Wa-6 The Speed of Sound (Using Lissajous figures)


To measure the speed of sound in air using ultrasonic transducers by the Lissajous method.


  • Ultrasonic transmitter and Receiver
  • C.R.O.
  • Signal Generator
  • 1/4 metre optical bench

Lissajous Figure 1 Lissajous Figure 2 Lissajous Figure Diagram

Speed of Sound Lissajous Method Setup.


The ultrasonic transducers used in the demonstration resonate at 26 kHz. The transmitter (marked with a red dot) is connected to the signal generator and the receiver connected initially directly to the Y input of the C.R.O. A slight adjustment of the frequency may be necessary to maximise the output signal on the C.R.O. The transmitter is now reconnected to the y input and the receiver to the x input of the C.R.O. to produce a Lissajous figure. It is best to separate the transducers to such an extent that a single line is produced.