Q. A ray of light travelling from glass to air (refractive index of glass=1.5). The angle of incidence is $50{^\circ}.$The deviation of the ray is
A) $0{^\circ}$
B) $80{^\circ}$
C) $50{^\circ}\ - \sin^{- 1}\left\lbrack \frac{\sin{50{^\circ}}}{1.5} \right\rbrack$
D) $\sin^{- 1}{\left\lbrack \frac{\sin{50{^\circ}}}{1.5} \right\rbrack - 50{^\circ}}$
Explanation
(b) Refractive index, $\ _{a}\mu_{g}\ = \ 1.5$
$\frac{1}{\sin C} = 1.5$
$\Rightarrow C = 42{^\circ}$
Critical angle for glass $= \ 42{^\circ}$
When the angle of incidence in the denser medium is greater than the critical angle, reflection takes place inside the denser medium.
Hence, a ray of light incident at $50{^\circ}$ in glass medium undergoes total internal reflection.
Deviation $(\delta)\ = \ 180{^\circ} - (50{^\circ} + 50{^\circ})$
(from the figure)
Or $\delta\ = \ 80{^\circ}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.