Chapter 31, Problem 29A

When Thomas Young performed his interference experiment, monochromatic light passed through a single narrow opening before it reached the double openings. Explain why this made the fringes clear. (Hint: What would be the result if light reaching the double openings came from several different directions?)

To determine

To explain: The reason why the given situation made the fringes clear.

Explanation of Solution

Introduction:

The superposition of two or more light waves occupying the equal space can be defined as interference of light. Hence, a pattern of interference is formed within which the amplitudes of waves may be increased, decreased or cancel. The bright fringes occur when the reflected waves arrive in phase while the dark fringes occur when the reflected waves arrive out of phase.

If the light reaching the double openings came from several different directions, then the light passing through the double openings will be part of the same wave front. Hence, the light so passed is coherent in nature. Clearly, they show the constructive interference as they are in phase.

Conclusion:

Hence, the light passed through a single narrow opening before it reached the double openings made the fringes clear.