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.

Explanation

As the piston is attached at one end of a long tube, therefore, the pipe behaves as a closed organ pipe and produces only odd harmonics. As the pipe is in resonance with the fundamental note (l = 25.5 cm) and third harmonic (79.3 cm).
`l_(1) = 25.5` cm
Thus for fundamental note
`lambda = 4l_(1)`
`= 4 xx 25.5 cm`
= 102 cm
= 1.02 m
Speed of sound in air = V = `v lambda`
`= 340 xx 1.02`
= 346.8 m/s