A diverging beam of light from a point source S having divergence angle `alpha`, falls symmetrically on a glass slab as shown in the figure. The angles of incidence of the two extreme rays are equal. If the thickness of the glass slab is t and the refractive index n, then the divergence angle of the emergent beam is

Options

A. zero
B. `alpha`
C. `sin^(-1)((1)/(n))`
D. `2sin^(-1)((1)/(n))`

Answer

b.

Explanation

The path of rays become parallel to initial direction as they emerge.
Applying Snell's law at P,`(1)/(2)n=(sinalpha//2)/(sinr)` (i)
Applying Snell's law at Q, `(1)/(2)n=(sinbeta//2)/(sinr)` (ii)
From Eqs. (i) and (ii), `alpha=beta`
Therefore, (b) is the correct answer. ltbgt