1. G482 Electricity, Waves & Photons
2.4.1 Wave Motion
EM Waves
2.4.3 Interference
2.4.4 Stationary Waves
Ks5 OCR Physics H158/H558
Index
Mr Powell 2012

2. 2.4.2. Electromagnetic Waves
Assessable learning outcomes.....
state typical values for the wavelengths of the different regions of the electromagnetic spectrum from radio waves to X-rays;
state that all electromagnetic waves travel at the same speed in a vacuum;
describe differences and similarities between different regions of the electromagnetic spectrum;
describe some of the practical uses of electromagnetic waves;
describe the characteristics and dangers of UV-A, UV-B and UV-C radiations and explain the role of sunscreen (HSW 6a);
explain what is meant by plane polarised waves and understand the polarisation of electromagnetic waves;
explain that polarisation is a phenomenon associated with transverse waves only;
state that light is partially polarised on reflection;
recall and apply Malus’s law for transmitted intensity of light from a polarising filter.
Book pages

3. S
EM Spectrum
Can you remember any parts of it. Write out 1-8 in your books and test yourself? 1 2 3 4 5 6 7 8

4. Copy text
& diagram
Visible Light
Wavelength in nanometres (nm)
1x10-9 or x m
Violet
Indigo
Blue
Green
Yellow
Orange
Red
White light is dispersed by a prism to form a spectrum (not to scale)
Visible light is detected by the human eye. White light consists of ROY-G-BIV (as shown above). Each colour is a range of wavelengths and is absorbed differently by the cells in the eye.
Visible light is the middle part of the EM Spectrum sandwiched between Ultraviolet (more than violet) & Infra Red (less than red)

5. O Y V Visible Light Copy & Complete Shorter Wavelength
Infra Red
Ultraviolet
>750
<400
Higher Frequency
Wavelength in nanometres (nm)
1x10-9 or x m

6. IR R O Y G B I V UV Answers Visible Light Shorter Wavelength
Infra Red
Red
Orange
Yellow
green
Blue
Indigo
Violet
Ultraviolet
>750
<400
Higher Frequency
Wavelength in nanometres (nm)
1x10-9 or x m

7. a) state typical values for the wavelengths of the different regions of the electromagnetic spectrum from radio waves to X-rays;
The types of electromagnetic radiation are broadly classified into the following classes:
Gamma radiation
X-ray radiation
Ultraviolet radiation
Visible radiation
Infrared radiation
Terahertz radiation
Microwave radiation
Radio waves

8. a) state typical values for the wavelengths of the different regions of the electromagnetic spectrum from radio waves to X-rays;
γ= Gamma rays
MIR= Mid infrared
HF= High freq.
HX= Hard X-rays
FIR= Far infrared
MF= Medium freq.
SX= Soft X-rays
Radio waves
LF= Low freq.
EUV= Extremeultraviolet
EHF= Extremely high freq.
VLF= Very low freq.
NUV= Near ultraviolet
SHF= Super high freq.
VF/ULF= Voice freq.
Visible light
UHF= Ultra high freq.
SLF= Super low freq.
NIR= Near Infrared
VHF= Very high freq.
ELF= Extremely low freq.
Freq=Frequency

9. b) state that all electromagnetic waves travel at the same speed in a vacuum;
The wave theory of light developed into another theory about the propagation of electromagnetic waves through space with or with an medium.
This was as a result of theoretical work by James Clark Maxwell who showed mathematically in 1865 that a changing current in a wire creates waves of changing electric and magnetic fields that radiate from the wire.
Maxwell showed that the waves are transverse in nature and that the electric waves are in phase with and perpendicular to the magnetic waves as shown

10. b) state that all electromagnetic waves travel at the same speed in a vacuum;
When an AC current is applied to a wire the alternating current in a wire creates an alternating magnetic field which generates an alternating electric field which generates an alternating magnetic field further from the wire which generates an alternating electric field which generates an alternating magnetic field further yet further from the wire and so on.
Maxwell knew that the strength of the electric field depends on the permittivity of free space, 0. He also knew that the magnetic field strength depends on the equivalent magnetic constant, the permeability of free space, 0.
He showed mathematically that the speed of electromagnetic waves in free space, c, is given by (3 x 108ms-1)
0 = 8.85 × 10−12 F m−1
0 = 4 × 10−7 T m A−1

11. c) describe differences and similarities between different regions of the electromagnetic spectrum;
Wave
Wavelength
Use
Long Wave Radio
1500 m
Broadcasting
Medium Wave Radio
300 m
Short Wave Radio
25 m
FM Radio
3 m
Broadcasting and communication
UHF Radio
30 cm
TV transmissions
Microwaves
3 cm
Communication
Radar
Heating up food
Infra red
3 mm
Communication in optical fibres
Remote Controllers
Heating
Light nm
Seeing
Communicating
Ultra violet
100 nm
Sterilising
Sun tanning
X-ray
5 nm
Shadow pictures of bones
Gamma rays
<0.01 nm
Scientific research

12. c) describe differences and similarities between different regions of the electromagnetic spectrum;
Wave
Wavelength
Hazard
Prevention
Long Wave Radio
1500 m
No hazard
Medium Wave Radio
300 m
Short Wave Radio
25 m
FM Radio
3 m
UHF Radio
30 cm
Microwaves
3 cm
Heating of water in the body
Metal grid
Infra red
3 mm
Heating effect
Reflective surface
Light nm
Ultra violet
100 nm
Can cause cancer
Sun cream (or cover up)
X-ray
5 nm
Causes cell damage
Lead screens
Gamma rays
<0.01 nm
Thick lead screens or concrete

13. c) describe differences and similarities between different regions of the electromagnetic spectrum;
The Earth and all life on it has developed a tolerance & use for some parts of the EM Spectrum due to how it behaves as it passes through air.
Some parts are absorbed fully, partly or not at all.

14. c) describe differences and similarities between different regions of the electromagnetic spectrum;

15. Which word links all of these images...

16. e) describe the characteristics and dangers of UV-A, UV-B and UV-C radiations and explain the role of sunscreen (HSW 6a);
Ozone molecules are vitally important to life because they absorb the biologically harmful ultraviolet radiation from the Sun. (even in small amounts)
There are three different types of ultraviolet (UV) radiation, UV-A ( nm), UV-B ( nm), and UV-C ( nm).
UV-C is entirely screened out by ozone around 35 km altitude.
On the other hand, UV-a reaches the surface, but it is not as genetically damaging, so we don't worry about it too much.
It is the UV-B radiation that can cause sunburn and that can also cause genetic damage, resulting in things like skin cancer, if exposure to it is prolonged.
Ozone screens out most UV-b, but some reaches the surface. Were the ozone layer to decrease, more UV-b radiation would reach the surface, causing increased genetic damage to living things

17. Skin Cancer
For the two diagrams show on the right can you answer the following questions;
What part of the body is a man most at risk for?
What part of the body is a woman most at risk from?
Why is there a difference between men and women in term of the head and neck?
Why are men's legs only 15% when women's are 42%

18. Yearly Trends
Can you clearly explain the trend seen on this graph?
Can you explain why the trend might be occurring?

19. Age Trends
Can you clearly explain the trend seen on this graph?
Can you explain why the trend might be occurring?

20. UV Index
UV index depends on:
where you are in the world
the time of year
the weather
the time of day
how high up you are (the altitude)
Met Office UV index forecasts include the effects of:
the position of the Sun in the sky
forecast cloud cover
amount of ozone in the stratosphere

21. Types of Skin
Try and work out your own skin......

22. What is your risk
You can work out from the UV index and your skin type when you are in danger?
Try it out

23. Incidence of melanoma
Can you clearly explain any trend or pattern seen on this graph i.e. Highs and lows?
Can you explain why the trend might be occurring?
Europe (2002 estimates)

24. Incidence of melanoma
Can you clearly explain any trend or pattern seen on this graph i.e. Highs and lows?
Can you explain why the trend might be occurring?
World (2002 estimates)

25. Sun Creams
If you were buying sun protection lotion, what factors would be important to you? Factors to be considered:
volume
sun protection factor (SPF)
brand
price
target (adult/child)
waterproof properties
SPF means sun protection factor.
SPF = 100 ÷ % of UV radiation transmitted
If 10% is transmitted, SPF = 100/10 = 10
If 3% is transmitted, SPF = 100/3 = 33
What is the SPF of a sunscreen that transmits 5% UV radiation?

26. Example Exam Question (Basic)
The electromagnetic spectrum covers a very wide range of wavelengths, frequencies and photon energies.
(i) State the names and wavelengths for the shortest and longest electromagnetic waves.
shortest: name wavelength m
longest: name wavelength m
(4 marks)
(ii) Calculate the ratio Longest wavelength / shortest wavelength
ratio = ( 1 mark)

27. How does the intensity spread out

28. Example Exam Question (Basic)
The electromagnetic spectrum covers a very wide range of wavelengths, frequencies and photon energies.
(i) State the names and wavelengths for the shortest and longest electromagnetic waves.
shortest: name wavelength m
longest: name wavelength m
(4 marks)
(ii) Calculate the ratio Longest wavelength / shortest wavelength
ratio = ( 1 mark)
shortest: gamma (1) allow any wavelength between 10–12 and 10–16 (m) (1)
longest: radio (1) allow any wavelength between 102 and 105 (m) (1) 4
(ii) candidates ratio e.g. 104 / 10–14 = 1018 (1) 1

29. Polarisation.....

30. f,g,i) Polarisation
Create your own diagram to show this concept clearly.
Then explain it to another student.
Electric field vector
As you rotate 90 or /2 the light gradually fades
Try it with a polariser!

31. f,g,i) Polarisation Electric field vector
Create your own diagram to show this concept clearly.
Then explain it to another student.
Electric field vector

32. Imax = is the initial intensity
i) recall and apply Malus’s law for transmitted intensity of light from a polarising filter.
Malus' law, which is named after Étienne-Louis Malus, says that when a perfect polarizer is placed in a polarized beam of light, the intensity, I, of the light that passes through is given by………….
Imax = is the initial intensity
i = is the angle between the light's initial polarization direction and the axis of the polarizer.
Examples....
Angle 0 
Angle 45
Angle 90
Angle 180

33. Imax = is the initial intensity
i) recall and apply Malus’s law for transmitted intensity of light from a polarising filter.
Malus' law, which is named after Étienne-Louis Malus, says that when a perfect polarizer is placed in a polarized beam of light, the intensity, I, of the light that passes through is given by………….
Imax = is the initial intensity
i = is the angle between the light's initial polarization direction and the axis of the polarizer.
Examples....
Angle 0  I = Imax * cos (0) * cos (0) = Imax
Angle 45 or / I = Imax * cos (45) * cos (45) = 0.52 * 0.5 2 = 2 = 0.5 Imax
Angle 90 or / I = Imax * cos (90) * cos (90) = 0
Angle 180 or  I = Imax * cos (180) * cos (180) = Imax

34. f,g,i) Applications of Transverse Polarisation…
Can you research each one of these ideas and see how Polarisation has an impact. Draw out a mind map and write out the key points for each one. You only need the basic idea for the exam not the details….
Transverse Polarisation
Radio? (GCSE)
Concentration
Stress Testing
Sun Glasses
Calculator? (Extension)
G&T Sheet 12_1

35. f,g,i) Uses of Polarisation

36. f,g,i) Fishing?

37. f,g,i) Using polarisation to measure concentration
Some liquids are ‘optically active’ and rotate the electric vector.
The liquid’s concentration is proportional to the electric vector rotation.
Sugar
solution
laser
analyser
polariser
John Parkinson

38. The structure of certain plastics will show polarisation.
f,g,i) Stress Analysis
The structure of certain plastics will show polarisation.
When viewed under stress the structure polarises the light differently.
The place where stress is greatest shows a more rapid colour change.
Models can be made of complex components which are viewed with a polarising filter so engineers can design out the stresses.
John Parkinson

41. Polarisation Exam Question…. (Basic Level)
(b) Daylight passes horizontally through a fixed polarising filter P. An observer views the light emerging through a second polarising filter Q, which may be rotated in a vertical plane about point X as shown in the diagram.
Describe what the observer would see as Q is rotated slowly through 360°. (1 mark)

42. Polarisation Exam Question…. (Basic Level)
(b) Daylight passes horizontally through a fixed polarising filter P. An observer views the light emerging through a second polarising filter Q, which may be rotated in a vertical plane about point X as shown in the diagram.
Describe what the observer would see as Q is rotated slowly through 360°. (1 mark)
Answer
(b)
variation in intensity between max and min (or light and dark) (1) or
two maxima (or two minima) in 360° rotation (1)

43. Activity Ideas...
Students can discuss the purpose of using sunscreen. (HSW 6a)
The teacher can demonstrate polarisation using a metal grill for microwave and polarising filter for light.
Students can observe light reflected from a glass surface through a polarising sheet.
Students can discuss the use of polarising filters in photography and in sun glasses to reduce glare. (HSW 6a)

44. f,g,i) Calculator LCD Displays
Extension Work
Polariser filter film with a vertical axis to polarize light as it enters.
Glass with electrodes to show patterns when the LCD is turned ON.
Twisted nematic liquid crystal. Rotates light 90 or /2 when turned on.
Glass substrate with electrode film
Polarising filter film with a horizontal axis to block/pass light.
Reflective surface to send light back to viewer.
KEY Point. System allows on/off change of transmission by use of Twisted nematic liquid crystal & crossed polarisers
General Polarisation
Nematic Crystals

45. Quick Questions (From Real Exams)...
Jan 2012
6 (a) X-rays and radio waves are two examples of electromagnetic waves.
(i) Name two other examples of electromagnetic waves. [1]
(ii) State one similarity and one difference between X-rays and radio waves. [2]
(iii) Explain why X-rays are easily diffracted by layers of atoms, about 2 × 10–10 m apart, but radio waves are not. [2]
(b) On the Earth, we are all exposed to ultraviolet radiation coming from the Sun.
State one advantage and one disadvantage of UV-B radiation. [2]
(c) (i) Circle a typical value for the wavelength of an X-ray from the list below....
2 × 10–4 m × 10–7 m × 10–10 m × 10–13 m [1]

46. Markscheme

47. Practical Skills are assessed using OCR set tasks.
The practical work suggested below may be carried out as part of skill development. Centres are not required to carry out all of these experiments.
Students should gain a qualitative understanding of superposition effects together with confidence in handling experimental data.
Students should be able to discuss superposition effects and perform experiments leading to measurements of wavelength and wave velocity.
Use an oscilloscope to determine the frequency of sound.
Observe polarising effects using microwaves and light.
Investigate polarised light when reflected from glass or light from LCD displays.
Study diffraction by a slit using laser light.
Study hearing superposition using a signal generator and two loudspeakers.
Study superposition of microwaves.
Determine the wavelength of laser light with a double-slit.
Determine the wavelength of light from an LED using a diffraction grating.
Demonstrate stationary waves using a slinky spring, tubes and microwaves.
Determine the speed of sound in air by formation of stationary waves in a resonance tube.

48. Connection
Connect your learning to the content of the lesson
Share the process by which the learning will actually take place
Explore the outcomes of the learning, emphasising why this will be beneficial for the learner
Demonstration
Use formative feedback – Assessment for Learning
Vary the groupings within the classroom for the purpose of learning – individual; pair; group/team; friendship; teacher selected; single sex; mixed sex
Offer different ways for the students to demonstrate their understanding
Allow the students to “show off” their learning
Consolidation
Structure active reflection on the lesson content and the process of learning
Seek transfer between “subjects”
Review the learning from this lesson and preview the learning for the next
Promote ways in which the students will remember
A “news broadcast” approach to learning
Activation
Construct problem-solving challenges for the students
Use a multi-sensory approach – VAK
Promote a language of learning to enable the students to talk about their progress or obstacles to it
Learning as an active process, so the students aren’t passive receptors

50. Further Research.... Radio waves: Radio waves Microwaves: Microwaves
Infrared  Infrared
Visible Light: Light
Natural sources produce EM radiation across the spectrum. EM radiation with a wavelength between approximately 400 nm and 700 nm is directly detected by the human eye and perceived as visible light. Other wavelengths, especially nearby infrared (longer than 700 nm) and ultraviolet (shorter than 400 nm) are also sometimes referred to as light, especially when visibility to humans is not relevant.
Ultraviolet: Ultraviolet
X-rays: X-rays
Gamma rays: Gamma rays