Question

Renu's Grandfather was reading news paper using spectacles with a lens of Power 4D. Find the focal length of the lens.​

Answer 1

Answer:

Explanation:

Let the focal length of the lens = f and the power of the lens  = P

Here power = 4D

Therefore $Focal-length = f = \frac{1}{Power} = \frac{1}{P} = \frac{1}{4}meter = 0.25 m = 0.25*100 cm= 25cm$

Focal length of the lens = + 25 cm