As a wave propagates - Vidyadip

MCQ

As a wave propagates

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
✓
The wave intensity decreases as the inverse of 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 time

✓

Answer

Correct option: C.

The wave intensity decreases as the inverse of square of the distance from the source for a spherical wave

c
A plane wave does not have any radial dependence. Thus a plane wave travels with constant intensity. Intensity of a spherical wave decreases. It is because the power in the wave is carried and constant at all radius. Intensity is power distributed over the spherical surface area.

$I=\frac{P}{4 \pi r^{2}}$

For a cylindrical wave the power is same at all distance from the source. The power is distributed over the entire surface area.

$I=\frac{P}{2 \pi r l}$

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