Question

In the figure, if a parallel beam of white light is incident on the plane of the slits, then the distance of the nearest white spot on the screen from $O$ is [assume $d<<D,\lambda <<d$]

• A. $0$
• B. $d/2$
• C. $d/3$
• D. $d/6$

Answer 1

The correct option is D $d/6$

The central bright white fringe wold be located at midway between the two slits at point O' as shown in figure.

Distance between O and O' $=\frac{2d}{3}-\frac{d}{2}=\frac{d}{6}$