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प्रश्न
Discuss the following case-
Observer in motion and Source at rest.
- Observer moves towards Source
- Observer resides away from the Source
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उत्तर
(a) Observer moves towards Source:
Observer moves towards Source
We can assume that the observer O moves towards the source S with velocity vo. The source S is at rest and the velocity of sound waves (with respect to the medium) produced by the source is v.
From the Figure, It is observed that both vo and v are in opposite direction. Then, their relative velocity is vr = v + vo. The wavelength of the sound wave is λ = `"v"/"f"`, which means the frequency observed by the observer O is f ‘ = `"v"_"r"/lambda`. Then
`"f"' = "v"_"r"/lambda = (("v" + "v"_0)/"v")"f"`
`= "f"(1 + "v"_0/"v")` ...(7)
(b) Observer recedes away from the Source:
If the observer O is moving away (receding away) from the source S, then velocity v0 and v move in the same direction. Hence, their relative velocity is vr = v – v0. Hence, the frequency observed by the observer O is
`"f"' = "v"_"r"/lambda = (("v" + "v"_0)/"v")"f"`
`= "f"(1 - "v"_0/"v")` ...(8)
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संबंधित प्रश्न
In discussing Doppler effect, we use the word "apparent frequency". Does it mean that the frequency of the sound is still that of the source and it is some physiological phenomenon in the listener's ear that gives rise to Doppler effect? Think for the observer approaching the source and for the source approaching the observer.
The change in frequency due to Doppler effect does not depend on
Answer briefly.
State the expression for apparent frequency when the source is stationary and the listener is
- moving towards the source
- moving away from the source
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An observer moves towards a stationary source of sound with a velocity one-fifth of the velocity of sound. The percentage increase in the apparent frequency heard by the observer will be ______.
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- the frequency of sound as heard by an observer standing on the platform is 400 Hz.
- the speed of sound for the observer standing on the platform is 350 m/s.
- the frequency of sound as heard by the observer standing on the platform will increase.
- the frequency of sound as heard by the observer standing on the platform will decrease.
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- if the observer is in front of the source.
- if the observer is behind the train.
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