Question

What is meant by power of a lens? Write its SI unit. A student uses a lens of focal length 40 cm and another of –20 cm. Write the nature and power of each lens.

Answer 1

Answer

Power of lens is the ability to converge or diverge light rays passing through it. It is the reciprocal of the focal length in metres.

P = 1/

SI unit of power is Dioptre.

Power of 1st lens 1 = 100/1 = 100/40 cm = +2.5 D

Nature: Converging lens / Convex lens

Power of 2nd lens 2 = 100/2 = 100/−20 cm = -5 D

Nature: Diverging lens / Concave lens

Answer 2

Explanation:

power of lenses means that the convergence or divergence of a light rays.

In simple language, it means the reciprocal of focal length.SI unit is diopter