Question

From a point light source S, a beam of light with diverging angle $\alpha$ is produced. The light is allowed to fall symmetrically on a parallel sided glass slab of thickness ‘$t$’ and refractive index ‘$n$’. The diverging angle of the emergent beam is :

• A. Zero
• B. $\alpha$
• C. $si{n}^{-1}\left(\frac{1}{n}\right)$
• D. $2si{n}^{-1}\left(\frac{1}{n}\right)$

Answer 1

The correct option is B $\alpha$

The angle of deviation will remain same as seen from the figure.
The refracted ray on the first interface has angle r and will become the incident ray on the second interface. Hence, the refracted ray at second interface will have angle of refraction equal to $\frac{\alpha }{2}$.. The angle of divergence remains $\alpha$ only.

Hence Referring to the ray diagram we can conclude that divergent angle of the emergent beam is $\alpha$.