Question

A clindrical wavefront is spreading out from a line source such as a long narrow slit.When the wavefront is at a distance r from the source,the amplitude is proportional to
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Answer 1

Explanation:

The intensity related to wave varies as (1/r^2). Also, intensity is proportional to square of amplitude(A^2). So, A varies as (1/r).

Answer 2

The amplitude is proportional to $\bf\frac{1}{r}$.

• In a cylindrical wavefront, the source is usually infinitely long like the long narrow line source given in the question.
• The intensity of this wavefront is proportional to $\frac{1}{r^2}$ where r is the distance from the source.
• For a wave, the amplitude is proportional to the square root of the intensity of the wave.
• Hence the amplitude of a cylindrical wavefront will be proportional to  $\sqrt{\frac{1}{r^2} }= \frac{1}{r}$.

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