Give the usual name for the following :

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

Refractive indices of four media A, B, C and Dare given below:

In which of these four media is the speed of light (i) maximum, and (ii) minimum ?

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

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

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?