Question

a concave lens of focal length 25cm and a concave lens of focal length 10cm are placed in close contact with each other calculate the lens power of this combination

Answer 1

Hey!!

This is your answer.

Given :

According to sign convention of lenses, focal length of Concave lens is written in negative and that of convex Lens is written as positive.

Focal length of Concave lens = 25 cm = -0.25 m
So, power = 1/f (in m) = 1/-0.25 = -4 D

And focal length of second Concave lens = 10. cm = -0.10 m
Power = 1/-0.10 = -10. D

Now, Power of combination = P1 + P2 + ....... Pn
= -4 - 10 = -14 D.

hope It Helps