A beam of monochromatic light passes through a pile of `N = 5` identical plane-parallel glass plates each of thickness `l = 0.50 cm`. The coefficient of reflection at each surface of the plates is `rho = 0.050`. The ratio of the intensity of light transmitted through the pile of plates to the intensity of incident light is `tau = 0.55` Neglecting the secondary reflections of light, find the absorption coefficient of the given glass.

Explanation

On each surfcae we pick up a factor `(1 - rho)` from reflection and a factor `e^(-chil)` due to absorption in each plane.
Thus `tau = (1 - rho)^(2N) e^(chiNl)`
Thus `chi = (1)/(Nl) In ((1 - rho)^(2N))/(tau) = 0.034 cm^(-1)`