Problem 5.75

A plane light wave with wavelength $\lambda=0.70 \mu \mathrm{m}$ falls normally on the base of a biprism made of glass $(n=1.520)$ with refracting angle $\theta=$ $=5.0^{\circ} .$ Behind the biprism (Fig. 5.15) there is a plane-parallel plate, with the space between them filled up with benzene $\left(n^{\prime}=1.500\right)$. Find the width of a fringe on the screen $S c$ placed behind this system.