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

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,
  1. a high-pressure pulse starts travelling up the pipe, if the other end of the pipe is open.
  2. a low-pressure pulse starts travelling up the pipe, if the other end of the pipe is open.
  3. a low-pressure pulse starts travelling up the pipe, if the other end of the pipe is closed.
  4. a high-pressure pulse starts travelling up the pipe, if the other end of the pipe is closed.

Solution

When a sound pulse is reflected from open end of a pipe, phase changes by $180^{\circ}$. A high pressure pulse i.e., compression is reflected as a low pressure pulse i.e., rarefaction. When sound pulse is reflected through a rigid boundary (closed end of a pipe), no phase change occurs so a high pressure pulse is reflected as a high pressure pulse. `

Asked in: JEE Advanced 2012 (Paper 1)

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