Exp SPA - Chp 14 EM Spectrum

1. Electromagnetic Waves

2. Learning Objectives
a) State that all electromagnetic waves are transverse waves that travel with
the same speed in vacuum and state the magnitude of this speed
b) Describe the main components of the electromagnetic spectrum
c) State examples of the use of the following components:
i. radiowaves (e.g. radio and television communication)
ii. microwaves (e.g. microwave oven and satellite television)
iii. infra-red (e.g. infra-red remote controllers and intruder alarms)
iv. light (e.g. optical fibres for medical uses and telecommunications)
v. ultra-violet (e.g. sunbeds and sterilisation)
vi. X-rays (e.g. radiological and engineering applications)
vii. gamma rays (e.g. medical treatment)
d) describe the effects of absorbing electromagnetic waves, e.g. heating,
ionisation and damage to living cells and tissue

3. Electromagnetic Spectrum

4. How to remember EM Waves??
Electromagnetic Waves
Radio Waves
Microwaves
Infra-Red
Visible light
Ultra-violet
X-rays
Gamma Rays
Real
Men
In
Violet
Underwear (are)
eXtremely
Gorgeous

5. Properties of EM Waves
1. They transfer energy from one place to another.
2. They are transverse waves.
3. They can travel through vacuum.
4. They travel through vacuum with the
speed of light = 3.0 × 108 m/s.
5. Their speed is given by v = f (frequency) × λ (wavelength)
6. They obey the laws of reflection and refraction.

6. Relationship between f and λ
For EM waves,
v = f × λ = 3.0 × 108 m/s (constant)
If f decreases, λ must increase.
If f increases, λ must decrease.

7. Relationship between f and λ
Practice Question
A wave moving along a length of rope has a frequency of f.
Given that the speed of the wave is constant, what happens to
the wavelength of the wave when the frequency is increased to
2f?
Using the wave equation:
Wavelength of the wave will be halved when the f of the wave
doubles.
𝑣 = 2𝑓 × = 𝑓l?
l
2
𝑣 = 𝑓l

8. Relationship between f and
energy
• The greater the frequency f, the greater the energy.
• The SHORTER the wavelength
 the HIGHER the frequency
 the GREATER the energy possessed by the wave.
• So gamma rays (highest frequency) has the highest energy.

9. Uses of EM Waves

10. Uses of EM Waves
Radio waves
• Radio waves have the longest wavelengths in the
electromagnetic spectrum
• Wavelengths range from several hundred metres to a few
centimetres
Uses: to transmit sound and pictures in radio and television

11. Uses of EM Waves
Microwaves
• Microwaves are radio waves of very short wavelengths (from
10–3 m to 10–1 m)
Uses:
Satellite
communication for
satellite television,
GPS and mobile
Microwave ovens Radar
Communication

12. Uses of EM Waves
Infrared-red radiation
• These are waves just beyond the red end of the visible light
spectrum
• Wavelengths range from 10–7 m to 10–3 m
• All objects emit infra-red radiation
Uses:
Remote control
of electrical
appliances
Intruder Alarms Infra-red
photography
Radiant heater

13. Uses of EM Waves
Visible Light
• Visible light is part of the electromagnetic spectrum that the human
eye can detect.
• The various wavelength of light are classified by colours.
How to remember the colours of the visible light?
ROY G. BIV

14. Uses of EM Waves
Uses:
Optical Fibres for medical
uses and telecommunications
Lasers for medical uses and
telecommunications

15. Uses of EM Waves
Ultra-violet Radiation
• Wavelengths range from 10–8 m to 10–7 m
• Main source of ultra-violet radiation is sunlight
Uses:
Sunbeds
Sterilisation
Forgery
detection
Fluorescence
Effect

16. Uses of EM Waves
X-Rays
• wavelengths ranging from about 10-13 m (10-4 nm) to 10-8 m (10 nm)
Uses:
Medical/Dental
Inspection
Checking welds
(for cracks)
Airport Security
(Baggage check)
Radiation Therapy
(Treatment of cancer)

17. Uses of EM Waves
Gamma Rays
• Result of the decay of radioactive nuclei
• Wavelengths range from about 10-10 m to less than 10-14 m.
• Can cause serious damage when absorbed by living tissue
• They can cause mutations which lead to cancer
• Highest frequency  highest energy
Uses:
Checking welds
(for cracks)
Sterilising
equipment
Radiation Therapy
(Treatment of cancer)

18. Uses of EM Waves
Gamma Knife
The high energy gamma
rays are emitted from a
cobalt-60 source.
The rays are focused on the
brain tumour through the use
of a special protective helmet
with holes drilled in it.
1
2
Each individual beam is not
strong enough to damage
normal living tissue.
3
At the point where the beams
converge, the cumulative
energy is able to kill the
cancerous cells.
4

19. Effects of EM Waves

20. Effects of EM Waves
Ionising radiation on living matter
 Ionising radiation is radiation that has the energy to remove
electrons from atoms or molecules.
 Exposure to ionising radiation can damage biological molecules
and lead to abnormal cell division.
 This may cause cancers and/or deformities to a developing foetus.
Radiation warning symbol

21. Effects of EM Waves
Infrared Heating
 The emission of infrared radiation is what makes us feel warm when
we stand near a barbecue pit.
 We feel warm because we absorb the infrared radiation.
Heat radiating from the charcoal
is actually infrared radiation.

22. Practice Question 1
The velocity of radio waves is 3.0 × 108 m s–1. A radio station is
broadcasting at a frequency of 1.0 × 106 Hz. What is the wavelength of
the radio wave?
𝑣 = 𝑓l
3.0 × 108
= 1.0 × 106
× l
l =
3.0 × 108
1.0 × 106
= 300 m

23. Practice Question 2
Which of the following options lists the members of the electromagnetic
spectrum in order of increasing wavelength?
A Microwaves, ultraviolet, infrared, X-rays
B X-rays, ultraviolet, infrared, microwaves
C Ultraviolet, infrared, microwaves, X-rays
D Infrared, ultraviolet, microwaves, X-rays
Answer:
a) Write down the order:
b) Recall Gamma Ray has highest energy  highest f  lowest l
RMIVUXG
Highest energy
Highest f
Lowest l

24. Practice Question 3
Name three regions of the electromagnetic spectrum with lower
frequency than visible light.
RMIVUXG
Highest energy
Highest f
Lowest l

25. Practice Question 4
Do gamma rays or radio waves have a higher speed when travelling in
a vacuum?
Answer:
All electromagnetic waves have the same speed (3 × 108 m s−1) when
travelling in a vacuum.

26. QUESTIONS?
Question