Question

A metre- long tube open at one end,with a movable pistonat the other end, shows resonance with a fixed frequency source(a tuning fork of frequency 340 Hz) when the tube length is 25.5cm or 79.3 cm.Estimate the speed of sound in air at the temperature of the experiment.The edge effect may be neglected.

Answer 1

As there is a piston at one end of the tube, it behaves as a closed organ pipe, which produces odd harmonics only . Therefore the pipe is in resonance with the fundamental more a the third harmonic ( 79.3 cm is about 3 times 25.5 cm )
In the fundamental note `( lambda) /( 4) = l_(1) = 25.5 `
`lambda= 4 xx 25.5 = 102 cm = 1.02 m `
Speed of sound in air.
`v = v lambda =340 xx 1.02 `
`=346.0 m //s `