A pipe 20 cm long is closed at one end. Which harmonic mode of the pipe is resonantly excited by a source of 1237.5 Hz ? (sound velocity in air `=330ms^(-1))`

Explanation

l = 20 cm = 0.20 m, `upsilon = 330 ms^(-1)`
For a pipe closed at one end
`v = (upsilon)/(4l) = (330)/(4 xx 0.20) = 412.5 Hz`
So the harmonic mode in which the pipe will resonate is
`= (1237.5)/(412.5) = 3`
which is the frequency of its third harmonic.