Question

Pressure nodes are displacement antinodes and pressure antinodes are displacement nodes . Explain in detail as it was a 4 marks question in my preboard.

Answer 1

Dear Student ,
Let us consider a standing wave in an open pipe and the air molecules will then be sitting at the open end. These molecules must be at a pressure node as the outside of the pipe is at constant (atmospheric) pressure. However, they are also totally free to move, thus they are at a displacement anti node.

The air molecules at the closed end of a pipe are at a displacement node because they cannot move past the end of the pipe. However, they will still feel the wave from the rest of the pipe which will alternately squash or push them against the solid end, and pull them away: thus they are at a pressure anti node.


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