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KCET2009PhysicsWaves and Sound

A stationary point source of sound emits sound uniformly in all directions in a non-absorbing medium. Two points P and Q are at a distance of 4 ~m and 9 ~m respectively from the source. The ratio of amplitudes of the waves at P and Q is

Options

  1. A3 2
  2. B4 9
  3. C2 3
  4. D9 4

Correct answer

D. 9 4

Step-by-step solution

For an isotropic point source of power P, intensity I at a distance r from it is I = P 4 r ² Since power P remains the same, I ₁ I ₂ = ( r ₂ r ₁ )²= ( 9 4 )² I A ² where A is the amplitude of a wave A ₁ ~A ₂ = I ₁ I ₂ = 9 4

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