question_answer

As a wave propagates                                                 [IIT-JEE 1999]

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 the distance from the source for a spherical wave

D)            Total intensity of the spherical wave over the spherical surface centered at the source remains constant at all times

Correct Answer: A

Solution :

 For a travelling wave, the intensity of wave remains       constant if it is a plane wave. Intensity of wave is inversely proportional to the square of the distance from the source if the wave is spherical        \[\left( I=\frac{P}{4\pi {{r}^{2}}} \right)\]            Intensity of spherical wave on the spherical surface centred at source always remains same. Here total intensity means power \[P\].