Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Speed of Sound by Air Resonance


To adjust a column of vibrating air to get resonance with a tuning fork of known frequency is a standard text book method to measure speed of sound in air at room temperature. In this experiment we suggest another arrangement for this measurement using the same basic principle.}


a speaker, a frequency generator, water in a bucket, a cylindrical tube (= 30 cm).


  1. Take water in the bucket and dip the cylindrical tube in it vertical. Hold it with one with most of the tube in air.
  2. Ask your friend to connect the speaker to the output of the frequency generator and put the speaker close to the open and of the tube. Make the frequency about 1~kHz. Keep the amplitude low so that surrounding the speaker is barely audible.
  3. Lower the tube and the speaker gradually and listen the sound. Adjust for the position where the sound intensity is maximum.
  4. Switch off the function generator. Measure the length of the tube above the water surface. This should be approximately \(\lambda/4\).
  5. Calculate the speed of sound in lab air from \(v=\nu\lambda\).