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Isha Lohan posted an Question
October 28, 2020 • 03:48 am 30 points
  • IIT JAM
  • Physics (PH)

Question: 25/60 a source at rest sends sound waves of constant wavelength. a wall moves towards the source with a velocity of 33 cm/s. the velocity of sound in

Question: 25/60 A source at rest sends sound waves of constant wavelength. A wall moves towards the source with a velocity of 33 cm/s. The velocity of sound in the medium is 330 m/sec. What is the percentage change in wavelength of sound after reflection from the wall ? 0.1 96 2 % 0.2 9% 1%

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    Dhairya sharma Best Answer

    Let wavelength of sound at source be λ1​. So frequency is ν1​=v/λ1​ where, v=330m/s is the speed of sound in the medium. The waves get reflected by moving wall so in this case observer is moving with velocity vo​=33cm/s=0.33m/s,  After reflection the wall acts like moving source with same velocity but opposite sign vs​=−33cm/s=−0.33m/s So by Doppler effect, the frequency observed by wall is: ν2​=ν1​(v+vo​)/(v+vs​)=ν1​(330+0.33)/(330−0.33)=1.002ν1​ So, new wavelength, λ2​=v/ν2​=v/1.002ν1​=0.998λ1​ So change in wavelength is =(λ1​−λ2​)×100%/λ1​=0.002×100=0.2%

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