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
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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