A source of sound of frequency $256 Hz$ is moving rapidly towards a wall with a velocity of $5m/s$. The speed of sound is $330 m/s.$ If the observer is between the wall and the source, then beats per second heard will be .... $Hz$
Diffcult
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(a) The observer will hear two sound, one directly from source and other from reflected image of sound
Hence number of beats heard per second
=$\left( {\frac{v}{{v - {v_S}}}} \right)\,n - \left( {\frac{v}{{v + {v_S}}}} \right)\,n$
= $\frac{{2nv{v_S}}}{{{v^2} - v_S^2}} = \frac{{2 \times 256 \times 330 \times 5}}{{335 \times 325}} = 7.8 Hz$
Hence number of beats heard per second
=$\left( {\frac{v}{{v - {v_S}}}} \right)\,n - \left( {\frac{v}{{v + {v_S}}}} \right)\,n$
= $\frac{{2nv{v_S}}}{{{v^2} - v_S^2}} = \frac{{2 \times 256 \times 330 \times 5}}{{335 \times 325}} = 7.8 Hz$
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