Question

In Young’s double slit experiment the two slits are d distance apart. Interference pattern is observed on a screen at a distance D from the slits. A dark fringe is observed on the screen directly opposite to one of the slits. The wavelength of the light is

• A. $\frac{D^2}{2d}$
• B. $\frac{d^2}{2D}$
• C. $\frac{D^2}{d}$
• D. $\frac{d^2}{D}$

Answer 1

The correct option is D $\frac{d^2}{D}$

$(n-\frac{1}{2})\frac{D\lambda }{d}=\frac{d}{2}$
$\lambda =\frac{d^2}{(2n-1)D}$
$\lambda =\frac{d^2}{D}$ for n=1.