Question

What do you mean by the power of a lens? What is the power of a lens with a focal length $–5cm$?

Answer 1

1. The power of the lens describes its capability to converge or diverge a ray of light incident on it.
2. The larger the power of a lens, the greater its capacity to refract the light that passes through it.
3. The power of a convex lens is positive while for a concave lens it is negative.
4. The expression for power of lens is,

$P=\frac{1}{f}$, where f is the focal length is in metres.

Numerical:

STEP 1: Given data

GIven data:

The power of the lens is $P=–5cm$

STEP 2:Finding the focal length

$P=\frac{1}{f}$

$P=\frac{100}{-5cm}$

$P=–20D$

Hence, the power of the lens is $P=–20D$