Assertion :A train is approaching towards a hill. The driver of the train will hear beats. Reason: Apparent frequency of reflected sound observed by driver will be more than the frequency of direct sound observed by him.
A
Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
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B
Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
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C
Assertion is correct but Reason is incorrect
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D
Assertion is incorrect but Reason is correct
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Solution
The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion The frequency received by the stationary hill will be more than the frequency emitted by train due to Doppler Effect. Now this sound will act as a stationary source of sound when reflected upon the hill and travels to be observed by the moving train.
Hence, again the frequency would further increase in accordance with Doppler Effect.
The difference in the frequencies of the two sounds, one direct and one after the echo will give the beat frequency of the sound.