PASCO WA-9899 Ripple Tank System - Manual (Page 22)

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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 4 : I n t e r f e r e n c e
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Procedure: Straight Barriers
1. Place the short barrier between the two long barriers in the water to form two
openings that are 2 cm long. Put the barriers parallel to the plane wave dipper as
shown in Figure 4.2. Set the barriers about 5 cm from the plane wave dipper
2. Turn on the ripple generator and the
light source. Set the light source to
‘STROBE’. Set the frequency to 20 Hz
and the amplitude to slightly less than
half of maximum.
3. On the paper below the tank, trace the
outline of the barriers.
4. Sketch the wave fronts and the rays that
represent the waves as they spread out
and interfere after they pass through the
slits between the barriers.
5. Find and label the regions where the
waves from the two slits tend to cancel
each other and find and label the regions where the waves add together to make
waves with higher peaks.
6. Decrease the slit separation. Replace the short barrier with the mini barrier but
keep the slit width at 2 cm.
7. Vary the frequency. Keep the slip separation and slit width the same, but increase
the frequency to decrease the wavelength.
Questions
1. When the slit separation is decreased, does the spread angle of the waves increase
or decrease?
2. When the frequency increases and the wavelength decreases, does the spread
angle of the waves increase or decrease?
Setup: Two Point Sources
1. Temporarily turn off the ripple generator.
2. Remove the straight barriers from the tank and replace
the plane wave dipper in the ripple arms with two stan-
dard dippers (see Figure 4.3). Adjust the ripple generator
so that the two standard dippers barely touch the surface
of the water.
Procedure: Two Point Sources
1. Turn on the generator and return the frequency to 20 Hz.
Adjust the amplitude as needed to make a clear pattern.
2. Sketch the wave pattern formed as the wave fronts from the two point sources
interfere with each other.
Figure 4.2: Position of Barriers
Tip: Adjust the ampli-
tude to make a clear
pattern of plane waves.
Figure 4.3: Standard Dippers