PASCO WA-9899 Ripple Tank System - Manual (Page 16)

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R i p p l e T a n k S y s t e m E x p e r i m e n t 2 : R e f r a c t i o n
16
Part 1: Refraction Using a Straight Barrier
Procedure
1. Arrange the trapezoidal refractor in the water in the middle of the tank so the
rectangular end of the refractor is parallel to the plane wave dipper and about 5
cm from the dipper (see Figure 2.2).
2. Add just enough water to the tank so that the refractor is evenly covered by less
than 1 mm of water.
3. Turn on the ripple generator and
the light source. Set the light
source to ‘STROBE’. Set the rip-
ple generator frequency to 15 Hz
or less. Set the amplitude to
slightly less than half of maximum
and adjust it as necessary to make
a clear pattern of plane waves.
4. On the paper below the tank, trace
the outline of the trapezoidal
refractor.
5. Place the ruler parallel to the plane
waves that are incoming to the
refractor. Sketch lines to show the
incoming wave fronts.
6. On the outline of the refractor, trace the shapes of the refracted waves to show the
bending of the refracted waves as they travel over the refractor.
7. After sketching the waves, reverse the trapezoidal refractor so that the triangular
end of the refractor points toward the plane wave dipper and repeat the proce-
dure.
8. Turn off the ripple generator and light source.
Data Analysis
1. Draw a line that is perpendicular to the incoming wave front and extend the line
to the outline of the trapezoidal refractor. This represents the incoming ray, so
draw an arrow on it pointing to the refractor.
2. At the point where the line representing the incoming ray meets the outline of the
refractor, draw a new line that is perpendicular to the wave fronts of the refracted
waves as they pass over the trapezoidal refractor.
Questions
1. What happens to the direction of the wave fronts as they move over the trapezoi-
dal refractor?
2. As the plane wave from the deep water moves through the shallower water over
the refractor, does the plane wave speed up or slow down?
Figure 2.2: Position of Trapezoidal Refractor
Tip: Adjust the frequency
as needed to make a clear
wave pattern as the waves
move over the refractor.
The lower the frequency,
the more pronounced the
refraction.