All GRE Subject Test: Physics Resources
Example Questions
Example Question #1 : Interference
A double slit experiment is set up with the following parameters: two slits are a separated by a distance . A beam of light with wavelength
shines through the two slits, and is projected onto a screen a distance
from the slits. What is the distance on the screen between the central band and the next band on either side? (This distance is marked '
' on the figure).
The condition for constructive interference with double slit diffraction is given by:
Where is 0, 1, 2, ...
Solving for the angle and using the small angle approximation, we get;
The distance in the diagram can be related to the other quantities by simple geometry:
Again, with the help of the small angle approximation. Setting the two thetas equal to each other and solving for , we get:
For the central band, , so the
position is also zero. The next band,
, yields a distance of:
Example Question #2 : Interference
Two waves with frequencies: are combined. What is the frequency of the resulting beat?
The beat from two combined sound waves is:
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All GRE Subject Test: Physics Resources
