As a wave propagates

Options

A. the wave intensity remains constant for a plane wave.
B. the wave intensity decrease as the inverse of the distance from the source for a spherical wave.
C. the wave intensity decreases as the inverse square of the distance from the source for a spherical wave.
D. total intensity of the spherical wave over the spherical surface centred at the source remains constant at all times.

Answer

A, C, D

Explanation

For a plane wave, intensity (energy crossing per unit area per unit time) is constant at all points. But for a spherical wave, intensity at a distance `r` from a point source of power `(P)`, is given by
`I = (P)/(4 pi r^(2)) rArr I prop (1)/(r^(2))`
But the total intensity of the spherical wave over the spherical surface centred at the source remains constant at all times.