JEE Advanced 2012 Physics question

A person blows into open-end of a long pipe. As a result, a high-pressure pulse of air travels down the pipe. When this pulse reaches the other end of the pipe,

(A)a high-pressure pulse starts traveling up the pipe, if the other end of the pipe is open.
(B)a low-pressure pulse starts traveling up the pipe, if the other end of the pipe is open.Correct
(C)a low-pressure pulse starts traveling up the pipe, if the other end of the pipe is closed.
(D)a high-pressure pulse starts traveling up the pipe, if the other end of the pipe is closed.Correct

Answer: (B),(D)

Solution

At an open end the pressure must remain atmospheric (pressure node); a compression arriving there is reflected with a phase change of π in pressure, i.e. as a rarefaction (low-pressure pulse): (B) true, (A) false.

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Question ID VK-026018