# Derive the frequency for a third harmonic in a closed pipe from f=v/lamda ?

Jul 22, 2018

$f = \frac{3 v}{4 L}$

#### Explanation:

Well let's see, we know that frequency is equal to:
$f = \frac{v}{l} a m \mathrm{da}$

We also know that the wavelength at a third harmonic in a closed pipe is:
$L = \frac{3}{4} l a m \mathrm{da}$

$L$ is the length of the pipe

Isolate lamda:
$\frac{4}{3} L = l a m \mathrm{da}$

Substitute for wavelength in the first equation:
$f = \frac{v}{\frac{4}{3} L}$

$f = \frac{3 v}{4 L}$