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A source of sound S of frequency 500 Hz situated between a stationary observer O and a wall, moves towards the wall with a speed of 2 m/s. If the velocity of sound is 332 m/s, then the number of beats per second heard by the  observer is (approximately)-

 

Option: 1

8 Hz


Option: 2

6 Hz


Option: 3

4 Hz


Option: 4

2 Hz


Answers (1)

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\mathrm{\begin{aligned} n_1=n\left(\frac{v}{v+v_s}\right) & =500\left(\frac{332}{332+2}\right) \\ & =500\left(\frac{332}{334}\right)=497 \mathrm{~Hz} . \end{aligned}} ------------(1)

For sound reflected from the wall-

\mathrm{\begin{aligned} & n_2=n\left(\frac{v}{v-v_5}\right) \\ & n_2=500\left(\frac{3.32}{332-2}\right)=503 \mathrm{~Hz} . \end{aligned}} -------------(2)

Beat frequency \mathrm{\begin{aligned} =n_2-h_1 & =503-457 \\ & =6 \mathrm{HZ} \end{aligned}}

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Deependra Verma

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