Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Marr College - Physics

National 4/5 Physics

Unit – Waves and Radiation

Key Areas

Page

• Sound 1

• Wave Parameters and Behaviours 9

• Light 21

• Electromagnetic Spectrum 34

• Nuclear Radiation 38

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Nat 4

Waves & Radiation

Key Area

Sound

Learning Intentions By the end of this key area I will be able to

Measuring the speed of sound, Nat 4

1. State which travels faster, light waves or sound waves.

2. Give examples of situations which demonstrate this differing

wave speed.

3. Describe a method of measuring the speed of sound using two

microphones.

4. Describe a method of measuring the speed of sound using the

difference in speed of light and speed of sound.

5. Solve problems involving the reflection of sound or sonar.

6. Explain why the speed of sound in solids is greater than the

speed of sound in gasses.

Analysis of sound waveforms, Nat 4

7. Draw the waveform produced by a sound wave on an

oscilloscope.

8. Explain the waveform on an oscilloscope in terms of loudness

and frequency changes in the sound signal.

9. Describe how a frequency meter could be used to measure the

frequency of a sound wave.

Ultrasound, Nat 4

10. State the range of frequencies which humans can hear.

11. State what is meant by ultrasound.

12. State the frequency, above which, sounds are known as

ultrasound.

13. Describe examples of the use of ultrasound in health care.

Measuring sound levels, Nat 4

14. State that sound level (loudness) is measured in decibels (dB)

using a sound level meter.

15. Describe a method of comparing the sound level in different

locations.

16. Explain why it is important for sound levels to be measured.

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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metre stick

Calculating the speed of sound in air experimentally using two microphones

Shown is an experimental setup with the equipment

that can be used to take measurements to allow the

speed of sound to be calculated.

Notice, the speed of sound is not measured. The

speed of sound in air is calculated.

Measure

• The distance between the two microphones

with a metre stick

• The time it takes the sound to travel from

microphone 1 to microphone 2 with timer.

Calculations

𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑠𝑜𝑢𝑛𝑑 = 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑚𝑖𝑐𝑟𝑜𝑝ℎ𝑜𝑛𝑒𝑠

𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 𝑓𝑜𝑟 𝑠𝑜𝑢𝑛𝑑 𝑡𝑜 𝑡𝑟𝑎𝑣𝑒𝑙 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑚𝑖𝑐𝑟𝑜𝑝ℎ𝑜𝑛𝑒𝑠

d = 1.00 m 𝑣 = 𝑑

𝑡

𝑡 = 0.00296 s =1.00

0.00296

v = ? 𝑣 = 338 m s−1 watch rounding

Calculating the speed of sound experimentally using the time delay between seeing and hearing an event

The equipment shown allows the speed of sound

to be calculated.

Method

• Pupil A hits the two pieces of wood

together.

• Pupil B sees the wood being hit starts

their stopwatch

• A short time later, pupil B hears the wood

hitting together stops their stopwatch.

Measure

• The distance between pupil A and pupil B with a trundle wheel or tape measure.

• The time between seeing the wood hitting together and hearing the wood being hit, with a stopwatch.

Timer

0.00296 S

microphone 1

start timer

microphone 2

stop timer

Labelled diagram

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Calculations

𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑠𝑜𝑢𝑛𝑑 = 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑝𝑢𝑝𝑖𝑙𝑠

𝑡𝑖𝑚𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑠𝑒𝑒𝑖𝑛𝑔 𝑎𝑛𝑑 ℎ𝑒𝑎𝑟𝑖𝑛𝑔 𝑤𝑜𝑜𝑑 𝑏𝑒𝑖𝑛𝑔 ℎ𝑖𝑡

Notes on this method

• This method works because the speed of light is very much faster than the speed of sound.

• The distance between the pupils must be large, more than 100 m, otherwise the time interval is too short to

measure.

• Due to human reaction time this method gives an unreliable value of the speed of sound.

Speed of light and the speed of sound

The speed of light is 300, 000, 000 m s-1, 3 x 108 m s-1.

The speed of sound is about 340 m s-1.

The speed of light is very much greater. There are many examples of us seeing events before hearing them.

Thunder and lightning

These are produced together but because light wave travels

faster than sound waves we see the flash before we hear the

thunder.

Fireworks

When a rocket explodes in the sky we see the flash then hear

the bang.

How far away is the rocket?

• Measure the time between seeing the flash and

hearing the bang, t.

• The speed of sound is 340 m s -1, v.

Calculation

• distance to rocket = v x t.

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Example on speed of sound in air by the clap echo method

A pupil stands 200 m from a large wall.

They clap their hands and1.20 seconds later they hear an echo

of their clap.

Calculate the speed of sound in air that this data gives.

Solution

d= 200 m but sound travels to wall and back so

d= 400 m 𝑣 =𝑑

𝑡

t = 1.20 ms-1 =400

1.20

v = ? = 333 m s-1

Speed of sound in different materials

The table opposite shows the speed of sound in different

materials.

The speed of sound in a gas is less than the speed in a liquid.

The speed in a liquid is less than in a solid.

Material

Speed of sound

m s-1

Air 340

Water 1480

Aluminium 6300

This difference in speed is because sound is a longitudinal wave and it travels by the particles in the material

vibrating into each other.

200 m

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Gas Liquid Solid

In a gas the particles are far apart so it

takes more time for the vibrations to pass

through the gas.

In a liquid the particles are much

closer together so it takes less

time for the vibrations to pass

hrough the liquid.

In a solid the particles are very

close together so it takes even less

time for the vibrations to pass

through the solid.

Sound does not travel through a vacuum

A vacuum has no particles. In a vacuum there is no solid, liquid or gas.

Space is the best example of a vacuum.

Sound cannot pass through a vacuum since there are no particles to vibrate.

Sound through water

Sound travels through water without much loss of energy. This is why many animals including whales and dolphins

communicate by sound. These sounds can travel many miles.

Ships use a system called SONAR (SOund Navigation And Ranging) to check the depth of the water, to detect fish

or to detect submarines under the water.

In this system a pulse of sound is transmitted (sent out) and an echo is received (detected).

From this the depth of the water can be found.

Example on SONAR

A ship sends a pulse of sound down towards some fish. An

echo is received 1.80 seconds later.

The speed of sound in water is 1, 480 m s-1.

Calculate the distance to the fish.

Solution

t = 1.80 s 𝑑 = 𝑣 ×𝑡

v = 1, 480 ms-1 = 1, 480 ×1.80

d = ? = 2, 664 m

However, this is the distance down to the fish and back up

so the distance to the fish is 1, 332 m.

d = 1, 330 m (round to 3 sig figs)

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Sound waves on the oscilloscope

Sound is a wave which is produced by vibrations. A sound wave can be picked up using a microphone, and the

electrical signal can be analysed using an oscilloscope.

If the frequency of the sound is increased this means that more waves are produced each second. The pitch of the

note gets higher and more waves will be shown on the oscilloscope screen.

If the volume of the sound is increased, the amplitude of the signal on the screen increases as the sound has more

energy.

Example

A microphone is connected to an oscilloscope.

The microphone detects the sound produced by a

loudspeaker.

Shown below is the trace produced on the oscilloscope.

A louder sound of half the frequency is now detected

by the microphone.

Draw the trace produce on the oscilloscope.

The controls of the oscilloscope remain unaltered. Solution Louder sound larger amplitude (taller) Half frequency half number of waves

Original signal

Same frequency, louder

Lower frequency, same volume

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Measuring the frequency of sound

Method 1: using a frequency meter

Shown below is a signal generator connected to a loudspeaker and a frequency meter.

When the signal generator is switched on the loudspeaker vibrates to produce sound.

Energy change

Electrical energy Sound energy

The frequency meter measures and displays the frequency of the electrical signal.

Method 2: using a an oscilloscope or computer display

A signal generator or microphone could be connected to an

oscilloscope or a computer.

The trace that would be displayed would be similar to that

shown below.

Measurements needed

• Number of waves, n

• Time to make these waves, t

Calculation

• 𝑓 =𝑁

𝑡

The time between the two lines = 0.015 s

The number of waves between the two lines = 6

Calculate the frequency of the wave pattern.

Solution

t = 0.015 s 𝑓 =𝑁

𝑡

N = 6 =6

0.015

Loudspeaker

Signal generator

Frequency meter

480 Hz

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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f = ? = 400 Hz

Ultrasound

Humans can only hear between about 20 Hz and 20, 000 Hz.

Frequencies above 20, 000 Hz are known as ultrasound.

There are many uses of ultrasound. One very common use is scanning pregnant women to monitor the development

of their unborn baby.

A pulse of ultrasound is transmitted into the mother and the time for the reflected pulse to be received is measured.

A computer then uses this information to build up an image of the unborn baby.

Example

A pulse of ultrasound is transmitted from the transducer into a

mother body and the reflected pulse is detected after a time of

0.16 milliseconds.

The speed of ultrasound in human tissue

is 1, 500 m s-1.

Calculate the distance from the transducer to the unborn baby

Solution

t = 0.16 milliseconds, convert to seconds

divide by 1000

t = 0.00016 𝑑 = 𝑣 ×𝑡

v = 1, 500 m s-1 = 1, 500 ×0.00016

d = ? = 0.24 m

However, this is the distance down to the unborn baby and

back to the transducer so the distance to the unborn baby is

0.12 m.

Sound level (loudness)

The loudness of a sound is called the sound level and is measured in

decibels, dB.

Sound levels above a safe level can permanently damage hearing.

By measuring sound levels in the workplace employees will know

when they need to wear ear protection.

Measurement of sound level

Sound level can be measured using a sound level meter.

In order to obtain a reliable measurement of the sound level, several

meter readings would be taken and an average value calculated.

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Nat 5

Waves & Radiation

Key Area

Wave parameters & behaviours

Learning Intentions By the end of this key area I will be able to

Wave patterns

1. State that all waves carry energy.

2. State the meaning and unit of frequency.

3. State the meaning and unit of wavelength.

4. Draw a transverse waveform.

5. On a transverse waveform draw the direction of the travel of the

wave and the direction of particle vibration.

6. On a transverse waveform identify the crest and the trough.

7. Give examples of transverse waves.

8. Using data on a transverse waveform calculate:

amplitude number of waves

wavelength frequency

9. State that the amplitude of a wave is a measure of the energy of

the wave.

10. Carryout calculations involving number of waves, time and

frequency.

11. Carryout calculations involving number of waves, distance and

wavelength.

12. Carryout calculations involving distance, speed and time.

13. Carryout calculations involving frequency, wavelength and

speed.

14. Draw a longitudinal waveform.

15. On a longitudinal waveform draw the direction of the travel of

the wave and the direction of particle vibration.

16. On a longitudinal waveform identify a compression and a

rarefaction.

17. Give examples of longitudinal waves.

18. Using data on a longitudinal waveform calculate:

amplitude number of waves

wavelength frequency

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Reflection

19. State that when a wave reflects there is no change in wavelength,

frequency or speed.

Refraction

20. Refraction occurs when waves pass from one medium to

another.

21. Identify the normal, angle of incidence and angle of refraction in

ray diagrams showing refraction.

22. State that when a wave refracts there is a change in both

wavelength and speed of the wave.

23. State that when a wave refracts there is no change in frequency

of the wave.

Diffraction

24. State that diffraction is the curving of a wave as it passes around

an object, the end of a barrier or as the wave passes through a

gap or slit.

25. Draw wave diagrams to show the diffraction of a wave as it

passes a barrier or around an object.

26. Draw wave diagrams to show the diffraction of a wave as it

passes through a gap or slit.

27. State that waves of long wavelength will diffract more than

waves of short wavelength.

28. Draw wave diagrams to show how the amount of diffraction

changes with wavelength.

29. State that wave will diffract more when passing through a

narrow slit than through a wide slit.

30. Draw wave diagrams to show how the amount of diffraction

changes with the width of the slit.

31. State that when a wave diffracts there is no change in

wavelength, frequency or speed.

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Waves carry energy

All waves move from a transmitter to a receiver.

A lamp transmits (sends out) a light wave and it is received (picked up) by your eye.

A mobile phone transmitter sends out a microwave and your mobile phone receives the wave.

When you speak you transmit a sound wave and the ear of the listener receives it.

All waves or “signals” carry or transfer energy.

In order for the wave to travel there must be some vibration.

Transverse wave patterns

The diagram below shows a transverse wave pattern.

In all transverse waves the vibration of the wave is always at right angles to the direction in which the wave is moving.

Radio waves travel from transmitter to receiver

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Key terms for a transverse wave

The diagram below shows a transverse wave with several key terms labelled

Crest: the highest point on the wave

Trough: the lowest point on the wave

Amplitude: the distance from the middle of the wave to the top (crest) or from the middle of the wave to the

bottom (trough).

The amplitude is a measure of the energy of a wave. The larger the amplitude of the wave then the greater

will be the energy being carried by the wave.

Wavelength: the length of one wave. This is the distance from one point to the next identical point on the

wave. In this diagram it is the distance from one trough to the next trough.

Wavelength is measured in metres (m) and has the symbol (lambda).

Wave speed: the speed at which the wave travels.

The wave speed is measured in metres per second (m s-1) and has the symbol v.

Frequency: the number of waves per second.

Frequency is measured in hertz (Hz) and has the symbol f.

Period: the time for one wave.

Period is measured in seconds (s) and has the symbol T.

Key equations

𝑝𝑒𝑟𝑖𝑜𝑑 = 1

𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦

𝑇 = 1

𝑓

𝑤𝑎𝑣𝑒 𝑠𝑝𝑒𝑒𝑑 = 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑟𝑎𝑣𝑒𝑙𝑙𝑒𝑑

𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 𝑣 =

𝑑

𝑡

d

v t

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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𝑤𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡ℎ = 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑓 𝑤𝑎𝑣𝑒𝑠

𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑤𝑎𝑣𝑒𝑠

Not on the equations list but worth learning.

= 𝑑

𝑛

d

n

𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑤𝑎𝑣𝑒𝑠

𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛

𝑓 = 𝑁

𝑡

N f t

Example 1

The transverse wave shown was

produced in 0.5 seconds

a) State the amplitude.

b) State the number of waves.

c) Calculate the frequency of the wave.

d) Calculate the period of a wave.

Solution

a) Amplitude = height from middle of wave to top = 1.2 / 2 = 0.6 m

b) Number of waves = 3.5 waves

c) N = 3.5 𝑓 = 𝑁

𝑡

t= 0.5

𝑓= ? 𝑓 = 3.5

0.5 => 𝑓 = 7 Hz

d) f = 7 Hz 𝑇 = 1

𝑓

T = ?

𝑇 = 1

7 => 𝑇 = 0.14 s

1.2 m

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Example 2

Shown opposite is a transverse wave.

a) State the amplitude of this wave.

b) State the number of waves in this transverse wave.

c) Calculate the wavelength of this wave.

Solution

a) Amplitude = height of wave from middle = 2 m

b) Number of waves = 3

c) d = 18 m =

𝑑

𝑛

n = 3

= ? = 18

3 => = 6 m

Example 3

Shown opposite is the circular wave pattern produced when a

stone lands in the water.

Each solid line represents a crest and each dotted line represents

a trough.

The distance from the centre of the wave pattern to the outer

edge is 6 m.

The speed of the water wave is known to be 4.0 m s-1.

a) Calculate the time it took to produce this pattern.

b) State the number of waves shown in this pattern.

c) Calculate the wavelength of the water wave.

Solution

a) d = 6 m 𝑑 = 𝑣 ×𝑡

v = 4.0 m s-1 6 = 4 ×𝑡

𝑡= ?

𝑡 = 6

4 => 𝑡 = 1.5 s

b) Number of waves = 3

c) d = 6 m =

𝑑

𝑛

n = 3

= ? = 6

3 => = 2 m

6 m

0 m

18 m

2 m

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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The wave equation

For light waves, sound waves and water waves travelling along river or over the surface of the sea, the wave

speed, frequency and wavelength are linked by the following equation.

Wave speed (m s-1) = frequency (Hz) x wavelength (m)

𝑣 = 𝑓 ×

Get the units correct

Time is always measured in seconds. To convert from minutes to seconds, multiply by 60.

t = 5 minutes = 300 seconds

frequency is always measured in Hz. To convert from kHz (kilohertz) to Hz, multiply by 1 000.

f = 7 kHz = 7 000 Hz

wavelength is always measured in metres. To convert from mm (millimetres) to m, divide by 1 000.

= 600 mm = 0.6 m

Example 4

A wave of frequency 5 Hz has a wavelength of 4 m. Calculate the speed of the wave.

Solution

f = 5 Hz 𝑣 = 𝑓 ×

= 4 m = 5×4

v = ? 𝑣 = 20 m s−1

Example 5

A wave of frequency 50 Hz moves at a speed of 400 m s-1. Calculate the wavelength of the wave.

Solution

f = 50 Hz 𝑣 = 𝑓 ×

v = 400 m s−1 400 = 50 ×

= ? =400

50

= 8 m

Example 6

A wave of frequency 4 kHz has a wavelength of 50 mm.

Calculate the speed of the waves.

Solution

f = 4 kHz = 4 000 Hz 𝑣 = 𝑓 ×

=50 mm = 0.05 m 𝑣 = 4 000 ×0.05

v = ? v = 200 m s-1

v

f

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Longitudinal wave patterns

The diagram below shows a longitudinal wave pattern.

In a longitudinal wave the particles vibrate parallel to the direction of the wave.

Compression: where the particles are close together

Rarefaction: where the particles are spread out.

How longitudinal waves move through materials

Longitudinal waves can only pass through solids, liquids and gasses.

When the particles vibrate they hit into each other so the wave and energy is passed through the material.

Longitudinal waves cannot pass through a vacuum because there are no particles in a vacuum.

Since there are no particles to compress against each other there can be no longitudinal wave.

Examples of longitudinal waves

The most common longitudinal wave is sound.

Other examples include ultrasound used for scanning pregnant ladies and waves in a spring.

P-waves produced during an earthquake.

Direction of vibration

Direction of wave

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Example 1

Shown below is a longitudinal wave.

The wave is travelling at 72 m s-1.

a) Which labels represent compressions?

b) Which labels represent rarefactions?

c) Calculate the wavelength of the wave.

d) Calculate the frequency of the wave

e) State what this frequency means.

Solution

a) B and D are compressions

b) A and C are rarefactions

c) d = 12 m =

𝑑

𝑛

n = 1.5

= ? = 12

1.5 => = 8 m

d) = 8 m 𝑣 = 𝑓 ×

v = 72 m s−1 72 = 𝑓 × 8

𝑓 = ? 𝑓 =72

8

𝑓 = 9 Hz

e) A frequency of 9 Hz means that there are 9 waves made every second.

A B C D

12 m

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Reflection: What happens to velocity, wavelength and frequency during reflection?

The answer is, none of these change during reflection.

During reflection

• velocity does not change

• wavelength does not change

• frequency does not change

• The only thing that changes is the direction and it

can be predicted by the Law of Reflection.

Refraction: What happens to velocity, wavelength and frequency during refraction?

The answer is, both velocity and wavelength change

during refraction.

Frequency is the odd one out, it does not change. It

remains constant.

During refraction

• velocity changes

• wavelength changes

• frequency does not change

The diagram above shows light travels from air into glass. The light refracts because it slows down and the

wavelength gets smaller.

Waves in water refract when the move from deep

water to shallow water.

The waves slow down and the wavelength decreases.

This can cause the direction of the waves to change.

The frequency does not change.

What is diffraction?

Diffraction occurs when a wave passes an edge, passes through a narrow gap or goes past an object.

None of the properties of a wave are changed by diffraction. The wavelength, frequency, period and speed

are the same before and after diffraction. The only change is the direction in which the wave is travelling.

Incident

wave

Reflected

wave

air glass

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Diffraction and gap size

As the gap gets smaller the diffraction effect increases. This means that there is more spreading or curving

of the wave as the gap gets smaller.

When a wave passes through a gap the diffraction effect is greatest when the width of the gap is about the

same size as the wavelength of the wave. Diffraction past a barrier or object Diffraction through a wide gap Diffraction through a narrow gap

Diffraction and wavelength

Longer wavelengths diffract more than short wavelengths.

The diagrams below show a short wavelength and a long wavelength diffracting through the same width of

gap.

Short wavelength

Only a little diffraction

Long wavelength

More diffraction

Water waves and diffraction

When water waves move through a gap in a seawall

the plane or straight waves become curved.

The diagram opposite shows the plane wave being

curved as it passes through the gap.

plane wave

curved

wave

waves diffract around edge

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Radio waves and diffraction over a hill

Radio waves cannot pass though hills but can

diffract round a hill.

Since longer wavelengths diffract more than short

wavelengths a house behind a hill is more likely to

receive long wavelength radio waves than short

wavelength radio waves.

Radio waves and diffraction around the Earth

The same is true for radio waves diffracting around

the Earth.

The ground wave is a wave of long wavelength, so it

can diffract around the Earth.

The sky wave is of a shorter wavelength so it does

not diffract as much and therefore moves into the

upper atmosphere where it may reflect and come

back to Earth.

sky wave has short

upper atmosphere

ground wave has long

Earth is curved

Marr College Physics Department National 4/5 Summary Notes Waves and Radiation Unit

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Nat 5 Waves & Radiation

Key Area Light

Learning Intentions By the end of this key area I will be able to

Reflection

17. State the law of reflection.

18. Draw a normal line.

19. Measure angles of incidence and reflection.

20. Draw a ray diagram to show reflection from a plane mirror.

21. Draw a ray diagram to show reflection from a concave mirror.

22. Draw a ray diagram to show reflection from a convex mirror.

23. Identify the focal point of a concave reflector.

24. Explain why maximum energy is detected at the focal point.

25. Describe examples of the use of concave reflectors.

Refraction

26. Describe when refraction of light happens.

27. State that refraction is caused by a change of speed when waves

pass from one medium to another.

28. State the speed of light in air.

29. State that the speed of light in glass and water is less than the

speed of light in air.

30. Draw ray diagrams to show the refraction of light as it passes

from air to glass and glass to air.

31. Identify and measure angles of incidence, reflection and

refraction.

32. Draw a ray diagram to show the path monochromatic light takes

as it passes through a glass prism.

33. Draw a ray diagram to show the path white light takes as it

passes through a glass prism and forms a visible spectrum.

34. State that white light is a mixture of all the colours in the visible

spectrum.

35. Explain, in terms of speed, why a visible spectrum is produced

by white light passing through a prism.

36. Draw a convex or converging lens.

37. Draw a ray diagram to show the path of light as it travels

through a convex or converging lens.

38. Identify the focal point of a convex or converging lens.

39. Describe examples of the use of a convex or converging lens.

For example: the eye or a camera.

40. Draw a concave or diverging lens.

41. Draw a ray diagram to show the path of light as it travels

through a concave or diverging lens.

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Law of Reflection

The angle of incidence equals the angle of reflection.

The diagram below shows this.

The normal line

The normal line is at right angles, 90°, to the mirror at the point where the light meets the

mirror.

Angles are always measured from the normal line, not from the mirror.

Example

The diagram below shows the path light takes when it reflects from a plan mirror.

Four angles have been marked on the diagram.

a) State the angle of incidence.

b) State the angle of reflection.

Normal line

48° 48°

42° 42°

Normal line

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Solution

a) The angle of incidence is 48°.

b) The angle of reflection is 48°.

Reflection from curved mirrors and reflectors

Concave reflectors

Concave mirrors and reflectors are used to reflect waves to a single point called the focal

point. The focal point is shown in the diagram below by the letter F.

The incoming rays reflect to point F, the focal point.

This means that many waves will meet at one point.

If a detector or aerial is placed at the focal

point then maximum energy is detected.

This arrangement is used in satellite dish

receivers.

Rays reflect to

focal point.

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Convex reflectors

Convex reflectors or mirrors are used to

reflect light so that it spreads out.

These convex mirrors are often placed at

corners in shops and stairways to allow

people to “see round the corner”.

Refraction of light

Refraction occurs when waves pass from one medium (air, glass, water) to another. The

waves change speed when they change medium. This often causes them to change direction.

The angle between the incident ray and the normal is called the angle of incidence.

The angle between the refracted ray and the normal is called the angle of refraction.

The normal is the line at 90° to the boundary at the point where the wave hits the boundary.

Key points.

• When the light travels from air into glass it refracts towards the normal line.

• When the light travels from glass into air it refracts away from the normal line.

• In this diagram, the ray entering the glass block and the ray leaving the glass block are

parallel. This is because the sides of the glass block are parallel.

Angle of refraction

Angle of incidence

Normal

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What causes the change in direction?

Whenever the wave moves from air into another medium (glass, water) it will slow down.

When the wave slows down, it refracts towards the normal.

When the wave moves from glass back into the air it will speed up.

When it speeds up it refracts away from the normal.

What is the speed of light in air?

The speed of light in air or a vacuum is 300, 000, 000 m s-1, also written as 3.0 x 108 m s-1.

When light moves from air into glass, water or any other medium it will slow down.

Light never travels faster than 300, 000, 000 m s-1.

This is the fastest speed possible, eight times round the Earth in one second.

Nothing can travel faster than the speed of light.

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Refraction by a prism

Shown opposite is the path taken by a beam

of red light when it passes through a glass

prism.

Key points.

• When the light travels from air into

glass it refracts towards the normal

line.

• When the light travels from glass into

air it refracts away from the normal

line.

Since it is red light going in, then only red

light will come out.

Shown opposite is the path taken by a beam of

white light when it passes through a glass

prism.

Key points.

• When the light travels from air into

glass it refracts towards the normal line.

• When the light travels from glass into

air it refracts away from the normal

line.

• A visible spectrum is produced.

• This is because white light is made up

of all the colours in the visible

spectrum.

• The red light refracts less than the

violet light so the colours are split.

• The red light slows a little so it refracts

only a little.

• The violet light slows even more so it

refracts more than the red light and they

follow different paths.

• When the light leaves the glass it once

again travels at 300, 000, 000 m s-1.

Excellent simulation

http://www.quora.com/How-do-prisms-separate-

white-light-into-different-colored-light

You are expected to be able to draw both of these diagrams and show that the red light refracts less

than the violet light.

red light

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A rainbow is produced by white light refracting through a raindrop, not a glass prism.

Light moving between air and water

When light moves from air into water it slows

down.

The diagram opposite shows the path light would

take as it moves from water into air.

When light moves from water into air it speeds

up.

This means that the light will refract away from

the normal.

Viewing an object under the water

Light comes from the object under the water out

into the air.

The solid lines in the diagram opposite show the

actual path of the light. The light refracts as it

moves from the water into the air.

Water always turns out to be deeper than it looks,

and glass is always thicker than it looks. This is

due to refraction.

The light ray changes direction at the surface.

The brain assumes that it has travelled in a

straight line and so has come from a point

directly above the true position.

Observer’s

eye

Normal

line

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Convex or converging Lenses

Convex lenses are thicker in the middle than at

the edges.

Convex lenses make the rays converge. The

thicker the lens the more refraction it causes.

The diagram opposite shows the normal lines and

the path of rays passing through the lens.

You will never be asked to draw normal lines on

a curved surface.

The diagrams opposite show a thin convex lens

and a fatter convex lens.

Both bring the light to a focus.

The point of focus is called the focal point.

The more curved (fatter) the lens the closer the

focal point is to the lens.

The distance from the middle of the lens to the

focal point is called the focal length.

Convex lenses have many uses.

• To make an image on the retina of the eye.

• To make an image on the screen of a camera

• To make a sharp image on the screen used by a multimedia projector.

• In telescopes and binoculars to magnify distant objects.

Concave or diverging lens

Concave lenses are thinner at the middle than at

the edges. Concave lenses make rays of light

diverge. The light spreads out.

• Some glasses have a concave lens.

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• Peepholes in doors use concave lenses.

Hint: How to remember which shape is concave and which shape is convex

Concave lenses cave in to the middle of the lens. They are hollow towards the middle.

If you remember this then it’s easy to remember the fat one is convex.

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Electromagnetic spectrum

Nat 5 Waves & Radiation Key Area

Electromangetic Spectrum Learning Intentions

By the end of this key area I will be able to

1. State the relative frequency and wavelength of bands of the electromagnetic spectrum.

2. All bands in the electromagnetic spectrum are transverse waves.

3. Describe some sources for each band of the electromagnetic spectrum.

4. Describe some detectors used for each band of the electromagnetic spectrum.

5. Describe some applications of bands of the electromagnetic spectrum.

6. Describe the relationship between frequency and energy associated with a particular band of electromagnetic radiation.

7. State that all members of the electromagnetic spectrum travel at the speed of light and that this speed is

3x108 ms-1 in vacuum.

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About the Electromagnetic Spectrum

• The electromagnetic spectrum is a family of radiation waves.

• All members travel as transverse waves.

• All members transfer energy.

• All members travel at a speed of 3x108 ms-1 through vacuum and through air.

~ 10-12 ~ 10-10 ~ 10-8 ~ 10-7 ~ 10-5 ~ 10-2 ~ 103

Gamma rays X-rays Ultraviolet Visible light Infrared Microwaves Radio + TV

~ 1020 ~ 1018 ~ 1016 ~ 1015-14 ~ 1012 ~ 108 ~ 104

Sources of electromagnetic radiation

(There are many other sources of electromagnetic radiation that you may know from

previous/current studies, these are just examples).

Gamma rays - Solar flare, particle accelerators

X-rays - X-ray tube, particle accelerators, neutron stars

UV - The Sun, UV lamps

Visible - Tungsten filament lamp, LEDs, candles, torches

Infrared - Electric heater, coal fire, the Sun, TV remote, Human body

Microwaves - Magnetron (in microwave ovens), masers, Cosmic Microwave Background

Radio + TV - RF transmitter, stars

increasing wavelength (m)

increasing frequency (Hz)

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Applications of electromagnetic radiation

(There are many other applications of electromagnetic radiation that you may know from

previous/current studies, these are just examples).

Gamma rays - used to treat cancer (radiotherapy)

X-rays - used to detect breaks and fractures in bones

UV - used to treat skin conditions such as acne

Visible - allows us to see

Infrared - used to treat injured muscle tissue

Microwaves - heats food quickly, used to transmit and receive mobile phone signals

Radio + TV - transmit and receive information (without the need for wires)

Detectors of electromagnetic radiation

(There are many other detectors of electromagnetic radiation that you may know from

previous/current studies, these are just examples).

Gamma rays - Geiger-Mϋller tube

X-rays - Photographic film

UV - Fluorescent paint, UV photographic film

Visible - Photodiode, photographic film

Infrared - Blackened thermometer, IR camera, IR photographic film

Microwaves - Diode probe

Radio + TV - Aerial

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Frequency and Energy

• The higher the frequency of electromagnetic radiation, the greater the energy transferred.

o For example, gamma rays carry more energy than radio waves.

• This relationship influences the applications for particular radiations.

o For example, radio waves cannot be used to obtain images of bone structure

because they do not have enough energy to pass through human tissue.

o Higher energy X-rays are required for this application.

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Nuclear radiation

Nat 5 Waves & Radiation Key Area

Nuclear Radiation Learning Intentions

By the end of this key area I will be able to

1. State what is meant by an alpha particle, beta particle and gamma ray.

2. State that radiation energy may be absorbed in the medium through which it passes.

3. State the approximate range through air, and absorption of alpha, beta and gamma radiation.

4. State what is meant by the term ionisation.

5. State the relative ionising effects of different types of radiation.

6. State that radiation can kill living cells or change the nature of living cells.

7. Describe one medical use of radiation based on the fact that radiation can destroy cells.

8. Describe one use of radiation based on the fact that radiation is easy to detect.

9. Describe factors affecting the background radiation level.

10. State that the activity of a radioactive source is the number of decays per second and is measured in becquerels (Bq), where one becquerel is one decay per second.

11. Carry out calculations involving the relationship between activity, number of decays and time.

A = N / t

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12. State that the absorbed dose is the energy

absorbed per unit mass of the absorbing material.

D = E / m

13. State that the gray (Gy) is the unit of absorbed dose and that one gray is one joule per kilogram.

12. Carry out calculations using the relationship between absorbed dose, energy and mass.

13. State that a radiation weighting factor is given to each kind of radiation as a measure of its biological effect.

14. State that the equivalent dose is the product of absorbed dose and radiation weighting factor and is measured in

sieverts (Sv). H = DWr

15. Carry out calculations involving the relationship between equivalent dose, absorbed dose and radiation weighting factors.

16. State that the risk of biological harm from an exposure to radiation depends on the:

a) absorbed dose b) type of radiation, e.g. α, β, γ, slow neutron c) body organs or tissue exposed

17. Compare equivalent dose due to a variety of natural and artificial sources.

18. State that the equivalent dose rate is the equivalent dose per unit time.

Ḣ = H / t

19. Carry out calculations involving the relationship between equivalent dose rate, equivalent dose and time.

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20. State that the average annual background radiation in the UK is 2.2 mSv.

21. State that the annual effective dose limit for a member of the public is 1 mSv.

22. State that the annual effective dose limit for a radiation worker is 20 mSv.

23. Describe the principles of a method for measuring background radiation.

24. State examples of sources of background radiation.

25. State that the activity of a radioactive source decreases with time.

26. State the meaning of the term ‘half-life’.

27. Describe the principles of a method for measuring the half-life of a radioactive source.

28. Determine the half-life of a radioactive isotope from graphical or numerical data.

29. Carry out calculations to determine the activity of a source after a particular time, given the half-life of the source.

30. Describe applications of nuclear radiation in medicine and industry.

31. Describe, in simple terms, a fission reaction.

32. Explain in simple terms a chain reaction.

33. State the advantages and disadvantages of using nuclear power for the generation of electrical energy.

34. Describe the problems associated with the disposal and storage of radioactive waste.

35. Describe, in simple terms, a fusion reaction.

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36. Explain the possible advantages of

generating electrical energy using a fusion reactor.

37. Describe some practical difficulties associated with fusion reactions including plasma containment.

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Atoms

• Every substance is made up of atoms. Each element is made up of the one kind of atom. Sometimes these atoms are combined together to form molecules. Inside each atom there is a central part called the nucleus. The nucleus contains two particles:

protons: these have a positive charge neutrons: these have no charge.

• Surrounding the nucleus are negatively charged electrons.

• An uncharged atom will have the same number of protons and electrons.

• Consider the element helium, which has two neutrons and two protons in the nucleus, and two electrons surrounding the nucleus. This can be represented as:

Ionisation

• Atoms are electrically neutral because they have an equal balance of protons (+) and electrons (-)

• It is possible to add electrons or remove electrons

• When an electron is added to an atom a negative ion is formed.

• When an electron is removed a positive ion is formed.

• The addition or removal of an electron or electrons is called ionisation. (It is important to remember that the nucleus remains unchanged)

Ionising Radiations

• There are some atoms which have unstable nuclei.

• Unstable nuclei emit particles and excess energy (electromagnetic radiation) in order to make the nucleus more stable.

• These atoms are called radioactive.

• The particles and electromagnetic radiation emitted can cause ionisation and so are known as ionising radiations.

Nucleus containing protons

and neutrons

Electrons orbit the nucleus

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There are three types of ionising radiation: Alpha particles are the nuclei of helium atoms. They have 2 neutrons and 2 protons in the nucleus and are therefore positively charged. Beta particles are fast moving electrons. They are special electrons because they come from within the nucleus of an atom. They are caused by the breakup of a neutron into a positively charged proton and a negatively charged electron. Gamma rays are caused by energy changes in the nuclei. Often the gamma rays are sent out at the same time as alpha or beta particles. Gamma rays have no mass or charge and carry energy from the nucleus leaving the nucleus in a more stable state. Properties of radiation Alpha particles will travel about 5 cm through the air before they are fully absorbed. They will be stopped by a sheet of paper. Alpha particles produce much greater ionisation density than beta particles or gamma rays. They move much more slowly than beta or gamma radiation. Beta particles can travel several metres through air and will be stopped by a sheet of aluminium a few millimetres thick. They have a lower ionisation density than alpha particles. Gamma rays can only be stopped by a very thick piece of lead. They travel at the speed of light and have a very low ionisation density. Detection of Radiation A Geiger-Müller (GM) tube is used to detect alpha, beta and gamma radiation. If any of these enter the tube, ions are produced resulting in a small current flow. The current is amplified and a counter counts the number of events giving an indication of the level of radioactivity.

Effects of radiation on living things All living things are made of cells. Ionising radiation can kill or change the nature of healthy cells. This can lead to different types of cancer. Due to the danger of ionising radiation there is a need to measure the exposure to make sure that people are safe.

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Uses of the properties of radiation (Based on radiation killing cells) Radiation can be used in the treatment of cancer. The radioactive source, cobalt-60 kills malignant cancer cells. The source is rotated around the body centred on the cancerous tissue so the cancerous cells receive radiation all the time. However, as the source is moving the healthy tissue only receives the radiation for a short time and is therefore not damaged. Radiation can be used to sterilise medical instruments. This allows the instruments to be packaged first and then irradiated through the packing to destroy any bacteria. The instruments will then remain sterile until they are ready for use. (Based on detecting radiation) Radioactive tracers help doctors to examine the insides of our bodies. Iodine-131 is used to see if our thyroid glands are working properly. The thyroid gland controls the rate at which our body functions. The thyroid gland absorbs iodine, so a dose of radioactive iodine (the tracer) is given to the patient. Doctors can then detect the radioactivity of the patient’s throat, to see how well the patient’s thyroid is working. (Industrial uses) Radiation is used in industry in detectors that monitor and control the thickness of materials such as paper, plastic and aluminium. The thicker the material, the more radiation is absorbed and the less radiation reaches the detector. It then sends signals to the equipment that adjusts the thickness of the material.

Dosimetry

Dosimetry involves measuring and calculating radiation dose in matter and tissue. This enables us to make predictions of the effect of radiation on living tissue and therefore put protective measures in place.

Activity The activity, A, of a radioactive source is the number of decays, N, per second. Activity is measured in becquerels where 1 Bq = 1 decay per second.

number of decays

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𝐴 =𝑁

𝑡

Example A sample of radioactive material undergoes 3.6x106 decays in 1 hour. Calculate the activity of the source. A = ? N = 3.6x106

t = 1 hour = 3600 s

𝐴 =𝑁

𝑡

=3.6×106

3600

= 1000 𝐵𝑞

Absorbed dose Increasing the transfer of radiation energy to the body increases the chance of damage to the body. The absorbed dose, D, is the energy absorbed per unit mass of the absorbing material and is measured in Grays, Gy.

𝐷 =𝐸

𝑚

1 Gy = 1 J/kg

Example A sample of lung tissue of mass 80 g absorbs 400 µJ of energy from gamma rays. Calculate the absorbed dose. D = ? E = 400 µJ = 4x10-4 J m = 80 g = 0.08 kg

𝐷 =𝐸

𝑚

Activity (Bq) time (s)

Absorbed dose (Gy)

Energy (J)

mass (kg)

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=4×10−4

0.08

= 5×10−3 𝐺𝑦

The biological effects of radiation All ionising radiation can cause damage to the body. There is no minimum amount of radiation which is safe. The risk of biological harm from an exposure to radiation depends on:

1) the absorbed dose 2) the kind of radiation 3) the body organs or tissue exposed

Radiation weighting factor The body tissue or organs may receive the same absorbed dose from alpha or gamma radiation, but the biological effects will be different. To solve this problem a radiation weighting factor (wR) is used. This is a number given to each kind of radiation as a measure of its biological effect. Some examples are given below.

Type of radiation Radiation Weighting

Factor (WR)

Alpha particles 20

Beta particles 1

Gamma rays 1

Protons 5

Fast neutrons 10

Slow neutrons 5

Equivalent dose

Equivalent dose is an effective quantity for analysing the effect of radiation because it takes account of both the absorbed dose and the type of radiation absorbed. Equivalent dose (H) is calculated by the product of absorbed dose (D) and radiation weighting factor. Equivalent dose is measured in Sieverts (Sv).

H = D wR Equivalent dose (Sv)

Absorbed Dose (Gy)

Radiation

weighting factor

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Example

A worker in the nuclear industry receives the following absorbed doses in a year. 30 mGy from gamma radiation, wR = 1 300 mGy from fast neutrons, wR = 10 Calculate the equivalent dose that the worker receives for this year.

H = DwR

for gamma H = 30 x 10-3 x 1 = 30 x 10-3 Sv for neutrons H = 300 x 10-6 x 10 = 3.0 x 10-3 Sv total H = 30 x 10-3 + 3.0 x 10-3 = 33 x 10-3 Sv or 33 mSV Equivalent Dose Rate

The time of exposure (t) to ionising radiation is also important. An equivalent dose of 100 mSv

received in one day is more dangerous than the same equivalent dose received over the course of

one year.

State that the equivalent dose rate(Ḣ) is the equivalent dose(H) per unit time(t).

Ḣ = H / t

Background radiation Everyone is exposed to background radiation from natural and from man-made radioactive material. Background radiation is always present. Some of the factors affecting background radiation levels are:

• Rocks which contain radioactive material, expose us to ionising particles • Cosmic rays from the sun and outer space emit lots of protons which cause ionisation in our atmosphere • Building materials contain radioactive particles and radioactive radon gas seeps up from the soil and collects in buildings, mainly due to lack of ventilation. • The human body contains radioactive potassium and carbon • In some jobs people are at greater risk. Radiographers exposed to X-rays used in hospitals and nuclear workers from the reactor.

Natural radiation is by far the greatest influence on our exposure to background radiation.

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Examples Natural Source Annual Equivalent

Dose (mSv) Artificial Source Annual Equivalent

Dose (mSv)

From Earth Cosmic Food Buildings (radon gas)

0.4 0.3

0.37 0.8

Medical Weapons (fallout) Occupational (nuclear power and hospitals) Nuclear discharges

0.25 0.01

0.01

0.002

Total natural 1.87 Total artificial 0.272

The individual values above do not need to be memorised. However, you do need to learn the following values:

• Average annual background radiation in the UK is 2.2 mSv.

• Annual effective dose limit for a member of the public is 1 mSv.

• Annual effective dose limit for a radiation worker is 20 mSv.

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HALF-LIFE AND SAFETY Half-life Radioactive decay is a random process. This means that for a radioactive source, it can never be predicted when an atom is about to decay. In any radioactive source, the activity decreases with time because the number of unstable atoms gradually decreases leaving fewer atoms to decay. The half-life of a radioactive source is the time for the activity to fall to half its original value. Examples 1. A Geiger-Muller tube and ratemeter were used to measure the half-life of radioactive caesium-140. The activity of the source was noted every 60 s. The results are shown in the table. By plotting a suitable graph, find the half-life of caesium-140. Time (s) 0 60 120 180 240 300 360

Count Rate (counts/s) (corrected for background)

70 50 35 25 20 15 10

From the graph the time taken to fall from 70 counts/s to 35 counts/s = 120 s 35 counts/s to 17.5 counts/s = 120 s Average half life of caesium-140 = 120 s.

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250 300 350 400

Co

rrec

ted

Co

un

t R

ate

(co

un

ts/s

eco

nd

)

Time (s)

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2. The activity of a source falls from 80 MBq to 5 MBq in 8 days. Calculate its half-life.

80 → 40 → 20 → 10 → 5 4 half-lives (count the arrows) = 8 days Half life of source = 8/4 = 2 days Reducing the equivalent dose The equivalent dose that you receive from a radioactive source can be reduced by:

1. Shielding 2. Limiting the time of exposure 3. Increasing the distance between you and the source

Examples Shielding

• Keeping all radioactive materials in sealed containers made of thick lead.

• Wear protective lead aprons to protect the trunk of the body.

• Dentists may stand behind a lead screen while a patient is having an x-ray.

Limiting exposure time

• Only use the source when you have to. Store it away when not in use

• Dentists and doctors will leave the room while patients are being x-rayed Increasing distance

• Keep as far away from the radioactive materials as possible o Hold source at arms’ length o Use tongs

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NUCLEAR FISSION There are two types of nuclear fission:

• Spontaneous fission

• Induced fission

Fission is when a heavy nucleus disintegrates (splits), leaving two nuclei of smaller mass number

(fission fragments) plus some neutrons. Energy is normally released in the fission process.

Spontaneous fission happens when the nucleus is unstable and the nucleus splits naturally.

Induced fission is when a heavy nucleus is bombarded with neutrons. The neutrons cause the heavy

nucleus to split.

Fission Chain Reaction The neutrons released from a fission reaction can induce further fissions in nuclei. This process is called a chain reaction. A chain reaction releases huge amounts of energy and must be controlled in a nuclear reactor.

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NUCLEAR FUSION A fusion reaction is where two light nuclei join together (fuse) to form a heavier nucleus. Like fission, energy is normally released as the result of a fusion reaction.

(www.windows2universe.org)

The light nuclei require large amounts of energy in order to fuse together. This is why it is difficult to

generate fusion reactions in science labs.

Plasma Containment

Containment is the major problem facing fusion research. At 40,000,000 K, everything is a gas. The best ceramics developed for the space program would vaporize when exposed to this temperature.

Because the plasma has a charge, magnetic fields can be used to contain it — like a magnetic bottle. But if the bottle leaks, the reaction won’t take place. And scientists have yet to create a magnetic field that won’t allow the plasma to leak.

A working fusion reactor is a major goal for physics research. A fusion reactor only requires isotopes

of hydrogen as fuel and the only radiation released are neutrons which are easily absorbed.

There would be no radioactive waste produced unlike with fission reactors.

Fusion reactions occur at the core of stars and are responsible for the energy produced by a star.

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Nuclear Power

Uranium or plutonium fuel can be used in nuclear reactors to generate heat by fission. The heat

generated by fission can be used to heat water to generate steam which drives electrical generators

to produce electrical energy.

Advantages of Nuclear Power

• Nuclear power stations produce a large amount of energy for a small amount of fuel

• There are no carbon dioxide or sulphur dioxide emissions from a nuclear power station

Disadvantages of Nuclear Power

• Radioactive waste o Has to be stored in lead-lined barrels and put into underground caves o Seals must be checked every 30 years or so to test for possible leakage

• Risk (albeit very small) of a catastrophic nuclear accident (Chernobyl, 1986, Fukishima, 2011)