ELECTROMAGNETIC
SPECTRUM
Ø Electromagnetic
waves are transverse waves. They result from the oscillating magnetic
and electric fields at right angles to each other.
Ø Electromagnetic
spectrum is the arrangement of the waves in order of their wavelengths or
frequencies.
Ø The
spectrum consists of the following waves;
|
GAMMA …………..HIGH FREQUENCY (HAI FAI) - George and
X-RAYS……………. - Xenon
ULTRAVIOLET……… - Undermined
VISIBLE LIGHT……… – VIolas
INFRARED…………….. - INFormation and
MICROWAVES……….. - MIssed
RADIOWAVES……HIGH
WAVELENGTH (HAWA WOTE) - RADon
Properties of electromagnetic waves
Ø They
travel through space at the speed of light c= 3.0 x 10 8 m/s.
Ø They
do not require a medium for their transmission.
Ø They
are transverse waves in nature.
Ø They
undergo interference, reflection, diffraction, refraction and polarization
effects.
Ø They
possess energy in different amounts according to the relation E=hf.
Ø They
carry no charge. Thus they are not affected by the magnetic or the electric
field.
Production
and detection of electromagnetic waves
-
Gamma
rays
Ø Production-
they are emitted by radioactive substances.
This results from the energy changes occurring in the nuclei of the
radioactive elements.
Ø Detection-
photographic plates, radiation detectors.
E.g. the G-M tube.
-
X-rays
Ø Production-
produced in an x-ray tube when fast moving electrons are suddenly stopped by a
metal target.
Ø Detection-
fluorescent screens and photographic films.
- Ultraviolet radiation
Ø Production-
produced by the sun, sparks and mercury vapor lamps, due to large changes in
the electrons of an atom.
Ø Detection-
photographic films, photocells, fluorescent materials (e.g. quinine sulphate), paper
lightly smeared with Vaseline.
-Visible light
Ø Production-
the major source is the sun. Others include; hot objects, lamps, laser beams.
Ø Detection-
the eye, photographic film, photocell.
- Infrared radiation
Ø Production-
produced by the sun, fires or hot bodies due to small energy changes in an atom
or molecular vibration.
Ø Detection-
by the skin, a thermopile, bolometer, and thermometer with blackened bulb.
-
Microwaves
Ø Production-
produced by magnetrons in microwaves or maser.
Ø Detection-
crystal detectors and solid state diodes.
-
Radio
waves
Ø Production-
produced by oscillating electrical circuits and transmitted through the
antennae (aerials).
Ø Detection-
resonant circuits in radio receivers with diodes and earphones.
APPLICATIONS
OF ELECTROMAGNETIC WAVES
1.
GAMMA
RADIATION
a) Used in medicine
- to sterilize medical equipments
-Killing cancerous and other malignant
growths in bodies.
b) in industries
- to detect flaws in metals
2.
X-RAYS
a) Applied
in medicine- in photography/ radiography – to identify the nature of the
internal structure e.g. the bones and check any accidentally swallowed pins or
lodged bullet.
b) Cancer
therapy- has the ability to kill malignant tissues.
c) Crystallography-
study the structure of crystals.
d) In
industries to detect flaws in metals; in addition detecting forgeries in arts.
e) Controlling
germs and pests through irradiation.
3.
ULTRAVIOLET
RADIATION
a) Used
in spectroscopy and mineral analysis.
b) To
detect forgeries.
c) Fluorescent
materials are mixed with washing powders so that clean clothes seem brighter
when exposed to the sun due to ultraviolet radiation of the sun. Because U.V it
causes fluorescing.
d) In
medicine- to kill bacteria. It’s also used in skin treatment. As a source of
vitamin D.
e) In
food technology- to detect the freshness of an egg.
f) In
industries – used with photocells.
4.
VISIBLE
LIGHT
a) Enables
the eye to see
b) Used
in ordinary photography, optical fibres and laser (light amplification by the
stimulated emission of radiation) beams.
5.
INFRARED
a) Used
in cooking, heating and drying
b) In
agriculture- to warm green houses
c) In
infrared photography and heat- seeking missiles.
6.
MICROWAVES
a) Used
in radar (radio detection and ranging) communication. - locates ships and aero
planes.
b) Used
also in cooking.
Magnetron
produces microwaves at a frequency of about 2,500 MHZ. They are directed by the
metal guider and distributed throughout the oven by the rotating metal stirrer.
Microwaves heat up water and fat molecules therefore cooking the food. The
turntable rotates. The wire mesh reflects back the microwaves.
Qn: why should the device be
switched off before opening the door?
Microwave Oven
In a microwave oven, a magnetron tube produces a beam of
microwaves that are scattered throughout the interior of the oven by a metal
fan called a stirrer. The microwaves pass through most materials easily, but
they are absorbed by water. The water molecules begin to vibrate rapidly and
produce heat, which in turn cooks the food. Microwave ovens are much more
efficient at heating food than conventional ovens and therefore use less
energy.
© Microsoft Corporation. All Rights Reserved.
Microsoft
® Encarta ® 2009.
© 1993-2008 Microsoft Corporation. All rights reserved.
7.
RADIOWAVES
-
Medium waves (MW) and short wave (SW)
are used to transmit radio signals.
-
Amplitude Modulation (AM) have a longer
range of transmission because of the reflection by the ionosphere.
-
TV and FM (Frequency modulation) have
short ranges.
-
VHF (Very high frequencies) is used in
TV and FM radio and is transmitted directly from the transmitter.
HAZARDS OF SOME ELECTROMAGNETIC
WAVES
- U.V radiations, x –rays and gamma
radiations have very high energy and are likely to cause damage to body cells,
skin burn or affect the eye when absorbed in large doses.
- delayed effects of radiations
such as cancer, leukemia, hereditary defects in children.
Minimizing
the dangers
-
Reducing the dosage by shielding.
-
Keeping safe distance from the source.
-
Minimizing exposure time.
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