GRE Subject Test: Physics : Interference

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).       Explanation:

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?      Explanation:

The beat from two combined sound waves is:  All GRE Subject Test: Physics Resources 