School of Physics Lecture Demonstration Manual

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

Published: Tuesday 14 March 2006 - Updated: Wednesday 30 March 2011


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



Click on pictures to enlarge.

Ultrasound 1

Ultrasound 4

Speed of Sound Diagram


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.

Safety notes

Electrical safety 


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