Question

A metre-long tube open at one end, with a movable piston at the other end, shows resonance with a fixed frequency source (a tuning fork of frequency 340Hz ) when the tube length is 25.5cm or 79.3cm. Estimate the speed of sound in air at the temperature of the experiment. The edge effects amy 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 note and the third harmonic `(79.3 cm` is about 3 times 25.5 cm ).
In the fundamental mode, `(lambda)/(4)=l_(1)=25.5`
`lambda=4xx25.5 =102cm=1.02m. `
Speed of sound in air, `upsilon =vlambda =340xx1.02=346.8m//s`