Question

A ray of light is travelling from glass to air. (refractive index of glass = 1.5). The angle of incidence is 50?. The deviation of the ray is

• A. $o^0$
• B. ${80}^0$
• C. ${50}^0-{\sin }^{-1}\left[\frac{\sin {50}^0}{1.5}\right]$
• D. ${\sin }^{-1}\left[\frac{sin{50}^0}{1.5}\right]-{50}^0$

Answer 1

Answer: (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 $\delta =80{}^{\circ }$