ray optics Questions

A biconvex lens has radii of curvature, $20\text{cm}$ 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 $\sqrt{3}$, 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 $1.5\times 10^8\text{m/s}$ and $2.0\times 10^8\text{m/s}$, respectively. The critical angle for a ray of light for these two media is: