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

`n_(1) " sin 2A" = n_(2) ` sin A
`rArr n_(21) = (2 sin A cos A )/(sin A ) `
= 2 cos A.