A 1 cm high object is placed at a distance of 2f from a convex lens. What is the height of the image formed?

Name the lens which can concentrate sun's rays to a point and bum a hole in a piece of paper.

Give the usual name for the following :

A point inside a lens through which the light passes undeviated.

If the image formed by a convex lens is of the same size as that of the object, what is the position of the image with respect to the lens?

If an object is placed at the focus of a convex lens, where is the image formed?