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

Aim

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

Apparatus

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.

Description

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.