Two sources P and Q produce notes of frequency 660 Hz each. A listener moves from P to Q with a speed of 1 m s⁻¹. If the speed of sound is 330 m/s, then the number of beats heard by the listener per second will be

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Accepted Answer

(1) 4. Given: two sources at 
u=660 Hz, listener moving from P towards Q at v_L=1 m s⁻¹, v=330 m s⁻¹. Idea: the listener moves away from one source and towards the other, so the two apparent frequencies shift in opposite directions and beat against each other. Away from P: 
u'=
u(v-v_L)/v. Towards Q: 
u''=
u(v+v_L)/v. 
u''-
u'=
u(2v_L)/v=(2×660×1)/(330). Beats per second =4.

Two sources P and Q produce notes of frequency 660 Hz each. A listener moves from P to Q with a speed of 1 m s⁻¹. If the speed of sound is 330 m/s, then the number of beats heard by the listener per second will be

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