Q. In $ 1\,m $ long open pipe what is the harmonic of resonance obtained with a tuning fork of frequency $ 480\,Hz $ ?
J & K CETJ & K CET 2005Electromagnetic Waves
Solution:
For an open pipe of length $l$, the frequency $n$ is given by
$ n = n' \frac{v}{2l} $
where $v$ is velocity of sound, $n$ the overtone.
Given, $n = 480\, Hz$ and $l = 1 \,m$,
and $ v = 330\, ms^{-1} $
$ n' =\frac{n(2l)}{v} $
$ =\frac{480 \times 2 \times 1}{330}= 2.9 \approx 3 $
Hence, this is the second overtone or third harmonic.
