Problem 5.83

Monochromatic light passes through an orifice in a screen $S c$ (Fig. 5.17 ) and being reflected from a thin transparent plate $P$ produces fringes of equal inclination on the screen. The thickness of the plate is equal to $d,$ the distance between the plate and the screen is $l$, the radii of the $i \mathrm{th}$ and $k$ th dark rings are $r_{i}$ and $r_{k} .$ Find the wavelength of light taking into account that $r_{i, k} \ll l$.