Question

For obtaining maximum contrast between the bright and dark fringes in an interference pattern, the intensities of the two light coherent sources should be

• A. large
• B. small
• C. equal
• D. in the ratio \(2:1\)

Hint:

Width of the central maximum is 2 lambda D over a.

Answer 1

The Correct Option is C

Step 1: First minimum:
The first minimum is at $a\sin\theta = \lambda$, so on the screen $y = \frac{\lambda D}{a}$ (small angle).

Step 2: Total width:
The central maximum extends from $-y$ to $+y$, a width $\frac{2\lambda D}{a}$. Setting it equal to a gives $D = \frac{a^2}{2\lambda}$ (D).

Final Answer:
$\frac{a^2}{2\lambda}$. \[ \boxed{D = \frac{a^2}{2\lambda}} \]