As a wave propagates

Options

A. the wave intensity remains constant for a plane wave
B. the wave intensity decreases as the inverse of the distance from the source for a spherical wave
C. the wave intensity decreases as the inverse square of distance form the source for a spherical wave
D. total power of the spherical wave over the spherical surface centered at the source remains costant 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.
For plane wavefront`7`

For point source
But for a spherical wave, intensity at a distance `r` from a point source of power `P` (energy transmitted per unit time) is given by

`I = (P)/(4pir^(2)` or `I prop (1)/(f)`
For a line source `I prop (1)/(r)`
because `I = (P)/(2pirL)`