Velocity of Sound

A voltage waveform of known frequency is applied to piezo disc. A microphone is placed in front of it. The phase difference between the driving waveform and the microphone output voltage are plotted. The distance by which the microphone is moved to generate a phase difference of 180 degree (half wavelength) is measured by adjusting the distance between the source and the microphone.

In phase and out of phase conditions, after changing the distance by around 4.3 cm