Question

Two coherent light sources $P$ and $Q$ each of wavelength $\lambda$ are separated by a distance $3\lambda$ as shown. The maximum number of minima formed on line $AB$ which runs from $-\infty$ to $+\infty$ is:

(correct answer + 1, wrong answer - 0.25)

• A. $2$
• B. $4$
• C. $6$
• D. $8$

Answer 1

The correct option is C $6$

There can be three minima from central point to $\infty$ corresponding to $\frac{\lambda }{2},\frac{3\lambda }{2},\frac{5\lambda }{2}$ path differences.
$\therefore$ Total number of minima $=2n_{\text{max}}=6$