PASCO WA-9899 Ripple Tank System - Manual (Page 29)

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M o d e l N o . W A - 9 8 9 9 D o p p l e r E f f e c t D e m o n s t r a t i o n
29
Doppler Effect Demonstration
The Doppler effect occurs when a wave source moves relative to an observer in such
a way that the distance between the wave source and the observer changes. If the dis-
tance between the wave source and the observer decreases, the wavelength becomes
shorter. If the distance between the wave source and the observer increases, the wave-
length becomes longer.
The Doppler effect can be demonstrated using
the Ripple Tank System. Arrange the ripple
generator and ripple tank as for the previous
experiments. Mount the light source on its rod
and connect the light source to the generator.
Put a standard dipper into one of the ripple
arms of the ripple generator. Turn on the gen-
erator. Start with the ripple generator’s default
frequency of 20Hz. Set the amplitude to about
half-maximum and the light source to
‘STROBE’. See the figure.
By moving the ripple generator at a constant
speed, the Doppler phenomenon can be
observed as shown in the illustration. It will
require some experimenting to determine the
right speed to use for a given frequency.
One way to move the ripple generator is to simply pivot the gen-
erator on its support rod.To do this, grip the rod with one hand
just below the generator’s rod clamp. Slightly loosen the rod
clamp and use your thumb to support the clamp so that the gener-
ator stays at the same vertical position on the rod. Use the other
hand to rotate the generator one way and then the other. Wave-
lengths in front of the moving dipper will decrease, and wave-
lengths behind the moving dipper will increase.
Direction of motion
Figure: Doppler Demonstration