Question

is there is a relation between amplitude and intensity?

Answer 1

The intensity of a wave is defined as the amount of energy that passes though unit area perpendicular to the wave direction in unit time.

The amplitude of a wave varies in a sinusoidal manner with time whereas the intensity of the wave varies as sine squared. 

The intensity of a wave depends on its energy and the energy varies in a different way from the amplitude.

Since the variation in amplitude is simple harmonic (or a sum of simple harmonic oscillations) the energy variation with time is proportional to sine squared.

.....=>The intensity of a wave is proportional to the square of its amplitude.



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