Question

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 material is

• A. 2 sin A
• B. 2 cos A
• C. $cos\frac{A}{2}$
• D. tan A

Answer 1

The correct option is B 2 cos A


It is clear from the figure that i = 2A and r = A
Thus, by using Snell's law
Sin 2A = $\mu$ sin A
or 2 cos A = $\mu$