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```ELECTROMAGNETIC
SPECTRUM
Name: ________________
Class: _________________
Index: ________________
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:
1.
2.
microwaves in satellite television and microwave oven
3.
infra-red waves in infra-red remote controllers and
intruder alarms
4.
light in optical fibres for medical uses and
telecommunications
5.
ultra-violet in sunbeds, and sterilisation
6.
X-rays in radiological and engineering applications
7.
Gamma rays in medical treatment
 describe the effects of absorbing electromagnetic waves, e.g.
heating, ionisation and damage to living cells and tissue
Electromagnetic Spectrum
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.
 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.
Electromagnetic spectrum
Components of electromagnetic spectrum
Electromagnetic Spectrum
Gamma
rays
X-rays
short
wavelength
< 10-12 m
high
frequency
Ultraviolet
Visible
light
Infrared
Microwave
wave
long
wavelength
Several
km
low
frequency
Speed in a vacuum
is constant
c = 3 x 108 m s-1
“Ronald McDonald Is Very Ugly eXcept Gary”
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
 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
with the use of VHF and UHF radio waves
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
satellite station
speed-monitoring
 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, infrared photography and radiant heaters
 is emitted by hot objects
 source: warm bodies
detector: special photographic films,
blackened thermometers and
thermocouples
an infra-red photograph
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
 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
cause skin cancer
X ray
 has wavelength of 10-13 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
Gamma ray (HIGHEST ENERGY!!!!,
HIGHEST FREQUENCY)
 has wavelength of 10-14 to 10-10 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
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
• 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 ultraviolet, visible light, infra-red radiation, microwave and radio wave.
Memory aid (song) for Electromagnetic Spectrum
Electromagnetic
waves
consist of
are
Transverse
waves
with speed in
vacuum
c = 3 x 108 m s-1
Components
Applications
communication
Microwaves
Satellite television and
telephone
Infra-red
waves .
Home electrical appliances,
remote controls and intruder
alarms
Light
Optical fibres in medical usage
and telecommuncation
Ultra-violet
.
Sunbeds, fluorescent tubes and
sterilisation
X-rays
Medical use and engineering
applications
Gamma rays
Medical treatment
Reference:
http://blogs.edf.org/climate411/2007/07/25/greenhouse_effect/