Question

doctor advised to use 4d lens the focal length of lensis

Answer 1

use the formula power=1/focal length (in metre)
4=1/f
f=1/4 metre
f=0.25metre

Answer 2

Answer:

f = 25 cm

Explanation:

It is given that,

Power of the lens, P = 4 D

We need to find the focal length of the lens. The relation between the focal length and the power of a lens is given by :

$P=\dfrac{100}{f}\ cm$

or

$f=\dfrac{100}{P}\ cm$

$f=\dfrac{100}{4}\ cm$

f = 25 cm

So, the focal length of the lens is 25 cm. Hence, this is the required solution.