Question

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

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

Answer 1

Answer: (C)

Third

Answer 2

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.