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 $