Question

If amplitude of waves at distance r from a point source is A, the amplitude at a distance 2r will be ?​

Answer 1

Answer:

The amplitude will be A = . We know that, Intensity is inversely proportional to the square of the distance

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Answer 2

A point source produces a spherical wave assuming medium is isotropic(air).

Wave energy is conserved as it propagates through air. In a spherical pressure wave of radius r, the energy of wavefront is spread out over the spherical surface area i.e. 4πr squared.

Therefore, the energy per unit area of an expanding spherical wave decreases as 1/r squared (Spherical Spreading Loss).

Since energy is proportional to amplitude squared, an Inverse Square Law for energy translates to 1/r decay law for amplitude.

Crux: Amplitude at 2r should be A/2.