Q15DQ - University Physics with Modern Physics

Question

Interference can occur in thin films. Why is it important that the films be thin? Why don’t you get these effects with a relatively thick film? Where should you put the dividing line between “thin” and “thick”? Explain your reasoning.

Step-by-Step Solution

Answer

 In the first case of thin films, the sources are coherent but in the second case, waves do not exhibit coherence.

Step 1: (a) Concept of interference.

It is a phenomenon where one light wave superposes over another coherent light wave and this superposition leads to a redistribution of the intensity of light rays at different points.

Step 2: (b) Explanation of the argument.

The condition for obtaining any type of interference pattern is that the sources are coherent. The meaning of coherent sources is that they maintain the same phase difference. In the thin films, the reflected waves come from the same burst but for thick films, there is an additional path difference. This breaks the coherence and the interference patterns are not obtained.