Question

A compound lens is made of 2 lenses in contact having powers +12.5 D and -2.5D. Find focal length and power of combination

Answer 1

p=p1+p1
=12.5-2.5
=10D

f=1/p

f=1/10
=.1

Answer 2

focal length of first lens(F1) = 1/D
= 1/12.5
= 10/125
=0.08cm
Focal length of second lens(F2) =1/D
= 1/-2.5
= -10/25
=-0.4