State whether convex lens has a real focus or a virtual focus.

How could you find the focal length of a convex lens rapidly but approximately?

With the help of a labeled diagram explain how a convex lens converges a beam of parallel light rays.

List some things that convex lens and concave mirror have in common.

With the help of a labeled diagram, explain how a concave lens diverges a beam of parallel light rays.

Mark the principal axis, optical centre, principal focus and focal length of the concave lens on the diagram.