CP Workbook
Interference
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Shown below are concentric solid and dashed circles, each different in radius by 1 cm. Consider the circular pattern a top view of water waves, where the solid circles are crests and the dashed circles are troughs.
On a sheet of paper, draw two sets of concentric circles with a compass. Choose any part of the paper for your center (except the present central point). Let the circles run off the edge of the paper. (
optional diagram
)
Find where a dashed line crosses a solid line and draw a large dot at the intersection. Do this for ALL places where a solid and dashed line intersect.
With a wide felt marker, connect the dots with smooth lines. These
nodal lines
lie in regions where the waves have cancelled - where the crest of one wave overlaps the trough of another.
Look at the construction of overlapping circles on your partner's paper. His/Her diagram may have a different number of nodal lines than on your paper due to a different starting point. How does the number of nodal lines in a pattern relate to the distance between centers of circles, or sources of waves?
Refer to the following information for the next six questions.
Carefully count the number of wavelengths (same as the number of wave crests) along the following paths between the slits and the screen.
The number of wavelengths between slit A and
point a
equals
The number of wavelengths between slit B and
point a
equals
The number of wavelengths between slit A and
point b
equals
The number of wavelengths between slit B and
point b
equals
The number of wavelengths between slit A and
point c
equals
The number of wavelengths between slit B and
point c
equals
When the number of wavelengths along each path is the same or differs by one or more whole wavelengths, interference is
constructive
destructive
When the number of wavelengths differ by a half wavelength or an odd multiple of a half wavelength, interference is
constructive
destructive
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Paul G. Hewitt
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