Question

A compound lens is made up of two thin lenses having power + 12.5 D
and – 2.5 D. Find the focal length and power of the combination

Answer 1

Given :
P1=+12.5D
P2=-2.5D
Power of combination P=P1+P2
=12.5-2.5
=10D

As we know that P=1/f
f=1/p
=1/10=0.1m 
=0.1 x100 = 10cm 
∴Total power is 10 D and focal length is 10cm

Answer 2

hey mate !!!


total focal length of combination = > 10 cm .


hope it helps!!!


thanks