Chapter 24, Problem 22Q

To determine

To explain: The reason due to which the interference fringes are noticeable only for thin film like a soap bubble and not for a thick piece of glass.

Explanation of Solution

Introduction:

The superposition of two waves to form a resultant wave is termed as interference of light.

Various interference patterns are mixed together in case of thick film which makes it difficult to observe certain effects individually. If we consider a thickness of about 1 $\lambda$ then, the path difference of each color consists of one constructive and one destructive interference pattern. Hence, the interference fringes are noticeable for such amount of thickness.

On the other hand, when the film has greater thickness it consists of many constructive and destructive interference patterns. So, the resultant interference pattern is overlapping and much closely packed and it is difficult for the eyes to differentiate between the bright and dark fringes.

As the film gets thicker, all the colors mix together due to overlapping of patterns and hence it is impossible to see the interference patterns individually.

Conclusion:

Hence, the interference fringes are noticeable only for thin film like a soap bubble and not for a thick piece of glass.