Question

14. Two lenses of power 2.5 D and 1.5 D are joined
together. The focal length of the new lens
formed is
(A) 25 cm
(B) 100 cm
(C) 500
(D) 60 cm
- cm
3​

Answer 1

Answer:

P1 = - 2.5 D , P2 = + 1.5 D

Power of Combination ,

P = P1 + P2 = - 2.5 + 1.5 = 1.0 D

Focal length of combination , 

f = 1/p = - 1/1.0 m = 100