Q. A longitudinal sound wave given by $P=25sin\frac{\pi }{2}\left(x - 660 t\right)$ ( $P$ is in $Nm^{- 2}$ and $x$ is in $m$ and $t$ is in $s$ ) is sent down a closed organ pipe. If the pipe vibrates in second overtone then the length of the pipe (in $m$ ) is :
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Solution: