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

The following table gives the refractive indices of a few media:

Use this table to give an example of:

(i) a medium pair so that light speeds up when it goes from one of these medium to another.

(ii) A medium pair so that light slows down when it goes from one of these medium to another.

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 ?

Give the usual name for the following :

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

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