Teaching Physics with the Physics Suite Edward F. Redish

Representing an interference pattern

In class, a pattern was produced on the wall by putting a laser beam through two thin slits. Suppose that the width of the individual slits, a, were much less than the separation between the slits, d.

1. Given the scale of the parameters you observed in class, draw a diagram of the light that is responsible for the illumination at a particular point on the screen (right-hand wall of the lecture hall). What approximations would be useful for calculating the interference pattern produced?
2. Assuming that d >> a, sketch a picture of the pattern that would be observed. What is the angular width of the central peak? Be sure to define any terms you introduce.
3. Now suppose that we replace the slits with another set that has d = 2a. Draw a graph of the light intensity of the resulting pattern as a function of angle. Do it carefully, showing the angles at which the first two zeros occur.

Note to the instructor: For this to have the desired estimation components, the demonstration would have to have been carried out in class at some point.

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