The angle of prism is $$A$$ and one of its refracting surface is silvered. Light rays falling at an angle of incidence '$$2 \mathrm{A}$$' on the first surface return back through the same path after suffering reflection at the silvered surface. The refractive index of the material of the prism is

The refractive index of glass is 1.5 and that of water is 1.33 . The critical angle for a ray of light going from glass to water is

A convex lens is dipped in a liquid whose refractive index is equal to refractive index of lens material. Then its focal length will

A ray of light is incident at an angle 'I' on one face of thin prism. The ray emerges normally from the other face. Refractive index of the glass prism is '$$n$$' and angle of prism is '$$A$$'. The value of '$$\mathrm{I}$$' is