Abstract:  An ultrasonic interference device is built in this paper, in which two independent and adjustable wave sources are introduced. One is a fixed wave source and the other is a parallel moving one. With this device, the wavelength of ultrasonic waves can be measured based on nearly complete destructive interference of waves, and then the speed of sound can be measured accurately. This method can be regarded as an improvement in the measuring methods of sound speed in the current experimental course of college physics. And this device can also be used to demonstrate the phenomenon of beats caused by the superposition of two waves of slightly different frequencies.

Key words: destructive interference, measurement of sound speed, beats