Question

You are given two lenses of equal size, concave and convex .How will you distinguish them without touching their surfaces?

Answer 1

We can distinguish between concave an covex lens by the following ways:

Concave lens

• The center portion of lens would be thin and the top and bottom part would be thick.
• As the name indicates  the lens appears like a cave from both sides
• when we pass a light through it the lens would diverge it.

Convex lens

• The center portion of this lens would be thick and the top and bottom portion would be thin.
• The convex lens is formed by combining two convex mirror so the lens would be bulging from both sides.
• When a light passes through it the lens would converge it.

Answer 2

How will you distinguish between a convex and a concave lens without touching them? We will keep the lens close to some page of a book and see the print of the book through it. If the letters of the book appear enlarged, it is a convex lens and if they appear diminished, it is concave lens.