is, as its position determines the stability of the body.
Stability
Stability is a measure of how likely it is for an object to topple over when pushed or moved. Stable objects are very difficult to topple over, while unstable objects topple over very easily. Objects with a wide base, and a low centre of gravity, are more stable than those with a narrow base and a high centre of gravity.
A traffic cone is stable as it has a:
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For an object to be stable it must have:
The yellow car has a wider base and a lower centre of gravity than the blue car making it more stable. The wheel acts as the pivot for the car.The weight has a turning effect or moment, which causes the car to topple over or fall back. The blue car topples over because it is unstable. The Yellow car falls back because it is more stable. |
Practical
Experiment to determine centre of gravity of plane lamina
Experiment to determine centre of gravity of plane lamina
- Apparatus
- retort stand
- cork
- plumb line
- pin
- lamina
- Procedure
- On the lamina, make three holes near the edge of the lamina.
- Suspend the lamina through one of the holes as shown in the diagram.
- Hang the plumb line on the pin.
- When the plumb line is steady, make a dot on the position of the line at the edge of the lamina
- Repeat steps 2-4 for the other two holes the point where the lines meet is the centre of mass of the body
Chapter 12
Momentum
A moving object has momentum. This is the tendency of the object to keep moving in the same direction. It is difficult to change the direction of movement of an object with a lot of momentum.
Momentum can be calculated using this equation:
p=mv
where:
p is the momentum in kilograms metres per second, kg m/s
m is the mass in kilograms, kg
v is the velocity in m/s
For example, what is the momentum of a 5 kg object moving with a velocity of 2 m/s?
momentum = 5 × 2 = 10 kg m/s
Direction
Notice that momentum does not just depend on the object’s mass and speed. Velocity is speed in a particular direction, so the momentum of an object also depends on the direction of travel. This means that the momentum of an object can change if:
Conservation of momentum
As long as no external forces are acting on the objects involved, the total momentum stays the same in explosions and collisions. We say that momentum is conserved.
Momentum calculations
Here is a worked example:
Two railway carriages collide and move off together. Carriage A has a mass of 12,000 kg and moves at 5 m/s before the collision. Carriage B has a mass of 8,000 kg and is stationary before the collision. What is the velocity of the two carriages after the collision?
Step 1 Work out the total momentum before the event (before the collision):
p = m × v
Momentum of carriage A before = 12,000 × 5 = 60,000 kg m/s
Momentum of carriage B before = 8,000 × 0 = 0 kg m/s
Total momentum before = 60,000 + 0 = 60,000 kg m/s
Step 2 Work out the total momentum after the event (after the collision):
Because momentum is conserved, total momentum afterwards = 60,000 kg m/s
Step 3 Work out the total mass after the event (after the collision):
Total mass = mass of carriage A + mass of carriage B = 12,000 + 8,000 = 20,000 kg
Step 4 Work out the new velocity:
p = m × v, but we can rearrange this equation so that v = p ÷ m
Velocity (after the collision) = 60,000 ÷ 20,000 = 3 m/s
Momentum can be calculated using this equation:
p=mv
where:
p is the momentum in kilograms metres per second, kg m/s
m is the mass in kilograms, kg
v is the velocity in m/s
For example, what is the momentum of a 5 kg object moving with a velocity of 2 m/s?
momentum = 5 × 2 = 10 kg m/s
Direction
Notice that momentum does not just depend on the object’s mass and speed. Velocity is speed in a particular direction, so the momentum of an object also depends on the direction of travel. This means that the momentum of an object can change if:
- the object speeds up or slows down
- the object changes direction
Conservation of momentum
As long as no external forces are acting on the objects involved, the total momentum stays the same in explosions and collisions. We say that momentum is conserved.
Momentum calculations
Here is a worked example:
Two railway carriages collide and move off together. Carriage A has a mass of 12,000 kg and moves at 5 m/s before the collision. Carriage B has a mass of 8,000 kg and is stationary before the collision. What is the velocity of the two carriages after the collision?
Step 1 Work out the total momentum before the event (before the collision):
p = m × v
Momentum of carriage A before = 12,000 × 5 = 60,000 kg m/s
Momentum of carriage B before = 8,000 × 0 = 0 kg m/s
Total momentum before = 60,000 + 0 = 60,000 kg m/s
Step 2 Work out the total momentum after the event (after the collision):
Because momentum is conserved, total momentum afterwards = 60,000 kg m/s
Step 3 Work out the total mass after the event (after the collision):
Total mass = mass of carriage A + mass of carriage B = 12,000 + 8,000 = 20,000 kg
Step 4 Work out the new velocity:
p = m × v, but we can rearrange this equation so that v = p ÷ m
Velocity (after the collision) = 60,000 ÷ 20,000 = 3 m/s
Force and momentum
This section explains how to calculate the force involved in changing the momentum of an object.
Calculating force
Force can be calculated using this equation:
Force= change in momentum/ time
where:
force is measured in newtons, N
change in momentum is measured in kilograms metres per second, kg m/s
time is measured in seconds, s
For example, what force is needed to get a 25 kg stationary bicycle moving at 12 m/s in 5 s?
Momentum at start = 25 × 0 = 0 kg m/s
Momentum at end = 25 × 12 = 300 kg m/s
Change in momentum = 300 – 0 = 300 kg m/s
Force = change in momentum ÷ time = 300 ÷ 5 = 60 N
To change the momentum of an object you can apply a small force over a long time, or a larger force over a shorter time. Changing the direction of an oil tanker at sea is difficult because a large change in momentum is needed, but the force from the propeller is only relatively small, so it takes a long time.
The triangle may help you to rearrange the equation:
This section explains how to calculate the force involved in changing the momentum of an object.
Calculating force
Force can be calculated using this equation:
Force= change in momentum/ time
where:
force is measured in newtons, N
change in momentum is measured in kilograms metres per second, kg m/s
time is measured in seconds, s
For example, what force is needed to get a 25 kg stationary bicycle moving at 12 m/s in 5 s?
Momentum at start = 25 × 0 = 0 kg m/s
Momentum at end = 25 × 12 = 300 kg m/s
Change in momentum = 300 – 0 = 300 kg m/s
Force = change in momentum ÷ time = 300 ÷ 5 = 60 N
To change the momentum of an object you can apply a small force over a long time, or a larger force over a shorter time. Changing the direction of an oil tanker at sea is difficult because a large change in momentum is needed, but the force from the propeller is only relatively small, so it takes a long time.
The triangle may help you to rearrange the equation:
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Force can also be calculated using this equation:
Force = mass × acceleration In the example above, the acceleration of the bicycle is (12 – 0) ÷ 5 = 2.4 m/s2 Force = 25 × 2.4 = 60 N Watch the video below to help enrich your understanding of Momentum and Conservation of Momentum. Some problems are being solved as well. Listen carefully now. Subsequnetly, accomplish the past paper question at the left and send it to this e-mail: [email protected] |
Chapter 13
Energy Transfer
Energy has 7 different forms.
Transferring energy
Energy is transferred by one of the following four types of energy pathway:
Energy is transferred by one of the following four types of energy pathway:
- mechanical work – a force moving an object through a distance
- electrical work – charges moving due to a potential difference
- heating – due to temperature difference caused electrically or by chemical reaction
- radiation – energy transferred as a wave eg light, infrared, sound - the Sun emits light radiation and infrared radiation
Energy flow diagrams
Diagrams can be used to show how energy is transferred from one store to another. Two examples are the transfer diagram and the Sankey diagram.
Transfer diagrams
In transfer diagrams the boxes show the energy stores and the arrows show the energy transfers.
For example, a transfer diagram for a child at the top of a slide may be:
Diagrams can be used to show how energy is transferred from one store to another. Two examples are the transfer diagram and the Sankey diagram.
Transfer diagrams
In transfer diagrams the boxes show the energy stores and the arrows show the energy transfers.
For example, a transfer diagram for a child at the top of a slide may be:
Energy and Work
When a force causes a body to move, work is being done on the object by the force. Work is the measure of energy transfer when a force ‘F’ moves an object through a distance ‘d’. So when work is done, energy has been transferred from one energy store to another, and so:
energy transferred = work done
Energy transferred and work done are both measured in joules (J).
Calculating work done
The amount of work done when a force acts on a body depends on two things:
The equation used to calculate the work done is:
work done = force × distance
This is when:
When a force causes a body to move, work is being done on the object by the force. Work is the measure of energy transfer when a force ‘F’ moves an object through a distance ‘d’. So when work is done, energy has been transferred from one energy store to another, and so:
energy transferred = work done
Energy transferred and work done are both measured in joules (J).
Calculating work done
The amount of work done when a force acts on a body depends on two things:
- the size of the force acting on the object
- the distance through which the force causes the body to move in the direction of the force
The equation used to calculate the work done is:
work done = force × distance
This is when:
- work done (E) is measured in joules (J)
- force (F) is measured in newtons (N)
- distance (d) is in the same direction as the force and is measured in metres (m)
In this example, a force of 10 N causes the box to move a horizontal distance of 2 m, so:
W=fd
W= (10 N) (2 m)
W= 20 J
W=fd
W= (10 N) (2 m)
W= 20 J
Afterwards, try to solve Calculating Power
Here is the equation that relates power, work done and time:
p=W/t
Where:
P is power, measured in watts (W)
W is work done, measured in joules (J)
t is time, measured in seconds (s)
For example, an electric drill transfers 3000 J in 15 s. What is its power?
Power = 3000 ÷ 15 = 200 W
Cars
Car engines come in different sizes (capacities) and power ratings. For example, a small family car may have a 1.2 litre engine while a sports car may have a 3 litre engine. In general, engines with larger capacities are more powerful. More powerful engines in cars can do work quicker than less powerful ones. As a result they usually travel faster and cover the same distance in less time but also require more fuel. Increased fuel consumption costs more and has a bigger impact on the environment.
Watch the video below in order to enrich you understanding on Power calculations and how to use the power formula. Afterwards, try to solve the past paper problem given below.
Here is the equation that relates power, work done and time:
p=W/t
Where:
P is power, measured in watts (W)
W is work done, measured in joules (J)
t is time, measured in seconds (s)
For example, an electric drill transfers 3000 J in 15 s. What is its power?
Power = 3000 ÷ 15 = 200 W
Cars
Car engines come in different sizes (capacities) and power ratings. For example, a small family car may have a 1.2 litre engine while a sports car may have a 3 litre engine. In general, engines with larger capacities are more powerful. More powerful engines in cars can do work quicker than less powerful ones. As a result they usually travel faster and cover the same distance in less time but also require more fuel. Increased fuel consumption costs more and has a bigger impact on the environment.
Watch the video below in order to enrich you understanding on Power calculations and how to use the power formula. Afterwards, try to solve the past paper problem given below.
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Chapter 14
Kinetic and Potential Energy
Gravitational potential energy (GPE)
On Earth we always have the force of gravity acting on us. When we are above the Earth's surface we have potential (stored) energy. This is called gravitational potential energy (GPE).
The amount of GPE an object on Earth has depends on its:
On Earth we always have the force of gravity acting on us. When we are above the Earth's surface we have potential (stored) energy. This is called gravitational potential energy (GPE).
The amount of GPE an object on Earth has depends on its:
- mass
- height above the ground
In the diagram:
Calculating change in gravitational potential energy
If an object is lifted, work is done against gravitational force. The object gains energy. For example, Book C would gain GPE if it were lifted onto the higher book shelf alongside Books A and B.
Here is the equation for calculating gravitational potential energy:
GPE= mgh
where:
GPE is the gravitational potential energy in joules, J
m is the mass in kilograms, kg
g is the gravitational field strength in newtons per kilogram, N/kg
h is the change in height in metres, m
For example, a book with a mass of 0.25 kg is lifted 2 m onto a book shelf. If g is 10 N/kg, how much gravitational potential energy does it gain?
GPE = 0.25 × 10 × 2 = 5 J
Kinetic energy (KE)
All moving objects have kinetic energy (KE). The KE an object has depends on its:
Calculating kinetic energy
Here is the equation for calculating kinetic energy:
KE = ½ mv2 or
KE = ½ × m × v2
where:
KE is the kinetic energy in joules, J
m is the mass in kilograms, kg
v is the speed in metres per second, m/s
For example, what is the kinetic energy of a 1000 kg car travelling at 5 m/s?
KE = ½ × 1000 × 25 = 500 × 25 = 12500 J
Given below is a video to help you understand how to use the Kinetic Energy and GPE formula.
- all the books on a shelf have GPE
- book A has more than book C because it is higher
- book B has more than book A because it has a greater mass
Calculating change in gravitational potential energy
If an object is lifted, work is done against gravitational force. The object gains energy. For example, Book C would gain GPE if it were lifted onto the higher book shelf alongside Books A and B.
Here is the equation for calculating gravitational potential energy:
GPE= mgh
where:
GPE is the gravitational potential energy in joules, J
m is the mass in kilograms, kg
g is the gravitational field strength in newtons per kilogram, N/kg
h is the change in height in metres, m
For example, a book with a mass of 0.25 kg is lifted 2 m onto a book shelf. If g is 10 N/kg, how much gravitational potential energy does it gain?
GPE = 0.25 × 10 × 2 = 5 J
Kinetic energy (KE)
All moving objects have kinetic energy (KE). The KE an object has depends on its:
- mass
- speed
Calculating kinetic energy
Here is the equation for calculating kinetic energy:
KE = ½ mv2 or
KE = ½ × m × v2
where:
KE is the kinetic energy in joules, J
m is the mass in kilograms, kg
v is the speed in metres per second, m/s
For example, what is the kinetic energy of a 1000 kg car travelling at 5 m/s?
KE = ½ × 1000 × 25 = 500 × 25 = 12500 J
Given below is a video to help you understand how to use the Kinetic Energy and GPE formula.
Chapter 15
Energy Sources
There are numerous types of energy that is used. They are either classified as renewable or non-renewable resources of energy. Go to the link below to read on the different energy resources.
https://www.nrdc.org/stories/renewable-energy-clean-facts
https://www.nrdc.org/stories/renewable-energy-clean-facts
Energy use
Nearly everything requires energy and a way to use energy is by transferring it from one energy store to another. Systems that can store large amounts of energy are called energy resources. The major energy resources available to produce electricity are fossil fuels, nuclear fuel, biofuel, wind, hydroelectricity, geothermal, tidal, water waves and the Sun.
Energy is needed in:
However, producing and distributing electricity can cause damage to the environment. Releasing energy from some stores causes pollution and harmful waste products. Burning fossil fuels releases carbon dioxide, adding to the greenhouse effect, and sulfur dioxide which causes acid rain.
Patterns and trends in use of energy resources. During the Industrial Revolution, advances in automation and transport caused a significant increase in the amount of fossil fuels extracted and burnt.
In the 20th century, electricity became a convenient way of distributing energy that can be used for a wide range of devices and applications such as lighting, heating, computing technologies and operating machinery.
Demand for energy varies with the time of year and the time of day. During early evenings a lot of energy is needed for heating, lighting and cooking but overnight there is very little needed while people sleep. During winter there is more heating and lighting required than in summertime.
Global energy consumption
Nearly everything requires energy and a way to use energy is by transferring it from one energy store to another. Systems that can store large amounts of energy are called energy resources. The major energy resources available to produce electricity are fossil fuels, nuclear fuel, biofuel, wind, hydroelectricity, geothermal, tidal, water waves and the Sun.
Energy is needed in:
- homes - for cooking, heating and running appliances
- public services, eg schools and hospitals - running machinery and warm rooms
- factories and farms - operating heavy-duty machines and production chains
- transport - buses, trains, cars and boats all need a fuel source, and some trains and trams connect to an electricity supply
However, producing and distributing electricity can cause damage to the environment. Releasing energy from some stores causes pollution and harmful waste products. Burning fossil fuels releases carbon dioxide, adding to the greenhouse effect, and sulfur dioxide which causes acid rain.
Patterns and trends in use of energy resources. During the Industrial Revolution, advances in automation and transport caused a significant increase in the amount of fossil fuels extracted and burnt.
In the 20th century, electricity became a convenient way of distributing energy that can be used for a wide range of devices and applications such as lighting, heating, computing technologies and operating machinery.
Demand for energy varies with the time of year and the time of day. During early evenings a lot of energy is needed for heating, lighting and cooking but overnight there is very little needed while people sleep. During winter there is more heating and lighting required than in summertime.
Global energy consumption
Most of the electricity generated globally is still produced by fossil fuels. This is partly due to:
- the high power output fossil fuels give compared to other energy resources, like wind and water waves
- the existing infrastructure for extracting, transporting and processing fossil fuels - this makes fossil fuels cheaper than setting up new alternatives
n some developed countries, nuclear power stations are a growing form of electricity generation. Nuclear fuel can release large amounts of energy compared to fossil fuels and does not emit carbon dioxide. However, the radioactive waste that is produced is difficult to store and dispose of.
Other factors that could influence governments’ decisions about the use of energy resources are political and economic pressures. For example, countries like Saudi Arabia, whose economy is heavily based in extracting and exporting oil, have a strong interest in fossil fuels to be largely used in electricity generation. In order to compete with more developed countries, growing countries like China need a large power output to keep growing their industry. This means they are likely to continue using fossil fuels and developing the use of nuclear power.
Energy resources
There are different energy resources in the world and the amount of energy stored by them varies greatly. For example, the amount of nuclear energy stored within 1 kg of uranium is enormous, but the gravitational potential energy stored by many thousands of tonnes of water held back by a dam is less.
Renewable resources are replenished either by:
- human action - eg trees cut down for biofuel are replaced by planting new trees
- natural processes - eg water let through a dam for hydroelectricity is replaced through the water cycle.
A non-renewable energy resource is one that is not being replenished as it is being used. It will eventually run out when all reserves have been used up. Different energy sources. The table below shows the main features of the most common energy resources used today.
Comparing resources
Power stations that use fossil fuels or nuclear fuel are very reliable sources of energy. These two types of stations provide much of the UK’s electricity. They operate almost continuously. When additional power is needed, gas power stations are usually used because they will come on very quickly and start generating electricity almost immediately.
The fuel for nuclear power stations is relatively cheap, but the power stations themselves are expensive to build. It is also very expensive to dismantle, or decommission, old nuclear power stations at the end of their useful life. The highly radioactive waste needs to be stored for millions of years before the natural activity will reduce to a safe level.
Water power eg tidal and hydroelectricity are reliable and predictable because of the Moon causing the tides and rainfall filling reservoirs. These two types can also be used to supply additional demand. But many of the renewable sources are unreliable, including wind and solar energy, and cannot respond to increased demand - sunny and windy weather cannot be guaranteed.
Renewable resources have no fuel costs, but the equipment used is expensive to build.
Power stations that use fossil fuels or nuclear fuel are very reliable sources of energy. These two types of stations provide much of the UK’s electricity. They operate almost continuously. When additional power is needed, gas power stations are usually used because they will come on very quickly and start generating electricity almost immediately.
The fuel for nuclear power stations is relatively cheap, but the power stations themselves are expensive to build. It is also very expensive to dismantle, or decommission, old nuclear power stations at the end of their useful life. The highly radioactive waste needs to be stored for millions of years before the natural activity will reduce to a safe level.
Water power eg tidal and hydroelectricity are reliable and predictable because of the Moon causing the tides and rainfall filling reservoirs. These two types can also be used to supply additional demand. But many of the renewable sources are unreliable, including wind and solar energy, and cannot respond to increased demand - sunny and windy weather cannot be guaranteed.
Renewable resources have no fuel costs, but the equipment used is expensive to build.
Homework!
On a word document, summarize the types of energies in a table listing out their advantages and disadvantages. Send all your homeowrk to this e-mail: [email protected]
On a word document, summarize the types of energies in a table listing out their advantages and disadvantages. Send all your homeowrk to this e-mail: [email protected]
Chapter 16
Pressure
Pressure is the force per unit area. This means that the pressure a solid object exerts on another solid surface is its weight in newtons divided by its area in square metres.
P=F/A
where:
p is the unit of pressure in pascals. One pascal is 1 N/m2
f is the unit of force in newtons
a is the unit of area in m2
Area is calculated by the following equation:
area = length × width
The units of length and width are metres.
Question: A force of 20 N acts over an area of 2 m2. What is the pressure?
P= 20 N/ 2m2
P= 10 Pa
To increase pressure - increase the force or reduce the area the force acts on. To cut up your dinner you can either press harder on your knife or use a sharper one (sharper knives have less surface area on the cutting edge of the blade).
To reduce pressure - decrease the force or increase the area the force acts on. If you were standing on a frozen lake and the ice started to crack you could lie down to increase the area in contact with the ice. The same force (your weight) would apply, spread over a larger area, so the pressure would reduce. Snow shoes work in the same way.
Pressure in fluids
Liquids and gases are both called fluids because they are both capable of flowing. The pressure in fluids that are at rest acts equally in all directions.
Barometers
Barometers can be used to predict the weather. They measure changes in atmospheric pressure over time. Differences in pressure are seen on weather forecast maps as a pattern of isobars. These changes in pressure are used to make predictions and, if used with wind readings, are reasonably accurate.
Many traditional barometers contain mercury. The mercury is in a long glass tube with an open reservoir at the bottom:
P=F/A
where:
p is the unit of pressure in pascals. One pascal is 1 N/m2
f is the unit of force in newtons
a is the unit of area in m2
Area is calculated by the following equation:
area = length × width
The units of length and width are metres.
Question: A force of 20 N acts over an area of 2 m2. What is the pressure?
P= 20 N/ 2m2
P= 10 Pa
To increase pressure - increase the force or reduce the area the force acts on. To cut up your dinner you can either press harder on your knife or use a sharper one (sharper knives have less surface area on the cutting edge of the blade).
To reduce pressure - decrease the force or increase the area the force acts on. If you were standing on a frozen lake and the ice started to crack you could lie down to increase the area in contact with the ice. The same force (your weight) would apply, spread over a larger area, so the pressure would reduce. Snow shoes work in the same way.
Pressure in fluids
Liquids and gases are both called fluids because they are both capable of flowing. The pressure in fluids that are at rest acts equally in all directions.
Barometers
Barometers can be used to predict the weather. They measure changes in atmospheric pressure over time. Differences in pressure are seen on weather forecast maps as a pattern of isobars. These changes in pressure are used to make predictions and, if used with wind readings, are reasonably accurate.
Many traditional barometers contain mercury. The mercury is in a long glass tube with an open reservoir at the bottom:
- higher atmospheric pressure exerts a downward force on the mercury in the reservoir - and pushes the mercury up the tube
- lower atmospheric pressure cannot hold up the weight of the mercury column as effectively - so the mercury moves lower down the tube
Depth and pressure in liquids
Pressure increases as you move away from a liquid’s surface. This is seen in the experiment shown in the diagram below. Three identically-sized holes are drilled in a bucket. The pressure is greater at the bottom of the bucket so the water leaves with greater force. This is the reason dams are thicker at the bottom.
Pressure increases as you move away from a liquid’s surface. This is seen in the experiment shown in the diagram below. Three identically-sized holes are drilled in a bucket. The pressure is greater at the bottom of the bucket so the water leaves with greater force. This is the reason dams are thicker at the bottom.
In addition, more dense liquids exert a greater pressure. For example, the pressure recorded at the bottom of a test tube of mercury is greater than the same tube filled with water because mercury is denser.
Pressure differences
When we measure the pressure of gases, like that of the air in car tyres, we usually make this measurement relative to normal air pressure. That is, we calculate the difference between the pressure in the tyre and the pressure exerted by our atmosphere. Liquids can also be measured against normal air pressure.
A manometer measures the pressure acting on a column of fluid. It is made from a U-shaped tube of liquid in which the difference in pressure acting on the two straight sections of the tube causes the liquid to reach different heights in the two arms.
The pressure difference can then be calculated by using the following equation:
pressure difference = height × density × g
p = h × p × g
When we measure the pressure of gases, like that of the air in car tyres, we usually make this measurement relative to normal air pressure. That is, we calculate the difference between the pressure in the tyre and the pressure exerted by our atmosphere. Liquids can also be measured against normal air pressure.
A manometer measures the pressure acting on a column of fluid. It is made from a U-shaped tube of liquid in which the difference in pressure acting on the two straight sections of the tube causes the liquid to reach different heights in the two arms.
The pressure difference can then be calculated by using the following equation:
pressure difference = height × density × g
p = h × p × g
Answer the past paper quesions and send it to this e-mail: [email protected]
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Chapter 17-18 Simple Kinetic Molecular Model of Matter
The kinetic particle theory explains the properties of solids, liquids and gases. There are energy changes when changes in state occur. Brownian motion is the random movement of fluid particles.
Kinetic particle theory
The kinetic particle theory explains the properties of the different states of matter. The particles in solids, liquids and gases have different amounts of energy. They are arranged differently and move in different ways. The table summarises the arrangement and movement of the particles in solids, liquids and gases, and shows simple diagrams for the arrangement of these particles.
Particle arrangement and movement
Kinetic particle theory
The kinetic particle theory explains the properties of the different states of matter. The particles in solids, liquids and gases have different amounts of energy. They are arranged differently and move in different ways. The table summarises the arrangement and movement of the particles in solids, liquids and gases, and shows simple diagrams for the arrangement of these particles.
Particle arrangement and movement
Temperature and pressure in gases
Molecules of a gas move randomly. In a sealed container they exert a force when they collide with the container walls and this applies a pressure to the container. The force and the pressure is equal throughout the container.
Molecules of a gas move randomly. In a sealed container they exert a force when they collide with the container walls and this applies a pressure to the container. The force and the pressure is equal throughout the container.
When gases in containers are heated, their molecules increase in average speed. This means that they exert a greater force when they collide with the container walls, and also collide with the walls more frequently.
The gas is therefore under greater pressure when its temperature is higher. This is why fires near sealed gas cylinders are extremely dangerous. If the cylinders heat up enough, their pressure will increase and they will explode.
The gas is therefore under greater pressure when its temperature is higher. This is why fires near sealed gas cylinders are extremely dangerous. If the cylinders heat up enough, their pressure will increase and they will explode.
The Gas laws
Boyle’s law
Decreasing the volume of a gas increases the pressure of the gas. An example of this is when a gas is trapped in a cylinder by a piston. If the piston is pushed in, the gas particles will have less room to move as the volume the gas occupies has been decreased.
Boyle’s law
Decreasing the volume of a gas increases the pressure of the gas. An example of this is when a gas is trapped in a cylinder by a piston. If the piston is pushed in, the gas particles will have less room to move as the volume the gas occupies has been decreased.
Because the volume has decreased, the particles will collide more frequently with the walls of the container. Each time they collide with the walls they exert a force on them. More collisions mean more force, so the pressure will increase. When the volume decreases, the pressure increases. This shows that the pressure of a gas is inversely proportional to its volume.
This is shown by the following equation - which is often called Boyle’s law. It is named after 17th century scientist Robert Boyle.
P1V1 = P2V2
where:
P1 is the initial pressure
V1 is the initial volume
P2 is the final pressure
V2 is the final volume
It can also be written as:
pressure1 × volume1 = pressure2 × volume2
Note that volume is measured in metres cubed (m3) and temperature in kelvin (K).
It means that for a gas at a constant temperature, pressure × volume is also constant. So increasing pressure from pressure1 to pressure2 means that volume1 will change to volume2, providing the temperature remains constant.
This is shown by the following equation - which is often called Boyle’s law. It is named after 17th century scientist Robert Boyle.
P1V1 = P2V2
where:
P1 is the initial pressure
V1 is the initial volume
P2 is the final pressure
V2 is the final volume
It can also be written as:
pressure1 × volume1 = pressure2 × volume2
Note that volume is measured in metres cubed (m3) and temperature in kelvin (K).
It means that for a gas at a constant temperature, pressure × volume is also constant. So increasing pressure from pressure1 to pressure2 means that volume1 will change to volume2, providing the temperature remains constant.
Charles’ law
Charles’ law describes the effect of changing temperature on the volume of a gas at constant pressure. It states that:
v1= v2(t1/t2)
where:
V1 is the initial volume
V2 is the final volume
T1 is the initial temperature
T2 is the final temperature
Note that volume is measured in metres cubed (m3) and temperature in kelvin (K). This means that if a gas is heated up and the pressure does not change, the volume will. So for a fixed mass of gas at a constant pressure, volume ÷ temperature remains the same.
Charles’ law describes the effect of changing temperature on the volume of a gas at constant pressure. It states that:
v1= v2(t1/t2)
where:
V1 is the initial volume
V2 is the final volume
T1 is the initial temperature
T2 is the final temperature
Note that volume is measured in metres cubed (m3) and temperature in kelvin (K). This means that if a gas is heated up and the pressure does not change, the volume will. So for a fixed mass of gas at a constant pressure, volume ÷ temperature remains the same.
Download the power point presentations below to help enrich your understanding. Watching the videos below too will help.
physics_12_-_simple_kinetic_molecular_model_of_matter_-_1.pptx | |
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physics_13_-_simple_kinetic_molecular_model_of_matter_-_2.pptx | |
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Chapter 19-22 Thermal Properties and temperature 2019
Temperature scales
The most commonly used measurement of temperature is the Celsius scale. The units of this scale are degrees Celsius (°C). This scale was designed to reference the freezing point (0°C) and the boiling point (100°C) of water. There is no upper limit, but the lowest temperature possible is -273°C. At this temperature, almost all matter is solid and the vibrations of particles are incredibly small. Absolute zero is the coldest temperature possible. At absolute zero, all the particles in a substance stop moving. They have no energy left to lose, so the substance cannot get any colder.
Many scientists use the Kelvin scale instead. Kelvin is a better scale to use in space where there is no water. Kelvin begins at absolute zero and so there are no minus numbers in the Kelvin scale, which makes calculations simpler. The units are kelvin (K). An increase in one degree Celsius is the same as one kelvin.
Conversion between the scales:
temperature in degrees Celsius (°C) = temperature in kelvin - 273
temperature in kelvin = temperature in degrees Celsius (°C) + 273
The most commonly used measurement of temperature is the Celsius scale. The units of this scale are degrees Celsius (°C). This scale was designed to reference the freezing point (0°C) and the boiling point (100°C) of water. There is no upper limit, but the lowest temperature possible is -273°C. At this temperature, almost all matter is solid and the vibrations of particles are incredibly small. Absolute zero is the coldest temperature possible. At absolute zero, all the particles in a substance stop moving. They have no energy left to lose, so the substance cannot get any colder.
Many scientists use the Kelvin scale instead. Kelvin is a better scale to use in space where there is no water. Kelvin begins at absolute zero and so there are no minus numbers in the Kelvin scale, which makes calculations simpler. The units are kelvin (K). An increase in one degree Celsius is the same as one kelvin.
Conversion between the scales:
temperature in degrees Celsius (°C) = temperature in kelvin - 273
temperature in kelvin = temperature in degrees Celsius (°C) + 273
To be able to measure temperature easily we require fixed points. Two common fixed points are the melting and boiling points of water. These are 0°C and 100°C respectively.
Thermometers measure temperature. The liquid (usually mercury or coloured alcohol) expands when heated which means that it rises up the glass to show a higher temperature.
Thermometers measure temperature. The liquid (usually mercury or coloured alcohol) expands when heated which means that it rises up the glass to show a higher temperature.
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A thermocouple is used to measure very high temperatures or those that change quickly. Thermocouples contain two different metals. A voltage is produced where these metals meet inside the thermocouple. This voltage is directly related to temperature.
Thermal capacity
The thermal capacity of an object is the amount of heat required to change the temperature of the object by a certain amount. This is measured in joules per kelvin (J/K). The thermal capacity of a block of copper can be determined by heating it and dividing the heat energy used by its temperature change.
Thermal capacity
The thermal capacity of an object is the amount of heat required to change the temperature of the object by a certain amount. This is measured in joules per kelvin (J/K). The thermal capacity of a block of copper can be determined by heating it and dividing the heat energy used by its temperature change.
Specific heat capacity
Heating materials
When materials are heated, the molecules gain kinetic energy and start moving faster. The result is that the material gets hotter.
Different materials require different amounts of energy to change temperature. The amount of energy needed depends on:
It takes less energy to raise the temperature of a block of aluminium by 1°C than it does to raise the same amount of water by 1°C. The amount of energy required to change the temperature of a material depends on the specific heat capacity of the material.
Heat capacity
The specific heat capacity of water is 4,200 Joules per kilogram per degree Celsius (J/kg°C). This means that it takes 4,200 J to raise the temperature of 1 kg of water by 1 °C
Some other examples of specific heat capacities are:
Heating materials
When materials are heated, the molecules gain kinetic energy and start moving faster. The result is that the material gets hotter.
Different materials require different amounts of energy to change temperature. The amount of energy needed depends on:
- the mass of the material
- the substance of the material (specific heat capacity)
- the desired temperature change
It takes less energy to raise the temperature of a block of aluminium by 1°C than it does to raise the same amount of water by 1°C. The amount of energy required to change the temperature of a material depends on the specific heat capacity of the material.
Heat capacity
The specific heat capacity of water is 4,200 Joules per kilogram per degree Celsius (J/kg°C). This means that it takes 4,200 J to raise the temperature of 1 kg of water by 1 °C
Some other examples of specific heat capacities are:
Lead will warm up and cool down fastest because it doesn’t take much energy to change its temperature. Brick will take much longer to heat up and cool down. This is why bricks are sometimes used in storage heaters as they stay warm for a long time. Most heaters are filled with oil (1,800 J/kg°C) or water (4,200 J/kg°C) as these emit a lot of energy as they cool down and, therefore, stay warm for a long time.
Calculating thermal Energy Changes
The amount of thermal energy stored or released as the temperature of a system changes can be calculated using the equation:
change in thermal energy = mass × specific heat capacity × temperature change
ΔEt= mC∆θ
This is when:
Sadie is experimenting with a model steam engine. Before the 0.25 kg of water begins to boil it needs to be heated from 20°C up to 100°C. If the specific heat capacity of water is 4,180 J/kg°C, how much thermal energy is needed to get the water up to boiling point?
ΔEt= mC∆θ
= (0.25)(4180)(100-20)
= 83,600
The video below will help enrich the lessons on solving heat capacity.
The amount of thermal energy stored or released as the temperature of a system changes can be calculated using the equation:
change in thermal energy = mass × specific heat capacity × temperature change
ΔEt= mC∆θ
This is when:
- change in thermal energy (ΔEt) is measured in joules (J)
- mass (m) is measured in kilograms (kg)
- specific heat capacity (c) is measured in joules per kilogram per degree Celsius (J/kg°C)
- temperature change (∆θ) is measured in degrees Celsius (°C)
Sadie is experimenting with a model steam engine. Before the 0.25 kg of water begins to boil it needs to be heated from 20°C up to 100°C. If the specific heat capacity of water is 4,180 J/kg°C, how much thermal energy is needed to get the water up to boiling point?
ΔEt= mC∆θ
= (0.25)(4180)(100-20)
= 83,600
The video below will help enrich the lessons on solving heat capacity.
Required practical - Measuring Specific Heat Capacity
There are different ways to investigate methods of insulation. In this practical activity, it is important to:
Aim of the experiment
To measure the specific heat capacity of a sample of material.
Method
Record results in a suitable table. The example below shows some sample results.
There are different ways to investigate methods of insulation. In this practical activity, it is important to:
- make and record potential difference, current and time accurately
- measure and observe the change in temperature and energy transferred
- use appropriate apparatus and methods to measure the specific heat capacity of a sample of material
Aim of the experiment
To measure the specific heat capacity of a sample of material.
Method
- Place the immersion heater into the central hole at the top of the block.
- Place the thermometer into the smaller hole and put a couple of drops of oil into the hole to make sure the thermometer is surrounded by hot material.
- Fully insulate the block by wrapping it loosely with cotton wool.
- Record the temperature of the block.
- Connect the heater to the power supply and turn it off after ten minutes.
- After ten minutes the temperature will still rise even though the heater has been turned off and then it will begin to cool. Record the highest temperature that it reaches and calculate the temperature rise during the experiment.
Record results in a suitable table. The example below shows some sample results.
Analysis
The block has a mass of 1 kg and the heater was running for 10 minutes = 600 seconds.
Using the example results:
energy transferred = potential difference × current × time
The block has a mass of 1 kg and the heater was running for 10 minutes = 600 seconds.
Using the example results:
energy transferred = potential difference × current × time
The actual value for the specific heat capacity of aluminium is 900 J/kg°C. The calculated value does not match exactly but it is in the correct order of magnitude.
Evaluation
Evaluation
- All experiments are subject to some amount of experimental error due to inaccurate measurement, or variables that cannot be controlled. In this case, not all of the heat from the immersion heater will be heating up the aluminium block, some will be lost to the surroundings.
- More energy has been transferred than is needed for the block alone as some is transferred to the surroundings. This causes the calculated specific heat capacity to be higher than for 1 kg of aluminium alone.
Chapter 23-24
Specific Latent Heat and Thermal Process
Specific latent heat is the amount of energy required to change the state of 1 kilogram (kg) of a material without changing its temperature.As there are two boundaries, solid/liquid and liquid/gas, each material has two specific latent heats:
Some typical values for specific latent heat include:
- latent heat of fusion - the amount of energy needed to freeze or melt the material at its melting point
- latent heat of vaporisation - the amount of energy needed to evaporate or condense the material at its boiling point
Some typical values for specific latent heat include:
An input of 334,000 joules (J) of energy is needed to change 1 kg of ice into 1 kg of water. The same amount of energy needs to be taken out of the liquid to freeze it.
Calculating thermal energy changes
The amount of thermal energy stored or released as the temperature of a system changes can be calculated using the equation:
change in thermal energy = mass × specific latent heat
Et= ml
This is when:
Calculating thermal energy changes
The amount of thermal energy stored or released as the temperature of a system changes can be calculated using the equation:
change in thermal energy = mass × specific latent heat
Et= ml
This is when:
- change in thermal energy (ΔEt) is measured in joules (J)
- mass (m) is measured in kilograms (kg)
- specific latent heat (l) is measured in joules per kilogram (J/kg)
Measuring latent heat
Latent heat can be measured from a heating or cooling curve line graph. If a heater of known power is used, such as a 60 W immersion heater that provides 60 J/s, the temperature of a known mass of ice can be monitored each second. This will generate a graph that looks like this.
Latent heat can be measured from a heating or cooling curve line graph. If a heater of known power is used, such as a 60 W immersion heater that provides 60 J/s, the temperature of a known mass of ice can be monitored each second. This will generate a graph that looks like this.
The graph is horizontal at two places. These are the places where the energy is not being used to increase the speed of the particles, increasing temperature, but is being used to break the bonds between the particles to change the state.
The longer the horizontal line, the more energy has been used to cause the change of state. The amount of energy represented by these horizontal lines is equal to the latent heat.
Example. If a horizontal line that shows boiling on a heating curve is 1 hour 3 minutes long, how much energy has a 60 watts (W) heater provided to the water?
63 minutes = 3,780 s
60 W means 60 J of energy is supplied every second
energy = power × time
energy= (60)(3780)
energy= 226,800 J
Example 2 .If this energy had been applied to 100 g of water, what is the latent heat of vaporisation of water?
226,800 J for 100 g is equivalent to 2,268,000 J for 1 kg. The latent heat of vaporisation of water is 2,268,000 J/kg.
The longer the horizontal line, the more energy has been used to cause the change of state. The amount of energy represented by these horizontal lines is equal to the latent heat.
Example. If a horizontal line that shows boiling on a heating curve is 1 hour 3 minutes long, how much energy has a 60 watts (W) heater provided to the water?
63 minutes = 3,780 s
60 W means 60 J of energy is supplied every second
energy = power × time
energy= (60)(3780)
energy= 226,800 J
Example 2 .If this energy had been applied to 100 g of water, what is the latent heat of vaporisation of water?
226,800 J for 100 g is equivalent to 2,268,000 J for 1 kg. The latent heat of vaporisation of water is 2,268,000 J/kg.
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Conduction
Heat is thermal energy. It can be transferred from one place to another by conduction. Metals are good conductors of heat, but non-metals and gases are usually poor conductors. Poor conductors are called insulators. Heat energy is conducted from the hot end of an object to the cold end.
Conduction in metals.
The electrons in a piece of metal can leave their atoms and move about in the metal as free electrons. The parts of the metal atoms left behind are now positively charged metal ions. The ions are packed closely together and they vibrate continually. The hotter the metal, the more kinetic energy these vibrations have. This kinetic energy is transferred from hot parts of the metal to cooler parts by the free electrons.
These move through the structure of the metal, colliding with ions as they go.
Heat is thermal energy. It can be transferred from one place to another by conduction. Metals are good conductors of heat, but non-metals and gases are usually poor conductors. Poor conductors are called insulators. Heat energy is conducted from the hot end of an object to the cold end.
Conduction in metals.
The electrons in a piece of metal can leave their atoms and move about in the metal as free electrons. The parts of the metal atoms left behind are now positively charged metal ions. The ions are packed closely together and they vibrate continually. The hotter the metal, the more kinetic energy these vibrations have. This kinetic energy is transferred from hot parts of the metal to cooler parts by the free electrons.
These move through the structure of the metal, colliding with ions as they go.
Investigating conductors
An experiment can be used to investigate which metal is the best conductor of heat. It involves some long thin strips of different metals (eg steel, aluminium and copper), wax, drawing pins and a Bunsen burner.
Method:
- Fix the drawing pin to the end of the metal strip using drops of wax.
- Position the other end of the metal strip into a Bunsen flame.
- Record the time taken for the wax to melt and the drawing pin to drop off.
The fastest time shows the best conductor of heat.
Variables that affect the time taken for the drawing pins to fall include the distance they are from the flame and the thickness of the metal. If you have controlled all of these variables, you should find that copper conducts better than aluminium, while aluminium conducts better than steel.
Convection
Heat can be transferred from one place to another by convection.
Fluids
Liquids and gases are fluids because they can be made to flow. The particles in these fluids can move from place to place. Convection occurs when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy. Heat energy is transferred from hot places to cooler places by convection.
Liquids and gases expand when they are heated. This is because the particles in liquids and gases move faster when they are heated than they do when they are cold. As a result, the particles take up more volume. This is because the gap between particles widens, while the particles themselves stay the same size. The liquid or gas in hot areas is less dense than the liquid or gas in cold areas, so it rises into the cold areas. The denser cold liquid or gas falls into the warm areas.
In this way, convection currents that transfer heat from place to place are set up. Convection currents can be seen in lava lamps. The wax inside the lamp warms up, becomes less dense than the liquid and so rises. When it rises, it cools and becomes denser again, so it sinks. This same effect can be seen by putting a crystal of potassium permanganate in a beaker of water and gently heating it.
Convection explains why hot air balloons rise, and also why it is often hotter in the lofts of houses than downstairs. As well as these examples, convection is seen on a much bigger scale in our weather and ocean currents.
Heat transfer by radiation
Heat can be transferred by infrared radiation. Unlike conduction and convection - which need particles - infrared radiation is a type of electromagnetic radiation that involves waves.
Because no particles are involved, radiation can even work through the vacuum of space. This is why we can still feel the heat of the Sun even though it is 150 million km away from the Earth.
Different surfaces
Some surfaces are better than others at reflecting and absorbing infrared radiation. This table summarises some differences:
Heat can be transferred by infrared radiation. Unlike conduction and convection - which need particles - infrared radiation is a type of electromagnetic radiation that involves waves.
Because no particles are involved, radiation can even work through the vacuum of space. This is why we can still feel the heat of the Sun even though it is 150 million km away from the Earth.
Different surfaces
Some surfaces are better than others at reflecting and absorbing infrared radiation. This table summarises some differences:
You can see that dull surfaces are good absorbers and emitters of infrared radiation. Shiny surfaces are poor absorbers and emitters (but they are good reflectors of infrared radiation).
If two objects made from the same material have identical volumes, a thin, flat object will radiate heat energy faster than a fat object.
This is one reason why domestic radiators are thin and flat.
Radiators are often painted with gloss paint, but they would be better at radiating heat if they were painted with matt paint instead. Also, despite their name, radiators actually transfer most of their heat to a room by convection, not radiation.
Heat radiation investigation. The transfer of infrared radiation from a hot object to cooler surroundings can be investigated using a piece of apparatus called Leslie’s cube.This is a metal cube with four side prepared in different ways: black, white, shiny, or dull. It can be filled with hot water or heated on an electrical hot plate so that all four sides are at the same temperature.
Method
If two objects made from the same material have identical volumes, a thin, flat object will radiate heat energy faster than a fat object.
This is one reason why domestic radiators are thin and flat.
Radiators are often painted with gloss paint, but they would be better at radiating heat if they were painted with matt paint instead. Also, despite their name, radiators actually transfer most of their heat to a room by convection, not radiation.
Heat radiation investigation. The transfer of infrared radiation from a hot object to cooler surroundings can be investigated using a piece of apparatus called Leslie’s cube.This is a metal cube with four side prepared in different ways: black, white, shiny, or dull. It can be filled with hot water or heated on an electrical hot plate so that all four sides are at the same temperature.
Method
- Measure the temperature a fixed distance from each side of a Leslie's cube using thermometers (or using a thermocouple, an electrical device that produces a potential difference depending on the temperature).
- Heat the Leslie’s cube with boiling water or with a hot plate.
- Continue to measure and record the temperatures every 30 seconds for five minutes, then plot a graph of temperature against time for each side.
- Compare the four graphs obtained. Remember that the four thermometers may vary in accuracy, so take this into account when analysing the results.
Reducing heat transfers – houses
Heat energy is lost from buildings through their roofs, windows, walls, floors and through gaps around windows and doors. However, there are ways that these losses can be reduced.
Heat energy is transferred from homes by conduction through the walls, floor, roof and windows. It is also transferred from homes by convection. For example, cold air can enter the house through gaps in doors and windows, and convection currents can transfer heat energy in the loft to the roof tiles.
Heat energy also leaves the house by radiation - through the walls, roof and windows.
Ways to reduce heat lossThere are several different ways to reduce heat loss:
Watch the video below to help enrich your understanding on these chapters.
Heat energy is lost from buildings through their roofs, windows, walls, floors and through gaps around windows and doors. However, there are ways that these losses can be reduced.
Heat energy is transferred from homes by conduction through the walls, floor, roof and windows. It is also transferred from homes by convection. For example, cold air can enter the house through gaps in doors and windows, and convection currents can transfer heat energy in the loft to the roof tiles.
Heat energy also leaves the house by radiation - through the walls, roof and windows.
Ways to reduce heat lossThere are several different ways to reduce heat loss:
- Simple ways to reduce heat loss include fitting carpets, curtains and draught excluders. It is even possible to fit reflective foil in the walls or on them.
- Heat loss through windows can be reduced by using double glazing. These special windows have air or a vacuum between two panes of glass. If the double glazing has a vacuum there will be no conduction or convection. If the double glazing is made with air between the glass then convection is minimised because there is little room for the air to move. Air is a poor conductor so there will be very little heat loss by conduction.
- Heat loss through walls can be reduced using cavity wall insulation. This involves blowing insulating material into the gap between the brick and the inside wall. Insulating materials are bad conductors and so this reduces the heat loss by conduction. The material also prevents air circulating inside the cavity, therefore reducing heat loss by convection.
- Heat loss through the roof can be reduced by laying loft insulation. This works in a similar way to cavity wall insulation.
Watch the video below to help enrich your understanding on these chapters.
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Section 3 Properties of waves
Chapter 25 Mechanical Waves
Waves
Waves are one of the ways in which energy may be transferred between stores. Waves can be described as oscillations, or vibrations about a rest position. For example:
The direction of these oscillations is the difference between longitudinal or transverse waves. In longitudinal waves, the vibrations are parallel to the direction of wave travel. In transverse waves, the vibrations are at right angles to the direction of wave travel. Mechanical waves cause oscillations of particles in a solid, liquid or gas and must have a medium to travel through. Electromagnetic waves cause oscillations in electrical and magnetic fields.
Parts of a wave
Waves are described using the following terms:
Waves are one of the ways in which energy may be transferred between stores. Waves can be described as oscillations, or vibrations about a rest position. For example:
- sound waves cause air particles to vibrate back and forth
- ripples cause water particles to vibrate up and down
The direction of these oscillations is the difference between longitudinal or transverse waves. In longitudinal waves, the vibrations are parallel to the direction of wave travel. In transverse waves, the vibrations are at right angles to the direction of wave travel. Mechanical waves cause oscillations of particles in a solid, liquid or gas and must have a medium to travel through. Electromagnetic waves cause oscillations in electrical and magnetic fields.
Parts of a wave
Waves are described using the following terms:
- rest position - the undisturbed position of particles or fields when they are not vibrating
- displacement - the distance that a certain point in the medium has moved from its re st position
- peak - the highest point above the rest position
- trough - the lowest point below the rest position
- amplitude - the maximum displacement of a point of a wave from its rest position
- wavelength - distance covered by a full cycle of the wave, usually measured from peak to peak, or trough to trough
- time period - the time taken for a full cycle of the wave, usually measured from peak to peak, or trough to trough
- frequency - the number of waves passing a point each second
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Wave period
The time period of a wave can be calculated using the equation:
t= 1/f
This is when:
Example Calculate the time period of a wave with a frequency of 50 Hz.
t= 1/f
t= 1/50
t= 0.02 Hz
Calculating wave speed
The speed of a wave can be calculated using the equation:
wave speed = frequency × wavelength
v= fλ
This is when:
The time period of a wave can be calculated using the equation:
t= 1/f
This is when:
- the period (T) is measured in seconds (s)
- frequency (f) is measured in hertz (Hz)
Example Calculate the time period of a wave with a frequency of 50 Hz.
t= 1/f
t= 1/50
t= 0.02 Hz
Calculating wave speed
The speed of a wave can be calculated using the equation:
wave speed = frequency × wavelength
v= fλ
This is when:
- wave speed (v) is measured in metres per second (m/s)
- frequency (f) is measured in Hertz (Hz)
- wavelength (λ) is measured in metres (m)
Example
What is the speed of a wave that has a frequency of 50 Hz and a wavelength of 6 m?
v= 50/s x 6m
v= 300 m/s
Measuring the speed of sound in air and water
The air is made up of many tiny particles. When sound is created, the air particles vibrate and collide with each other, causing the vibrations to pass between air particles. The vibrating particles pass the sound through to a person's ear and vibrate the ear drum.
Light travels much faster than sound through air. For example, a person fires a starting pistol and raises their hand in the air at the same time. A distant observer stood 400 metres (m) away records the time between seeing the action (the light reaches the time keeper immediately) and hearing the sound (which takes more time to cover the same distance).
The speed of sound can be calculated using the equation:
V=d/t
This is when:
Example
An observer 400 m away records a 1.2 s time difference between seeing the hand signal and hearing the bang of the starting pistol.
v=d/t
v= 400 m/1.2 s
v= 333.33 m/s
The accepted value for the speed of sound in air is 330 m/s.
However, this experimental method is flawed as humans do not use stop clocks identically to one another. One person might stop the timer a fraction of a second later than another person. The values recorded will be dependent on the reaction time of the observer, and will not be entirely accurate. This explains why the answer of 333 m/s is slightly above the accepted value for the speed of sound in air.
Required practical
Measure the frequency, wavelength and speed of waves in a ripple tank
A ripple tank can be used to measure and calculate frequency, wavelength and the speed of waves on the surface of the water. A ripple tank is a transparent shallow tray of water with a light shining down through it onto a white card below in order to clearly see the motion of the ripples created on the water’s surface. Ripples can be made by hand but to generate regular ripples it is better to use a motor.
What is the speed of a wave that has a frequency of 50 Hz and a wavelength of 6 m?
v= 50/s x 6m
v= 300 m/s
Measuring the speed of sound in air and water
The air is made up of many tiny particles. When sound is created, the air particles vibrate and collide with each other, causing the vibrations to pass between air particles. The vibrating particles pass the sound through to a person's ear and vibrate the ear drum.
Light travels much faster than sound through air. For example, a person fires a starting pistol and raises their hand in the air at the same time. A distant observer stood 400 metres (m) away records the time between seeing the action (the light reaches the time keeper immediately) and hearing the sound (which takes more time to cover the same distance).
The speed of sound can be calculated using the equation:
V=d/t
This is when:
- speed (v) is measured in metres per second (m/s)
- distance (s) is measured in metres (m)
- time (t) is measured in seconds (s)
Example
An observer 400 m away records a 1.2 s time difference between seeing the hand signal and hearing the bang of the starting pistol.
v=d/t
v= 400 m/1.2 s
v= 333.33 m/s
The accepted value for the speed of sound in air is 330 m/s.
However, this experimental method is flawed as humans do not use stop clocks identically to one another. One person might stop the timer a fraction of a second later than another person. The values recorded will be dependent on the reaction time of the observer, and will not be entirely accurate. This explains why the answer of 333 m/s is slightly above the accepted value for the speed of sound in air.
Required practical
Measure the frequency, wavelength and speed of waves in a ripple tank
A ripple tank can be used to measure and calculate frequency, wavelength and the speed of waves on the surface of the water. A ripple tank is a transparent shallow tray of water with a light shining down through it onto a white card below in order to clearly see the motion of the ripples created on the water’s surface. Ripples can be made by hand but to generate regular ripples it is better to use a motor.
Measure the frequency, wavelength and speed of waves in a ripple tank.
Method
Method
- Set up the ripple tank as shown in the diagram with about 5 cm depth of water.
- Adjust the height of the wooden rod so that it just touches the surface of the water.
- Switch on the lamp and motor and adjust until low frequency waves can be clearly observed.
- Measure the length of a number of waves then divide by the number of waves to record wavelength. It may be more practical to take a photograph of the card with the ruler and take measurements from the still picture.
- Count the number of waves passing a point in ten seconds then divide by ten to record frequency.
- Calculate the speed of the waves using: wave speed = frequency × wavelength.
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Refer to the past paper questions on Waves. Download all files and answer them in a word document. After which, send all your files to this e-mail: [email protected]
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Chapters 26 -28
Light, Reflection, and Plane Mirrors
Sources of Light
Light waves are transverse waves, they travel in straight lines so it is 'rectilinear'. It can be reflected, if not we wouldn't be able to see, because light is constantly reflecting off objects into our eyes.
Refer to the link below in order to read on the different sources of light.
https://www.vedantu.com/physics/light-sources
A pin hole camera is used to see how light moves through a medium, air. The image of an object viewed is similar to the object. Watch a video below on how to construct a pin hole camera.
Light waves are transverse waves, they travel in straight lines so it is 'rectilinear'. It can be reflected, if not we wouldn't be able to see, because light is constantly reflecting off objects into our eyes.
Refer to the link below in order to read on the different sources of light.
https://www.vedantu.com/physics/light-sources
A pin hole camera is used to see how light moves through a medium, air. The image of an object viewed is similar to the object. Watch a video below on how to construct a pin hole camera.
Ray diagrams
A ray diagram shows how light travels, including what happens when it reaches a surface.
In a ray diagram, you draw each ray as:
Remember to use a ruler and a sharp pencil.
Investigating the law of reflection
A ray diagram shows how light travels, including what happens when it reaches a surface.
In a ray diagram, you draw each ray as:
- a straight line;
- with an arrowhead pointing in the direction that the light travels.
Remember to use a ruler and a sharp pencil.
Investigating the law of reflection
- On a sheet of white paper draw a pencil line – label this AB.
- Using a protractor, draw a normal at C, roughly the middle of AB.
- Draw a line at 20o to the normal.
- Position a plane mirror carefully along AB.
- Direct a ray of light from a ray box along the 20o line – this is the incident ray. Record the angle of incidence i in a suitable table.
- Use 2 pencil Xs to mark the position of the reflected ray.
- Take away the mirror and join these Xs back to C. This is the reflected ray. Put an arrow on it to show its direction.
- Measure the angle between the normal and the reflected ray with the protractor and record the angle of reflection r in the table.
- Repeat the experiment for a series of incident rays.
Conclusion
When light is reflected by a plane mirror:
the angle of incidence = the angle of reflection.
This is known as the law of reflection.
When light is reflected by a plane mirror:
the angle of incidence = the angle of reflection.
This is known as the law of reflection.
- the hatched vertical line on the left represents the plane mirror;
- the dashed line is called the normal, drawn at 90° to the surface of the mirror;
- the angle of incidence, i, is the angle between the normal and incident ray;
- the angle of reflection, r, is the angle between the normal and reflected ray.
The law of reflection states that: angle of incidence i = angle of reflection r.
For example, if a light ray hits a surface with an angle of incidence of 45°, it will be reflected with an angle of reflection of 45°.
For example, if a light ray hits a surface with an angle of incidence of 45°, it will be reflected with an angle of reflection of 45°.
Investigating the position of an image of a plane mirror
Conclusion
For each position of the object:
- Draw a pencil line across the top of a sheet of white paper. Mark points A and B. Select a position for the object and label that O.
- Use a pencil and ruler to draw an incident ray from O to A and from O to B. Include arrows.
- Use a ray box to direct two rays of light along the lines from object O towards points A and B.
- Mark 2 pencil Xs to mark each of the reflected rays from A and from B.
- Remove the mirror and use a pencil and ruler to join the Xs These represent the reflected rays.
- Extend the reflected rays behind the mirror until they meet at point. This is where the image was formed. Label the point I. These dotted lines are called virtual rays.
- With a 30 cm ruler, measure the perpendicular distance from O to the mirror and from I to the mirror.
- Repeat the experiment for different positions of the object O.
Conclusion
For each position of the object:
- the perpendicular distance of the object O from the mirror equals the perpendicular distance of the image I from the mirror.
- the image is the same distance behind the mirror as the object is in front.
Specular reflection
Reflection from a smooth, flat surface is called specular reflection. This reflection obeys the law of reflection and is the type that happens with a flat mirror.
Properties of the image in a plane mirror
The image in a mirror is:
The image appears to be behind the mirror.
Reflection from a smooth, flat surface is called specular reflection. This reflection obeys the law of reflection and is the type that happens with a flat mirror.
Properties of the image in a plane mirror
The image in a mirror is:
- upright – but left and right are reversed. The image is laterally inverted;
- the same height as the object;
- as far behind the mirror as the object is in front;
- virtual.
The image appears to be behind the mirror.
- A virtual image cannot be formed on a screen.
- It can only be seen by looking into the mirror.
Key point
The image in a plane mirror is:
Diffuse reflection
If a surface is rough, diffuse reflection happens. Instead of forming an image, the reflected light is scattered in all directions. This may cause a distorted image of the object, as occurs with rippling water, or no image at all. Each individual reflection still obeys the law of reflection, but the different parts of the rough surface are at different angles.
The image in a plane mirror is:
- as far behind the mirror as the object is in front;
- upright but laterally inverted;
- same size as the object;
- virtual.
Diffuse reflection
If a surface is rough, diffuse reflection happens. Instead of forming an image, the reflected light is scattered in all directions. This may cause a distorted image of the object, as occurs with rippling water, or no image at all. Each individual reflection still obeys the law of reflection, but the different parts of the rough surface are at different angles.
Chapter 29- 31
Refraction, Total Internal Reflection, Lenses
Refraction of waves
Different materials have different densities. Light waves may change direction at the boundary between two transparent materials. Refraction is the change in direction of a wave at such a boundary. It is important to be able to draw ray diagrams to show the refraction of a wave at a boundary.
Different materials have different densities. Light waves may change direction at the boundary between two transparent materials. Refraction is the change in direction of a wave at such a boundary. It is important to be able to draw ray diagrams to show the refraction of a wave at a boundary.
Refraction can cause optical illusions as the light waves appear to come from a different position to their actual source.
Explaining refraction
The density of a material affects the speed that a wave will be transmitted through it. In general, the denser the transparent material, the more slowly light travels through it. Glass is denser than air, so a light ray passing from air into glass slows down. If the ray meets the boundary at an angle to the normal, it bends towards the normal. The reverse is also true. A light ray speeds up as it passes from glass into air, and bends away from the normal by the same angle.
Explaining refraction
The density of a material affects the speed that a wave will be transmitted through it. In general, the denser the transparent material, the more slowly light travels through it. Glass is denser than air, so a light ray passing from air into glass slows down. If the ray meets the boundary at an angle to the normal, it bends towards the normal. The reverse is also true. A light ray speeds up as it passes from glass into air, and bends away from the normal by the same angle.
Required practical
Investigate refraction in rectangular blocks in terms of the interaction of electromagnetic waves with matterThere are different ways to investigate refraction in rectangular blocks. In this required practical activity, it is important to:
Method
Investigate refraction in rectangular blocks in terms of the interaction of electromagnetic waves with matterThere are different ways to investigate refraction in rectangular blocks. In this required practical activity, it is important to:
- make and record the angles of incidence and the angles of refraction accurately
- measure and observe the angle of refraction
- use appropriate apparatus and methods to measure refraction and how it may be different for different substances
Method
Wave speed, frequency and wavelength in refraction
For a given frequency of light, the wavelength is proportional to the wave speed:
wave speed = frequency × wavelength
So if a wave slows down, its wavelength will decrease. The effect of this can be shown using wave front diagrams like the one below. The diagram shows that as a wave travels into a denser medium, such as water, it slows down and the wavelength decreases. Although the wave slows down, its frequency remains the same, due to the fact that its wavelength is shorter.
For a given frequency of light, the wavelength is proportional to the wave speed:
wave speed = frequency × wavelength
So if a wave slows down, its wavelength will decrease. The effect of this can be shown using wave front diagrams like the one below. The diagram shows that as a wave travels into a denser medium, such as water, it slows down and the wavelength decreases. Although the wave slows down, its frequency remains the same, due to the fact that its wavelength is shorter.
Types of lens
When light is refracted it changes direction due to the change in density as it moves from air into glass or plastic. Lenses are used in cameras, telescopes, binoculars, microscopes and corrective glasses. A lens can be converging (convex) or diverging (concave). Converging (or convex) lensesA converging lens is thicker in the middle than it is at the edges.
Parallel light rays that enter the lens converge.
They come together at a point on the principal axis called the principal focus F. The centre of the lens is called the optical centre C.
A ray of light incident at the optical centre passes straight through without being bent.
When light is refracted it changes direction due to the change in density as it moves from air into glass or plastic. Lenses are used in cameras, telescopes, binoculars, microscopes and corrective glasses. A lens can be converging (convex) or diverging (concave). Converging (or convex) lensesA converging lens is thicker in the middle than it is at the edges.
Parallel light rays that enter the lens converge.
They come together at a point on the principal axis called the principal focus F. The centre of the lens is called the optical centre C.
A ray of light incident at the optical centre passes straight through without being bent.
In a ray diagram, a converging lens is drawn as a vertical line with outward facing arrows to indicate the shape of the lens.
Key point
Key point
- The focal length f of a converging lens is the distance between the optical centre, C, of the lens and the principal focus, F.
- Focal length is measured in m, cm or mm
Investigation: Focal Length
- Point the lens at a distance object outside the window – for instance a tree or building. The greater the distance the better. Rays of light from this object are taken to be parallel as the object is assumed to be at infinity.
- Move the position of the screen behind the lens until a sharp image is formed on it.
- Parallel rays of light form an image at the principal focus of a lens, and so the screen is at the principal focus. The distance between the optical centre of the lens and the screen is the focal length, f.
- Measure this distance with a 30 cm rule and record in a suitable table.
- Repeat the process several times and calculate the average focal length.
Diverging (or Concave) lenses
A diverging lens is thinner in the middle than it is at the edges. This causes parallel rays to diverge. They separate but appear to come from a principle focus F on the other side of the lens.
In a ray diagram, a diverging lens is drawn as a vertical line with inward facing arrows to indicate the shape of the lens.
Real and virtual images
The images formed by a lens can be:
A real image is an image that can be projected onto a screen. Rays of light actually pass through the image. A virtual image cannot be projected onto a screen. It appears to come from behind the lens and can only be seen by looking through the lens. Rays of light appear to come from a virtual image, rather than pass through it.
The images formed by a lens can be:
- upright or inverted (upside down compared to the object);
- enlarged or diminished (smaller than the object);
- real or virtual.
A real image is an image that can be projected onto a screen. Rays of light actually pass through the image. A virtual image cannot be projected onto a screen. It appears to come from behind the lens and can only be seen by looking through the lens. Rays of light appear to come from a virtual image, rather than pass through it.
The human eye and defects of vision
The normal, human eye forms a real, diminished, inverted image on the retina. Most of the refraction occurs at the air – cornea boundary. Light then enters the lens after passing through the pupil. The iris is the coloured part of the eye, surrounding the pupil.
The converging (convex) lens provides the rest of the refraction necessary to focus the rays of light sharply on the light sensitive cells of the retina at the back of the eye.
The ciliary muscles change the shape and hence the focal length of the lens, allowing the eye to focus on both near and far objects.
The normal, human eye forms a real, diminished, inverted image on the retina. Most of the refraction occurs at the air – cornea boundary. Light then enters the lens after passing through the pupil. The iris is the coloured part of the eye, surrounding the pupil.
The converging (convex) lens provides the rest of the refraction necessary to focus the rays of light sharply on the light sensitive cells of the retina at the back of the eye.
The ciliary muscles change the shape and hence the focal length of the lens, allowing the eye to focus on both near and far objects.
Near point
Long Sight
- The closest distance from the unaided eye at which an object can be seen clearly is called the near point.
- The near point is 25cm for a normal, adult eye.
- The furthest distance from the unaided eye at which an object can be seen clearly is called the far point.
- The far point is taken to be infinity for a normal, adult eye.
- The normal, adult, human, eye can see clearly objects at distances of 25cm from the eye to infinity.
- This range is more limited for the very young or as we get older.
Long Sight
- A long-sighted person can see objects a long distance away (they have good long sight) but can’t see objects a short distance away. A long-sighted person can read writing on a whiteboard in a classroom clearly but cannot read print in a book or newspaper sharply.
- Images of nearby objects (at 25cm from the eye) are formed behind the retina. The image is blurred.
- Long sight is due to the eyeball being too short, or the lens cannot be made thick enough by the ciliary muscles to focus the light rays on the retina. Long sight often occurs in older people as the ciliary muscles weaken with age.
Correcting Long Sight
- Rays from a nearby object need to be converged more, to form the image on the retina.
- Long sight is corrected using a converging lens which starts to converge light rays from a nearby object before they enter the eye.
- Converging (convex) lenses are used in reading glasses.
Short Sight
- A short-sighted person can see close objects clearly (they have good short sight), but they can’t see distant objects clearly. A short-sighted person can read a book clearly but cannot read writing on a whiteboard in a classroom or a car number plate at distance.
- The image of a distant object, say 2 m to 3 m from the eye, is formed just in front of the retina, causing it to appear blurred.
- This defect is due to the eyeball being too long or the ciliary muscles cannot make the lens thin enough.
Correcting for short sight
- Rays from a distant object need to be spread out, before they reach the lens.
- Short sight is corrected using a diverging lens which diverges the light rays from a distant object before they enter the eye.
- Diverging (concave) lenses are used in spectacles for distance viewing.
Lens ray diagram
To draw a ray diagram:
Convex lenses
The type of image formed by a convex lens depends on the lens used and the distance from the object to the lens.
A camera or human eye
Cameras and eyes contain convex lenses. For a distant object that is placed more than twice the focal length from the lens, the image is:
To draw a ray diagram:
- Draw a ray from the object to the lens that is parallel to the principal axis. Once through the lens, the ray passes through the principal focus F.
- Draw a ray which passes from the object through the optical centre of the lens. It passes straight through without being bent.
- A third ray can be drawn from the object through F on the same side of the lens, and then to the lens. Once through the lens, the ray passes parallel to the principal axis.
Convex lenses
The type of image formed by a convex lens depends on the lens used and the distance from the object to the lens.
A camera or human eye
Cameras and eyes contain convex lenses. For a distant object that is placed more than twice the focal length from the lens, the image is:
- between F and 2F on the opposite side of the lens to the object;
- inverted;
- diminished;
- real.
Projector
Projectors contain convex lenses. For an object placed between one and two focal lengths from the lens, the image is:
Projectors contain convex lenses. For an object placed between one and two focal lengths from the lens, the image is:
- further away than 2F on the opposite side of the lens to the object;
- inverted;
- enlarged;
- real.
In a film or data projector, this image is formed on a screen. Film must be loaded into the projector upside down so the projected image is the right way up.
Total internal reflection
When a light ray reaches the boundary between two transparent materials it may be refracted. If it is leaving the more dense medium, this refraction would be expected to bend the ray away from the normal as it emerges.
However, if this would bring the ray out at more than 90° from the normal, the refraction is not possible. In this situation, the ray is reflected inside the more dense medium, following the law of reflection.
This is called total internal reflection (TIR). The angle of incidence when the ray changes from just refracting to TIR is called the critical angle.
When a light ray reaches the boundary between two transparent materials it may be refracted. If it is leaving the more dense medium, this refraction would be expected to bend the ray away from the normal as it emerges.
However, if this would bring the ray out at more than 90° from the normal, the refraction is not possible. In this situation, the ray is reflected inside the more dense medium, following the law of reflection.
This is called total internal reflection (TIR). The angle of incidence when the ray changes from just refracting to TIR is called the critical angle.
Uses of total internal reflection (TIR)
Total internal reflection allows light to be contained and guided along very thin fibres. Usually made of glass, these are called optical fibres and they have many uses:
Total internal reflection allows light to be contained and guided along very thin fibres. Usually made of glass, these are called optical fibres and they have many uses:
- fibre broadband internet sends computer information coded as pulses of light along underground optical fibres
- doctors can look at the inside of their patients using an endoscope - a long tube which guides light into the patient and then guides the reflected light back out to give an image
- decorations, like some artificial Christmas trees, carry coloured light to different parts of the decoration and let it shine out in different directions
Final Exam Revision Day 1 to Day 4
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Chapter 49
Radioactivity
Radioactive decay
Stable nuclei
An atom's nucleus can only be stable if it has a certain number of neutrons for the number of protons it has. Elements with fewer protons, such as the ones near the top of the periodic table, are stable if they have the same number of neutrons and protons, for example carbon, carbon-12 is stable and has six protons and six neutrons.
However as the number of protons increases, more neutrons are needed to keep the nucleus stable, for example lead, lead-206 has 82 protons and has 124 neutrons.
Stable nuclei
An atom's nucleus can only be stable if it has a certain number of neutrons for the number of protons it has. Elements with fewer protons, such as the ones near the top of the periodic table, are stable if they have the same number of neutrons and protons, for example carbon, carbon-12 is stable and has six protons and six neutrons.
However as the number of protons increases, more neutrons are needed to keep the nucleus stable, for example lead, lead-206 has 82 protons and has 124 neutrons.
Nuclei with too many, or too few, neutrons do exist naturally but are unstable and will decay, in a random process, emitting radiation.
Types of radioactive decay
An unstable nucleus can decay by emitting an alpha particle, a ß- (beta minus) particle, a ß+ (positron), a gamma ray or in some cases a single neutron.
Alpha particle
If the nucleus is unstably large, it will emit a 'package' of two protons and two neutrons called an alpha particle.
Types of radioactive decay
An unstable nucleus can decay by emitting an alpha particle, a ß- (beta minus) particle, a ß+ (positron), a gamma ray or in some cases a single neutron.
Alpha particle
If the nucleus is unstably large, it will emit a 'package' of two protons and two neutrons called an alpha particle.
An alpha particle is also a helium-4 nucleus, so it is written as 42He. It is also sometimes written as 42α. Alpha decay causes the mass number of the nucleus to decrease by four and the atomic number of the nucleus to decrease by two.
Beta minus decay
If the nucleus has too many neutrons, a neutron will turn into a proton and emit a fast-moving electron. This electron is called a beta minus (β-) particle - this process is known as beta radiation. A beta particle has a relative mass of zero, so its mass number is zero. As the beta particle is an electron, it can be written as 0-1e. However, sometimes it is also written as 0-1β. The beta particle is an electron but it has come from the nucleus, not the outside of the atom.
Electrons are not normally expected to be found in the nucleus but neutrons can split into a positive proton (same mass but positive charge) and an electron (which has a negative charge to balance the positive charge) which is then ejected at high speed and carries away a lot of energy.
Beta decay causes the atomic number of the nucleus to increase by one and the mass number remains the same.
Positron (ß+) emission
If the nucleus has too few neutrons, a proton will turn into a neutron and emit a fast-moving positron. This positron can be called a beta plus (β+) particle - this process is known as positron emission. A positron is the antimatter version of an electron. It has the same relative mass of zero, so its mass number is zero, but a +1 relative charge. It can be written as 0+1e, however sometimes it is also written as 0+1β.
Beta plus decay - positron emission - causes the atomic number of the nucleus to decrease by one and the mass number remains the same.
A re-arrangement of the particles in a nucleus can move the nucleus to a lower energy state. The difference in energy is emitted as a very high frequency electromagnetic wave called a gamma ray. After emitting an alpha or beta particle, the nucleus will often still have excess energy and will again lose energy. A nuclear re-arrangement will emit the excess energy as a gamma ray.
Gamma ray emission causes no change in the number of particles in the nucleus meaning both the atomic number and mass number remain the same.
Neutron emission
Occasionally it is possible for a neutron to be emitted by radioactive decay. This can occur naturally, ie absorption of cosmic rays high up in the atmosphere can result in neutron emission, although this is rare at the Earth's surface. Or it can occur artificially, eg the work done by James Chadwick firing alpha particles at beryllium resulted in neutrons being emitted from that.
A further example of neutron emission is in nuclear fission reactions, where neutrons are released from the parent nucleus as it splits.
Neutron emission causes the mass number of the nucleus to decrease by one and the atomic number remains the same.
Properties of nuclear radiations
The different types of radiation are often compared in terms of their penetrating power, their ionising power and how far they can travel in the air.
Beta minus decay
If the nucleus has too many neutrons, a neutron will turn into a proton and emit a fast-moving electron. This electron is called a beta minus (β-) particle - this process is known as beta radiation. A beta particle has a relative mass of zero, so its mass number is zero. As the beta particle is an electron, it can be written as 0-1e. However, sometimes it is also written as 0-1β. The beta particle is an electron but it has come from the nucleus, not the outside of the atom.
Electrons are not normally expected to be found in the nucleus but neutrons can split into a positive proton (same mass but positive charge) and an electron (which has a negative charge to balance the positive charge) which is then ejected at high speed and carries away a lot of energy.
Beta decay causes the atomic number of the nucleus to increase by one and the mass number remains the same.
Positron (ß+) emission
If the nucleus has too few neutrons, a proton will turn into a neutron and emit a fast-moving positron. This positron can be called a beta plus (β+) particle - this process is known as positron emission. A positron is the antimatter version of an electron. It has the same relative mass of zero, so its mass number is zero, but a +1 relative charge. It can be written as 0+1e, however sometimes it is also written as 0+1β.
Beta plus decay - positron emission - causes the atomic number of the nucleus to decrease by one and the mass number remains the same.
A re-arrangement of the particles in a nucleus can move the nucleus to a lower energy state. The difference in energy is emitted as a very high frequency electromagnetic wave called a gamma ray. After emitting an alpha or beta particle, the nucleus will often still have excess energy and will again lose energy. A nuclear re-arrangement will emit the excess energy as a gamma ray.
Gamma ray emission causes no change in the number of particles in the nucleus meaning both the atomic number and mass number remain the same.
Neutron emission
Occasionally it is possible for a neutron to be emitted by radioactive decay. This can occur naturally, ie absorption of cosmic rays high up in the atmosphere can result in neutron emission, although this is rare at the Earth's surface. Or it can occur artificially, eg the work done by James Chadwick firing alpha particles at beryllium resulted in neutrons being emitted from that.
A further example of neutron emission is in nuclear fission reactions, where neutrons are released from the parent nucleus as it splits.
Neutron emission causes the mass number of the nucleus to decrease by one and the atomic number remains the same.
Properties of nuclear radiations
The different types of radiation are often compared in terms of their penetrating power, their ionising power and how far they can travel in the air.
All types of radioactive decay can be detected by photographic film, or a Geiger-Muller tube (G-M tube). The photographic film is chemically changed by the radiations so it can be developed to see if there has been exposure. In a G-M tube, the radiations ionise the gas inside and the resulting charged particles move across the chamber and get counted as charges rather like an ammeter.
Half-life
Radioactive decay is a random process. A block of radioactive material will contain many trillions of nuclei and not all nuclei are likely to decay at the same time so it is impossible to tell when a particular nucleus will decay.
It is not possible to say which particular nucleus will decay next but given that there are so many of them, it is possible to say that a certain number will decay in a certain time. Scientists cannot tell when a particular nucleus will decay but they can use statistical methods to tell when half the unstable nuclei in a sample will have decayed. This is called the half-life.
Half-life is the time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve or for the count rate to halve.
The Geiger-Muller tube is a device that detects radiation. It gives an electrical signal each time radiation is detected. These signals can be converted into clicking sounds, giving a count rate in clicks per second or per minute.
The activity of a radioactive substance is measured in Becquerel (Bq). One Becquerel is equal to one nuclear decay per second.
The illustration below shows how a radioactive sample is decaying over time:
Radioactive decay is a random process. A block of radioactive material will contain many trillions of nuclei and not all nuclei are likely to decay at the same time so it is impossible to tell when a particular nucleus will decay.
It is not possible to say which particular nucleus will decay next but given that there are so many of them, it is possible to say that a certain number will decay in a certain time. Scientists cannot tell when a particular nucleus will decay but they can use statistical methods to tell when half the unstable nuclei in a sample will have decayed. This is called the half-life.
Half-life is the time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve or for the count rate to halve.
The Geiger-Muller tube is a device that detects radiation. It gives an electrical signal each time radiation is detected. These signals can be converted into clicking sounds, giving a count rate in clicks per second or per minute.
The activity of a radioactive substance is measured in Becquerel (Bq). One Becquerel is equal to one nuclear decay per second.
The illustration below shows how a radioactive sample is decaying over time:
From the start of timing it takes two days for the activity to halve from 80 Bq down to 40 Bq. It takes another two days for the activity to halve again, this time from 40 Bq to 20 Bq. Note that this second two days does not see the activity drop to zero, only that it halves again. A third two-day period from four days to six days, sees the activity halving again from 20 Bq down to 10 Bq.
This process continues and although the activity might get very small, it does not drop to zero completely.The half-life of radioactive carbon-14 is 5,730 years. If a sample of a tree (for example) contains 64 grams (g) of radioactive carbon, after 5,730 years it will contain 32 g, after another 5,730 years that will have halved again to 16 g.
Calculating the isotope remaining
It should also be possible to state how much of a sample remains or what the activity or count should become after a given length of time. This could be stated as a fraction, decimal or ratio.
For example the amount of a sample remaining after four half-lives could be expressed as:
This could then be incorporated into other data. So if the half-life is two days, four half-lives is 8 days. Suppose a sample has a count rate of 3,200 Becquerel (Bq) at the start, then its count rate after 8 days would be 1/16th of 3,200 Bq = 200 Bq.
Example. The half-life of cobalt-60 is 5 years. If there are 100 g of cobalt-60 in a sample, how much will be left after 15 years?
15 years is three half-lives so the fraction remaining will be (½)3 = 1/8 = 12.5 g.
This process continues and although the activity might get very small, it does not drop to zero completely.The half-life of radioactive carbon-14 is 5,730 years. If a sample of a tree (for example) contains 64 grams (g) of radioactive carbon, after 5,730 years it will contain 32 g, after another 5,730 years that will have halved again to 16 g.
Calculating the isotope remaining
It should also be possible to state how much of a sample remains or what the activity or count should become after a given length of time. This could be stated as a fraction, decimal or ratio.
For example the amount of a sample remaining after four half-lives could be expressed as:
- a fraction - a ½ of a ½ of a ½ of a ½ remains which is ½ x ½ x ½ x ½ = 1/16 of the original sample
- a decimal - 1/16 = 0.0625 of the original sample
This could then be incorporated into other data. So if the half-life is two days, four half-lives is 8 days. Suppose a sample has a count rate of 3,200 Becquerel (Bq) at the start, then its count rate after 8 days would be 1/16th of 3,200 Bq = 200 Bq.
Example. The half-life of cobalt-60 is 5 years. If there are 100 g of cobalt-60 in a sample, how much will be left after 15 years?
15 years is three half-lives so the fraction remaining will be (½)3 = 1/8 = 12.5 g.
Nuclear equations
A nucleus changes into a new element by emitting nuclear radiations; these changes are described using nuclear equations.
Example
A nucleus changes into a new element by emitting nuclear radiations; these changes are described using nuclear equations.
Example