question_answer

In \[1\text{ }m\]long open pipe what is the harmonic of resonance obtained with a tuning fork of frequency \[480\text{ }Hz\]?

A)  First         

B)  Second

C)  Third        

D)  Fourth

Correct Answer: C

Solution :

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