1. ELECTROMAGNETIC SPECTRUM
Uses and harmful effects

2. At the end of the topic you should be able to…
state that all electromagnetic waves are transverse waves that travel with the same high speed in vacuo and state the magnitude of this speed
describe the main components of the electromagnetic spectrum
discuss the role of the following components in the stated applications:
radiowaves in radio and television communication
microwaves in satellite television and microwave oven
infra-red waves in infra-red remote controllers and intruder alarms
light in optical fibres for medical uses and telecommunications
ultra-violet in sunbeds, and sterilisation
X-rays in radiological and engineering applications
Gamma rays in medical treatment
describe the effects of absorbing electromagnetic waves, e.g. heating, ionisation and damage to living cells and tissue

3. Electromagnetic Spectrum

4. Properties
An electromagnetic wave is produced by the simultaneous vibration of electric and magnetic fields.
All electromagnetic waves
transfer energy from one place to another
are transverse waves
can travel through vacuum. They DO NOT require any medium to travel from one point to another.
travel through a vacuum at the speed of 3 x 108 ms-1.
obey wave properties like reflection and refraction.
carry no electrical charge as they are neither positively nor negatively charged.
obey the wave equation: v = f.

5. If electromagnetic waves travel in vacuum, then for the wave equation
v = f
v = c,
where c is the symbol for the speed of light in vacuum
 c = f
 3.0 x 108 = f
Their frequencies do not change when they travel from one medium to another. (e.g.. From water to glass). This is because their frequency ƒ depends only on the source of the wave. Only their speeds and wavelengths change from one medium to another.

6. Electromagnetic spectrum Electromagnetic Spectrum
Components of electromagnetic spectrum
Electromagnetic Spectrum
Gamma rays
X-rays
Ultraviolet
Visible light
Infrared
Microwave
Radio wave
long wavelength
short wavelength
Several km
< m
high frequency
low frequency
Speed in a vacuum
is constant
c = 3 x 108 m s-1
“Ronald McDonald Is Very Ugly eXcept Gary”

7. Applications of electromagnetic spectrum
For each component, you need to know
Range of wavelength
Its uses
Any harmful effects (The higher the frequency, the larger the amount of energy)
Source
Detector

8. Radio wave has wavelength of 10-1 to 105 m Can move around obstacles
is used in radio communication and television transmission over long distances (LW, MW, SW, VHF, UHF). Radio telescope.
source: TV and radio transmitters
detector: aerials of TV and radio receivers/antenna
Television transmission is made possible with the use of VHF and UHF radio waves

9. speed-monitoring radar
Microwave
has wavelength of 10-3 to 10-1 m (0.001 m to 0.1m)
is used in satellite communication and transmission, radar systems and microwave cooking/microwave oven
travels in straight line without losing much of its energy
source: electronic devices (eg. cavity magnetron in microwaves)
detector: microwave receivers
speed-monitoring radar
satellite station

10. an infra-red photograph
Infrared radiation
is the radiation beyond the red end of the visible spectrum
has wavelength of 10-7 to 10-3 m
is used in remote control devices, intruder alarms, infra-red photography and radiant heaters
is emitted by hot objects
source: warm bodies
detector: special photographic films, blackened thermometers and thermocouples
an infra-red photograph

11. Visible light can be seen by human eye
has wavelength of 4 x 10-7 to 7 x 10-7 m
is used in optical fibres, medical usage, telecommunications, chemical spectral analysis and photosynthesis, endoscopy. Lasers for medical, industrial and surveying use.
source: hot bodies, lasers and sun
detector: eyes, photographic film and photocells
laser surgery

12. Ultraviolet radiation
has wavelength of 10-8 to 10-7 m
stimulates our bodies to produce vitamin D
Can cause tanning, overexposure can lead to skin cancer
is used in sunbeds, fluorescent tubes, sterilisation, forgery detection and fluorescence in washing powders
source: sun, mercury vapour and lamps
detector: photographic film, fluorescent screens, dyes and photocells
overexposure to UV radiation can cause skin cancer

13. x-ray photograph of hand
has wavelength of to 10-8 m
is penetrating and can cause damage to tissues and organisms
Doctors, nurses and people working in X-ray environment have to wear protective clothing to shield themselves from X ray
is used in medical and dental diagnostic tools and engineering applications. Check for flaws/cracks in metals. Detect artwork forgery. Airport scanners. Crystal structure analysis.
source: x-ray tubes
detector: photographic film and fluorescent screens
x-ray photograph of hand

14. Gamma ray (HIGHEST ENERGY!!!!, HIGHEST FREQUENCY)
has wavelength of to m
is penetrating and can cause damage to living tissues and organisms
is used in treatment of cancer (gamma knives – sharp beam of gamma ray) and checking of welds, under controlled situations. Sterilising equipment.
source: cosmic rays, radioactive substances and nuclear reaction
detector: Geiger-Müller counters (GM tube), bubble/cloud chambers and photographic film

15. Effects of EM Waves on Cells and Tissue
Exposure to electromagnetic radiation primarily causes heating effects such as the pain of sunburn or skin cancer. However, over-exposure may result in harmful effects such as pain of sunburn or skin cancer.
EM waves can be classified as either ionising radiation or non-ionising radiation:
Ionising radiations are extremely high frequency EM waves which include X-rays and gamma rays. They have enough photon energy to produce ionisation (a process where one or more electrons are removed from a neutral atom by radiation). It is a harmful process leading to destruction or modification of living cells.
Non-ionising radiations are the part of the EM spectrum which has photon energies too weak to produce ionisation. Examples are ultra-violet, visible light, infra-red radiation, microwave and radio wave.

16. Memory aid (song) for Electromagnetic Spectrum

17. Electromagnetic waves
consist of
Components
Radio waves
Microwaves
Infra-red waves .
Light
Ultra-violet
X-rays
Gamma rays
Applications
Radio and television communication
Satellite television and telephone
Home electrical appliances, remote controls and intruder alarms
Optical fibres in medical usage and telecommuncation
Sunbeds, fluorescent tubes and sterilisation
Medical use and engineering applications
Medical treatment
are
Transverse waves
with speed in vacuum
c = 3 x 108 m s-1

18. Reference: