Question
When a spherical lens is held towards the Sun and a sharp image is formed on a piece of black paper, a hole gets burnt in the black paper, after some time.
(a) Name the lens used in the above activity.
(b) What name is given to the distance between the spherical lens and the black paper?
(c) What is the relative advantage of using a black paper rather than a white paper?
Answer
a) Convex lens.
b) Focal length.
c) Black colour absorbs most of the energy falling on it, while white colour reflects most of the energy falling on it. So, black paper can burn faster than white paper.