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 340 Hz) when the tube length is 25.5 cm or 79.3 cm. Estimate the speed of sound in air at the temperature of the experiment. The edge effects may be neglected.

Answer 1

Concept :- when successive resonance frequencies are given we consider the twice of the length difference at which these occur to be the wavelength of the waves .

Here, length of first resonance occurs ( L1) = 25.5 cm =
Length of 2nd resonance occurs ( L2) = 79.3 cm

So, wavelength = 2 × ( L2 - L1)
= 2 × ( 79.3 - 25.5)
= 2 × 53.8
= 107.6 cm
= 1.076 m

Now, speed of sound = frequency × wavelength
= 340 × 1.076 m/s
= 365.84 m/s