Question

What happens to the interference pattern if the two slits in a Young's experiment, are illuminated by two independent sources (such as two sodium lamps $S$ and $S^{\prime }$) as shown in figure?

• A. Two sets of interference fringes overlap.
• B. No fringes are observed.
• C. The intensity of the bright fringes is doubled.
• D. The intensity of the bright fringes becomes four times.

Answer 1

The correct option is B No fringes are observed.

Two physically different sources can never be coherent sources. So, no fringes are observed, as we need two coherent sources to obtain interference pattern, in Young's double slit experiment

Hence, $\left(B\right)$ is the correct answer.

$\begin{array}{c}\text{Why this question?}\\ \text{Note :- Fringes are observed only when the two sources are coherent.}\end{array}$