1. National 5 Physics
Waves & Radiation

2. True or False: Can energy be transferred by waves?
Answer TRUE

3. What is meant by the frequency of a wave?
Answer
Frequency is the number of waves passing a point per second.

4. What is meant by the period of a wave?
Answer
Period is the time taken for one wave to pass a point.

5. How does the period relate to the wave’s frequency?
Answer
Period (T) is the “inverse” of frequency (f).
This means … T = 1 / f and f = 1 / T
Example
2 waves pass a point each second. So f = 2 Hz
and T = 1 / f = 0.5 s
In other words, it takes 0.5 seconds for each wave to pass.

6. What is meant by the wavelength of a wave?
Answer
The length of 1 wave which is the distance between identical points on 2 waves next to each other.
Eg) the distance from one wave crest to the next wave crest.

7. What is meant by the amplitude of a wave?
Answer
The height of the wave from the centre line (called the “line of zero disturbance”).

8. Look at the diagram below.
How many waves are drawn, in total?
Answer 6 waves

9. Look at the diagram below.
Determine the amplitude of these waves.
Answer Amplitude is the height from the centre line
so, here, amplitude = 0.2m

10. Look at the diagram below.
Determine the wavelength of these waves.
Answer 3 waves in 0.9m … so l = 0.3m

11. What equation can you use to calculate the frequency of a wave, given the number of waves passing a point in a certain time?
Answer
f = N / t
Where N = number of waves
f = frequency in Hertz (Hz)
t = time in seconds (s)

12. What is meant by the speed of a wave?
Answer
The distance covered by a wave per unit of time.
OR “the distance covered per second”.

13. The speed of waves
The speed of a wave is simply the distance which the wave crest travels in a certain time (usually 1 second).
v = speed in ms-1
t = time in s
d = distance in m
f = frequency in Hz
l = wavelength in m
v = d / t
Also…
v = f l

14. Example
Waves, of wavelength 50cm, travel the length of a 25m swimming pool. Heather counts 30 of them hitting the end of the pool over a 1 minute period .
a) Calculate the frequency of the waves.
f = ?
N = 30
t = 60s
f = N / t
= 30 / 60
= 0.5 Hz

15. 1st v = ? f = 0.5 Hz l = 0.5m v = f l = 0.5 x 0.5 = 0.25 ms-1
b) How long does it take one wave to travel the 25m length of the pool?
1st v = ?
f = 0.5 Hz
l = 0.5m
v = f l
= x 0.5
= ms-1
2nd v = 0.25 ms-1
d = 25 m
t = ?
t = d / v
= 25 / 0.25
= 100 s

16. What is meant by a transverse wave?
Answer
A wave where the oscillations happen at right angles to the direction of motion.
Oscillations are
up and down
DIRECTION of WAVE

17. Give examples of some transverse waves.
Answer
Any wave from the electromagnetic spectrum...
radio, TV, microwaves, infrared, light, ultra violet, x-rays, gamma.
and … Water waves
Oscillations are
up and down
DIRECTION of WAVE

18. What is meant by a longitudinal wave?
Answer
A wave where the oscillations happen in the direction of motion.
Oscillations are
Forwards and backwards
DIRECTION of WAVE

19. Give an example of longitudinal waves.
Answer
Sound waves … (including ultrasound).
Oscillations are
Forwards and backwards
DIRECTION of WAVE

20. What is meant by diffraction of waves?
Answer
Waves bending around obstacles.

21. What wavelengths are better at diffracting; long or short?
Answer
Long waves diffract better than short waves.

22. Explain the differences in Radio and TV reception in terms of wave diffraction?
Answer
Long waves diffract better than short waves.
Radio waves have longer wavelengths than TV waves.
So, it is easier to pick up radio signals than T.V. signals because radio waves diffract around obstacles better (due to their longer wavelength.)

23. Sound Signals as Waves on an Oscilloscope
What are the missing words below:
The pitch of a sound is determined by the __________ of the sound waves.
frequency
The volume of a sound is determined by the _________ of the sound waves.
amplitude

24. Oscilloscope Patterns for Sound Signals
Volume Changes
volume increases
amplitude increases
no. of waves stays same
Frequency Changes
frequency increases
amplitude stays the same
no. of waves increases

25. State one use of ultrasound in medicine
Ultrasounds are high frequency sound vibrations beyond the range of human hearing. What is the range of human hearing?
20Hz Hz
State one use of ultrasound in medicine
To scan and monitor a baby in the womb.
Describe how this works
Jelly is put on the mum to reduce sound reflections from skin.
Ultrasound is transmitted into the womb.
The ultrasound reflects from different parts of the baby.
The reflected ultrasound travels back to the receiver .
The computer uses the different ‘echo times’ from the different parts
of the baby to build up an image of the baby.

26. Noise Levels and Noise Pollution
Two examples of noise pollution are: 1. 2.
Pneumatic drills
Aeroplanes
… loud discos, heavy traffic, Kirsten, Heather, Shannon & Lucy 
Excessive noise can damage ___________.
hearing
Sound levels are measured in ____________
Decibels (dB).

27. Typical Sound Levels
Whisper
Normal Conversation
Danger Level
Loud disco
30 dB
60 dB
85 dB
90 dB

28. State the sections of the ELECTROMAGNETIC SPECTRUM starting with the lowest frequency.
Answer
radio, TV, microwaves, infrared, light, ultra violet, x-rays, gamma.

29. State the sections of the ELECTROMAGNETIC SPECTRUM starting with the shortest wavelength.
Answer
Gamma, x-rays, ultra violet, light, infrared, microwaves, TV, radio.

30. State the sections of the ELECTROMAGNETIC SPECTRUM starting with the lowest energy.
Answer
radio, TV, microwaves, infrared, light, ultra violet, x-rays, gamma.

31. What do all waves in the electromagnetic spectrum have in common.
Answer
They all travel at the speed of light in air, 3 x 108 ms-1..

32. The Electromagnetic Spectrum
1. State one application of lasers in medicine.
Eye surgery, removing tatoos etc…,
2. State one application of ultra violet.
Treatment of skin disorders (acne), sterilising surgical aparatus,…

33. 3. State one application of infra red.
Heat treatment for muscles, thermograms (as tumours are warmer than surrounding tissue so they give out more infra red which can be shown on thermograms.)
4. State one application of x-rays.
Detecting broken bones.
5. What is used to detect x-rays?
Photographic film. X-rays blacken the film.

34. 5. Excessive exposure to ultra violet radiation can be harmful. Why?
It can cause skin cancer.
“Tomography” is the process of taking a series of x-ray slices to build up an image.
A “CT” scan is computerised tomography.
What’s the advantage of this?
A more detailed 3-D image is made so problems can’t be hidden.
Less risk of damage to healthy cells.

35. x-ray machine photographic film bone
Label the following block diagram to show the positions of
Bone
Photographic film
X-ray Machine
x-ray
machine
photographic
film
bone

36. EM Section Source Detector Application
For each section of the e.m. spectrum you should be able to state a typical source, detector and application. Here are some suggestions …
EM Section
Source
Detector
Application
Radio & T.V.
Microwaves
Infrared
Visible Light
Ultra Violet
X-rays
Gamma
Radio / TV transmitters
Radio / TV receivers
Communications
Microwave ovens
Microwave detection circuit
Cooking food / satellite com
Human body
IR Camera
Treat muscle strains
LASER
Human eye
Eye surgery
Fluorescent material
Treat skin disorders
UV lamp
Photographic film
Detect broken bones
X-Ray Machine
Radioactive substances
Gamma camera
Treat Cancer Tumours

37. What is meant by the term REFRACTION?
Answer
Light changing speed as it enters a new medium.

38. Refraction: Air to Glass & Glass to Air
normal
normal
Air to Glass:
Light bends towards normal
Light slows down to ms-1
Light bends away from the normal
Glass to Air:
Light speeds up again.

39. Refraction – Labels for Angles
air
glass r
normal i
Label the ‘angle of incidence’, i.
This is between the incident light and the normal.
Label the ‘angle of refraction’, r.
This is between the refracted light and the normal.

40. What type of lens is this? Convex How does it affect the light?
Lenses (optional)
focus
What type of lens is this?
Convex
How does it affect the light?
It brings the rays to a focus.
What type of lens is this?
Concave
How does it affect the light?
It spreads the light out. (diverges it)

41. Describe an Experiment to find the Focal Length of a Convex Lens (optional)
1. Create a sharp image of a distant object on a white screen by moving the lens slowly out from the screen.
2. Measure the distance between the lens and the sharp image on the screen.

42. Nuclear radiation
Radiation can kill living cells (or change them).
Describe one medical application of this.
Treatment of Cancer
Sterilisation of surgical instruments

43. Radiation is easy to detect.
Describe one medical application of this.
Tracers…. Radioactive materials are put into the body and the radiation they emit is ‘followed’ around the body by a gamma camera. This is good for locating blockages.
The half life of tracers must be carefully chosen. It can’t be too short as the activity might decrease too much during the examination. It can’t be too long as the patient would then be ‘radioactive’ for a time after the examination.

44. Alpha (a), Beta (b) and Gamma (g) Radiations
Radiation can be absorbed by the medium through which it passes.
1. State the range and absorption of alpha, beta and gamma radiations.
Radiation
Range
Absorbing Material
Alpha (a)
short
Paper or 10cm of air
Beta (b)
medium
Few mm of Aluminium
Gamma (g)
long
Several cm of lead

45. 3. What is meant by the term “ionisation”?
2. Draw a simple model of an atom showing neutrons, protons and electrons.
Nucleus consisting of protons (+) and neutrons
Tiny electrons (-) in orbit around nucleus
3. What is meant by the term “ionisation”?
Ionisation is when atoms lose or gain electrons to become charged ions.

46. 4. Which type of nuclear radiation is the most
4. Which type of nuclear radiation is the most dangerous because it can cause greatest ionisation. (i.e. it can ‘rip’ electrons away from atoms of living things, mutating cells)
Alpha. This is because alpha particles are big and positive so they act like a magnet to the electrons (-) orbiting atoms.
5. Describe how an effect of radiation (on non living things) is used in a detector of radiation.
Film badges in hospitals. These are worn by staff to check exposure levels to radiation.
The radiation ‘fogs’ the film eventually. This is seen when the films are developed.

47. Activity and Half Life
The “activity” of a radioactive source tells us how many radioactive ‘particles’ it emits per second. What is the unit for activity?
Becquerels (Bq)
What happens to the activity of a radioactive source as time passes?
It decreases.
What is meant by the term “half life”.
“Half life” is the time taken for the activity of a radioactive source to halve.

48. How do you measure the “half life” of a radioactive source?
1st - Diagram
source
Geiger Muller Tube
computer
2nd – Words of Explanation
Set the computer to record the activity of the source at regular time intervals. (eg. each second, minute or hour depending on the question information).
Use the data (table or graph) to find out how long it takes for the initial activity of the source to half.

49. Calculating Half Life Example 1
A source arrives in a hospital with an activity of 1200Bq.
After 20 days the activity has dropped to 75 Bq.
Calculate the half life of the source.
1200Bq
600Bq
300Bq
150Bq
75Bq
20 days
(Each arrow link is 1 half life of time!)
4 half lives = 20 days
1 half life = 5 days

50. Example 2
A source has an initial activity of 3600 Bq and a half life of 4 hours. Calculate the activity after 12 hours.
4 h
4 h
4 h
450Bq
3600Bq
1800Bq
900Bq
12 h = 3 half life jumps
So … final activity = 450 Bq

51. Plot a graph to show this data.
Example 3
In an experiment, the following data is recorded for the activity of a radioactive source.
Time (seconds)
Activity (Bq)
224 10
172 20
112 30 86 40 56 50 43 60 28
Plot a graph to show this data.

52. axes labels units points smooth curve even scale activity (Bq)50
100
150
200
250
activity (Bq) 10 20 30 40 50 60 70
time (s)
20s
axes
labels
units
points
smooth curve
even scale
Half life = 20 s
From the graph, calculate the half life of the source….

53. The activity, A, of a radioactive source decreases with time.
The activity, A, of a radioactive source is measured in Becquerels, Bq, where 1Bq is one atom decaying per second.
The activity, A, of a radioactive source decreases with time.
The average activity A of a quantity of radionuclide is a measure of the rate at which it decays:
Mention TOTAL intentionally to reinforce the idea that SOME internal reflection will take place at all angles as will be shown.
Where N is the number of nuclei decaying
t is the time in s.

54. Activity & Dosimetry Summary
Quantity
Symbol
Unit (Unit Symbol)
Definition / comment
Equation
The number of nuclei decaying each second. Activity decreases with time. N t
Activity A
Becquerel (Bq)
A =

55. Example 1
How many nuclei decay in 1 minute if the activity of a source is 4 x 106 Bq ?
N = ?
A = 4 x 106 Bq
t = 1 min = 60 s
N = A t
= 4 x 106 x 60
= 2.4 x 108 nuclei
Mention TOTAL intentionally to reinforce the idea that SOME internal reflection will take place at all angles as will be shown. N A t

56. Absorption of Radiation
The effects of absorbed radiation depends not only on the amount of the radiation but also on the size of the object which absorbs it.
The absorbed dose, D, is the Energy, E, absorbed per unit mass, m, of the absorbing material. It is measured in grays, Gy, where 1 Gy = 1 J/kg
E in J
Absorbed dose in Gy
mass in kg
Mention TOTAL intentionally to reinforce the idea that SOME internal reflection will take place at all angles as will be shown.

57. Activity & Dosimetry Summary
Quantity
Symbol
Unit (Unit Symbol)
Definition / comment
Equation
The number of nuclei decaying each second. Activity decreases with time. N t
Activity A
Becquerel (Bq)
A =
Gray (Gy)
[mGy = x10-3 Gy]
[mGy = x10-6 Gy]
Energy (E) absorbed (in J) per kilogram (kg) of absorbing material. E
Absorbed
Dose D
D = m

58. a) Calculate the mass of the gland.
Example 2
A patient’s thyroid gland is to receive a dose of 400Gy from a source, so that 20J of energy is absorbed by the gland.
a) Calculate the mass of the gland. E D m
D = Gy
E = J
m = ?
m = E / D
Mention TOTAL intentionally to reinforce the idea that SOME internal reflection will take place at all angles as will be shown.
= 20 / 400
= kg

59. Example 2 (cont.)
b) If the same energy has to be absorbed by a gland of mass 0.08kg, what absorbed dose will this gland receive? E D m
D = ?
E = J
m = kg
D = E / m
Mention TOTAL intentionally to reinforce the idea that SOME internal reflection will take place at all angles as will be shown.
= 20 / 0.08
= Gy

60. Typical Radiation Weighting Factor (wR )
The risk of biological harm from an exposure to radiation depends on:
The absorbed dose (D) – i.e absorbed energy per kg mass.
The type of radiation, e.g. a, b, g or slow neutrons.
The body organs or tissues exposed!
A radiation weighting factor, wR, is given to each type of radiation as a measure of its biological effect. (wR was formerly known as the quality factor given the symbol, Q.)
Mention TOTAL intentionally to reinforce the idea that SOME internal reflection will take place at all angles as will be shown.
Type of Radiation
Typical Radiation Weighting Factor (wR )
Alpha (a) 20
Beta (b) 1
Gamma (g)
X-rays
Slow neutrons
2.3

61. Activity & Dosimetry Summary Radiation weighting factor
Quantity
Symbol
Unit (Unit Symbol)
Definition / comment
Equation
The number of nuclei decaying each second. Activity decreases with time. N t
Activity A
Becquerel (Bq)
A =
Gray (Gy)
[mGy = x10-3 Gy]
[mGy = x10-6 Gy]
Energy (E) absorbed (in J) per kilogram (kg) of absorbing material. E
Absorbed
Dose D
D = m
A weighting allocated to each type of radiation to indicate its biological effect.
-----
Radiation weighting factor wR
-----

62. Equivalent Dose
Note:- In past papers and books Equivalent Dose will appear as Dose equivalent. This change will affect all papers from 2006 onwards.
The equivalent dose, H, measured in sieverts, Sv, takes into account the type and energy of the radiation. This indicates the biological effect regardless of type of radiation.
(eg. 20Sv of ALPHA is equally as harmful as 20Sv of GAMMA)
(BUT… 20Gy of ALPHA is 20 x MORE harmful than 20Gy of GAMMA)
The equivalent dose is calculated using:
Absorbed dose in Gy
Mention TOTAL intentionally to reinforce the idea that SOME internal reflection will take place at all angles as will be shown.
H = D wR
Equivalent dose in Sv
Weighting factor

63. Activity & Dosimetry Summary Radiation weighting factor
Quantity
Symbol
Unit (Unit Symbol)
Definition / comment
Equation
The number of nuclei decaying each second. Activity decreases with time. N t
Activity A
Bequerel (Bq)
A =
Gray (Gy)
[mGy = x10-3 Gy]
[mGy = x10-6 Gy]
Energy (E) absorbed (in J) per kilogram (kg) of absorbing material. E
Absorbed
Dose D
D = m
A weighting allocated to each type of radiation to indicate its biological effect.
-----
Radiation weighting factor wR
-----
Sieverts (Sv)
[mSv = x10-3 Sv]
[mSv = x10-6 Sv]
An indication of biological effect by considering the absorbed dose AND the type of radiation.
Equivalent
Dose H
H = DwR

64. Calculate the absorbed dose.
Example 3
A worker receives an equivalent dose of 45mSv from alpha radiation (wR = 20). She worked for 40 wks at 20 hours per week.
Calculate the absorbed dose. H D wR
D = ?
H = x 10-3Sv
wR =
D = H / wR
Mention TOTAL intentionally to reinforce the idea that SOME internal reflection will take place at all angles as will be shown.
= 45 x / 20
= x 10-3 Gy

65. Past Paper Q Weighting Factor
Mention TOTAL intentionally to reinforce the idea that SOME internal reflection will take place at all angles as will be shown.

66. Past Paper Q
Mention TOTAL intentionally to reinforce the idea that SOME internal reflection will take place at all angles as will be shown.

67. Past Paper Q
Mention TOTAL intentionally to reinforce the idea that SOME internal reflection will take place at all angles as will be shown. Wr

68. We are exposed to continual background radiation.
The average annual effective equivalent dose for a person in the UK from natural sources is about 2mSV.
Exposure limits have been set to:
General public – 5mSv in addition to background count in any one year.
Radiation workers – 50mSv in addition to background count in any one year. (Workers may include –pilots, medical workers, physics teachers, as well as those that work in nuclear power plants.)
Sources of background radiation include
Cosmic radiation
Inhaled radon and daughter products
Radioactivity from rocks, soil and buildings
Radioactivity present in the human body
Mention TOTAL intentionally to reinforce the idea that SOME internal reflection will take place at all angles as will be shown.

69. Safety & Equivalent Dose
Suggest some safety precautions necessary when dealing with radioactive substances.
Use tongs (don’t touch the source), never point source at people, store in a lead box, etc…
What is the unit for “equivalent dose”?
Sieverts (Sv)
What 2 main factors determine the biological effect of radiation on living things?
The absorbing tissue and the radiation itself. (The equivalent dose takes account of the type of radiation and the energy it carries.)

70. What is meant by Nuclear Fission?
Nuclear Fission is when one large nucleus splits into 2 smaller nuclei. This process releases energy and usually some neutrons.
It can be spontaneous or induced by neutron bombardment.
Example
141 56 92 36 Kr Ba +
+ 3 + n 1 + U
235 92 +
energy n 1

71. State an Application of Nuclear Fission?
In nuclear reactors, fission processes are used to generate huge amounts of heat.
The heat turns water to steam which, in turn, turns turbines.
The turbines connect to the generator to make electricity.

72. State disadvantage of using nuclear fission to generate electricity?
Large amounts of radioactive waste are generated. Safe storage of these materials for a very long term is very important.

73. What is meant by Nuclear Fusion?
Nuclear Fusion is when two nuclei combine (or “fuse together”) to produce one larger nucleus.
Again, energy is released.
Example 2 He 1 + n H
energy 3

74. State an Application of Nuclear Fusion?
Nuclear fusion is the reaction which happens in stars to create elements.
It requires very high temperatures and pressures.

75. State why nuclear fusion is a much preferred way to generate electricity from nuclear sources.
Nuclear fusion is clean – it generates no radioactive waste materials.
Nuclear fusion can be made to happen using readily available material – water!!
So why don’t we use fusion instead of fission to generate our electricity in power stations?
Fusion requires huge temperatures and pressures. Once we find ways of making fusion happen at low temperatures, we will use fusion instead of fission! Lots of research already underway … with some success starting.