A biconvex lens has radii of curvature, 20 cm each. If the refractive index of the material of the lens is 1.5, the power of the lens is

A light ray falls on a glass surface of refractive index $$\sqrt3$$, at an angle 60$$^\circ$$. The angle between the refracted and reflected rays would be

Two transparent media A and B are separated by a plane boundary. The speed of light in those media are 1.5 $$\times$$ 10⁸ m/s and 2.0 $$\times$$ 10⁸ m/s, respectively. The critical angle for a ray of light for these two media is