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. $Si{n}^{-1}\left(\frac{Sin50^{\circ }}{1.5}\right)-50^{\circ }$
• B. $50^{\circ }-Si{n}^{-1}\left(\frac{Sin50^{\circ }}{1.5}\right)$
• 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 $\delta =80^{\circ }$