Wave Motion 4 Question 17

16. A sound wave of frequency f travels horizontally to the right. It is reflected from a large vertical plane surface moving to left with a speed v. The speed of sound in medium is c

(1995,2M)

(a) The number of waves striking the surface per second is f(c+v)c

(b) The wavelength of reflected wave is c(cv)f(c+v)

(c) The frequency of the reflected wave is f(c+v)(cv)

(d) The number of beats heard by a stationary listener to the left of the reflecting surface is vfcv

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Answer:

Correct Answer: 16. (c)

Solution:

  1. Moving plane is like a moving observer. Therefore, number of waves encountered by moving plane,

f1=f(v+v0v)=f(c+vc)

Frequency of reflected wave,

f2=f1(vvvs)=f(c+vcv)

Wavelength of reflected wave

λ2=vf2=cf2=cf(cvc+v)



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