Velocity of Sound

In this experiment, we use a pair of 40 KHz  piezo electric crystals to study the propagation of sound in air. We apply a 5 volts pulse, 13 microseconds wide, to the transmitter piezo to make it undergo mechanical vibrations to generate a 40 KHz sound wave. The receiver piezo kept at a distance converts this sound waves back into electrical signals. These are amplified by two inverting amplifiers in series, each with a gain of 100, and displayed. By changing the distance between the crystals we can observe the change in time sound takes to travel from one to the other, as shown in the screen shot below.

       The amplified waveform can also be applied to a Digital Input of Phoenix to measure the time more accurately, The schematic for this is shown below.
One can do this experiment from the GUI or using the python program piezo.py. The time measurement at each distance should be repeated several times and a histogram should be plotted to find the mean value. Values differ from the mean value by around 25 microseconds should be ignored since there are caused by adjacent raising edges. Measure the time for several values of the distance and plot the graph. Slope of the graph dS/dt, taken from any linear portion, gives the velocity of sound.