question_answer

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)  \[0{}^\circ \]

B)  \[80{}^\circ \]

C)  \[{{50}^{0}}-{{\sin }^{-1}}\left[ \frac{\sin \,{{50}^{0}}}{1.5} \right]\]

D)  \[{{50}^{0}}-{{\sin }^{-1}}\left[ \frac{\sin \,{{50}^{0}}}{1.5} \right]-{{50}^{0}}\]

Correct Answer: B

Solution :

Refractive index, \[^{a}{{\mu }_{g}}=1.5\] \[\frac{1}{\sin C}=1.5\] \[\Rightarrow \] \[C={{42}^{o}}\] 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          \[\delta =80{}^\circ \]