Physics
(a) Define electromagnetic spectrum.
(b) Write two uses of ultraviolet rays.
(c) Calculate the speed of electromagnetic wave in a glass slab in which its frequency is 4 x 1014 Hz and wavelength is 500 nm.
Spectrum
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Answer
(a) The orderly arrangement of electromagnetic waves in increasing or decreasing order of wavelength or frequency is called electromagnetic spectrum.
(b) Two uses of ultraviolet rays are:
- For sterilising air, surgical equipments, etc.
- For detecting the purity of gems, eggs, ghee etc.
(c) Given,
f = 4 x 1014 Hz
λ = 500 nm = 500 x 10-9 m = 5 x 10-7 m
As we know,
Velocity of wave (c) = frequency (f) x wavelength (λ)
Substituting the values in the formula above we get,
c = (4 x 1014) x (5 x 10-7) = 2 x 108
Hence,
Speed of the electromagnetic wave = 2 x 108 ms-1
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