Physics - Wave Optics Question with Solution | TestHub

Concept: In biprism experiment, location of the nth dark band is the location of the nth dark fringe given by, $y_n=(2n-1)\frac{\lambda D}{2d}$ Given, slit width $=\mathrm{d}$, and ${\mathrm{y}}_4=\frac{\mathrm{d}}{2}$ $\begin{array}{rl}& {\mathrm{y}}_4=\left(\frac{7\lambda \mathrm{D}}{2\mathrm{d}}\right)=\left(\frac{\mathrm{d}}{2}\right)\\ & \therefore \lambda =\left(\frac{{\mathrm{d}}^2}{7\mathrm{D}}\right)\end{array}$ Option (D) is correct.