Wave Motion 5 Question 19

19. 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

(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

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Answer:

Correct Answer: 19. (a, c, d)

Solution:

  1. 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 (energy transmitted per unit time) is given by

I=P4πr2 or I1r2

NOTE

For a line source l1r because, l=Pπrl



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