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

Options

A. `2 sin A`
B. `2 cos A`
C. `(1)/(2) cos A`
D. ` tan A`

Answer

B

Explanation

`A=r+0` and `mu=(sini)/(sinr)`
`implies mu=(sin 2A)/(sin A)=(2 sin A cos A)/(sinA)=2 cos A`