School of Physics Lecture Demonstration Manual

Wg-2 Beats Using Two Signal Generators: Phase and Group Velocity

Published: Wednesday 15 March 2006 - Updated: Thursday 31 March 2011

Aim

To demonstrate the phenomenon of beats and illustrate the difference between phase and group velocity.

Apparatus

Diagrams

Click on pictures to enlarge.

Beats Diagram 1

Beats Diagram 2

Videos

Beats

Description

Two signal generators are fed to two channels of the C.R.O. Both generators are fed into the third channel via decoupling resistors. The C.R.O. triggers off channel one only and this waveform appears stationary on the screen. The second generator is set to a slightly different frequency and this waveform will move to the right or left of the screen depending on it having a higher or lower frequency. On the third channel the beat frequency envelope is clearly seen, together with the relationship between the group (envelope) and the phase (wave) velocity.

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