Question

A converging lens has a focal length of 50 cm. The power of this lens is (a) +0.2D
(b) −2.0D
(c) +2.0D
(d) −0.2D

Answer 1

Power of the lens is 2 D

Explanation:

Given ,

Focal length of a converging lens = 50 cm

                                                         = $50\times 10^{-2}$ M

= 0.5 m

Power of the lens (P) = ?

We know that,

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

P =$\frac{1}{0.5}$

P =  2 D

Power of the lens is 2 D

Answer 2

Answer is Option (C)

Explanation:

Given,

• Let the Power of Lens be P D

And the Focal length of Lens, F = 50 cm or $\frac {50}{100}$

= 0.5 m

We know that the Power of Lens is inversely proportional to the focal length of the lens.

or Power = $\frac {1}{Focal Length}$

Power = $\frac {1}{0.5}$

Power = $\frac {10}{5}$

Power = 2

or Power = + 2 D