2. ELECTROMAGNETIC SPECTRUM
The orderly arrangement of EM waves in increasing or
decreasing order of wavelength or frequency is called
electromagnetic spectrum. The range varies from 10^-12m
to 10^4 m, i.e.. From gamma-rays to radio waves.
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3. VISIBLE RAYS
It is the part of the spectrum which is visible by human
eye and Its frequency range is from 4×10^14 Hz to 7×10^14
Hz
Uses of visible rays are given below
Visible rays are used by the optical oranges of Humans
and animals for three primary purpose given below:
1. To see things, avoid bumping from them and escape
danger
2. To find stuff to eat
3. To find other living with which to consort so as to
prolong the species
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4. ULTRAVIOLET RAYS
These rays were are discovered by Ritter in 1801.These rays
are produced by special lamps and very hot bodies. The sun
an important source of UV-rays but fortunately absorbed by
ozone layer at an altitude of about 40-50km. Its frequency
range is from 10^14 Hz to 10^16.
Uses of ultraviolet rays are given below:
◦ These are used in burglar alarm.
◦ These are used in checking mineral sample.
◦ These are used to study molecular structure.
◦ To kill germs in minerals.
◦ To sterilise surgical instruments.
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6. X-RAYS
These rays were discovered by German professor
Roentgen. Its frequency range is from 3 x 10^16 Hz to
3x10^21 Hz.
Uses of X-rays are given below:
(i) These are used in surgery to detect the fracture,
diseased organs, stones in the body, etc.
(ii) These are used in engineering to detect fault, crack on
bridges, testing of welds.
(iii) These are used at metro station to detect metal or
explosive material.
(iv) These are used in scientific research. 6
8. GAMMA-RAYS
These rays were discovered by Rutherford. They travel
with the speed of light and having high penetration
power. The frequency ranges from 3 x 10^18 Hz to 5 x 10^22
Hz.
Uses of gamma rays are given below::
(i) These are used to produce nuclear reaction.
ii) These are used in radio therapy for the treatment of
tumour and cancer.
(iii) These are used in food industry to kill pathogenic
microorganism
iv) These are used to provide valuable information about8
