Converging or diverging ability of a lens or mirror is called

One of the necessary condition for total internal reflection to take place is

( $$\mathrm{i}=$$ angle of incidence, $$\mathrm{i}_{\mathrm{c}}=$$ critical angle)

A double convex lens of focal length '$$F$$' is cut into two equal parts along the vertical axis. The focal length of each part will be

The size of the real image produced by a convex lens of focal length $$F$$ is '$$m$$' times the size of the object. The image distance from the lens is