question_answer

Angle of prism is A and its one surface is silvered. Light rays falling at an angle of incidence 2A on first surface return back through the same path after suffering reflection at second silvered surface. Refractive index of the material of prism is                                                               [AIIMS 1995]

A)            2 sin A                                     

B)            2 cos A

C)            \[\frac{1}{2}\cos A\]         

D)            \[\tan A\]

Correct Answer: B

Solution :

                   \[A=r+0\] and \[\mu =\frac{\sin i}{\sin r}\] \[\Rightarrow \mu =\frac{\sin 2A}{\sin A}\]                    \[=\frac{2\sin A\cos A}{\sin A}=2\cos A\]