Question

4. Find the focal length of a lens of donar-20D. what type of lens in this​

Answer 1

We are given the power of lens =20D

And focal length is f = 1/P

Therefore...... Focal length is

f = 1/20

= - 0.05m or - 5 cm

Since power is negative... Focal length will be negative..... Therefore this is a concave lens.....