Question

In $1m$ long open pipe what is the harmonic of resonance obtained with a tuning fork of frequency $480Hz$ ?

• A. First
• B. Second
• C. Third
• D. Fourth

Answer 1

Answer: (C)

For an open pipe of length $l$, the frequency $n$ is given by
$n=n^{\prime }\frac{v}{2l}$
where $v$ is velocity of sound, $n$ the overtone.
Given, $n=480Hz$ and $l=1m$,
and $v=330m{s}^{-1}$
$n^{\prime }=\frac{n(2l)}{v}$
$=\frac{480\times 2\times 1}{330}=2.9\approx 3$
Hence, this is the second overtone or third harmonic.