Question

A ray of light is 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. $Sin^{-1} \Big( \frac {Sin 50^\circ}{1.5} \Big)-50^\circ$
• B. $50^{\circ}-Sin^{-1} \Big( \frac {Sin 50^{\circ}}{1.5} \Big)$
• C. $80^\circ$
• D. $0^\circ$

Answer 1

Answer: (C)

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 $(\delta)=180^{\circ}-\left(50^{\circ}+50^{\circ}\right)$
(from the-figure)
or $\delta=80^{\circ}$