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Question:

A person blows into the 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, what happens?

a high pressure pulse starts traveling up the pipe, if the other end of the pipe is open.

a low pressure pulse starts traveling up the pipe, if the other end of the pipe is open.

a low pressure pulse starts traveling up the pipe, if the other end of the pipe is closed.

a high pressure pulse starts traveling up the pipe, if the other end of the pipe is closed.

Solution:

At the open end, the phase of the pressure wave changes by π radian due to the reflection. At the closed end, there is no change in the phase of a pressure wave due to reflection.