Question

Two thin convex lenses if power 4D and 6D are placed Co-axially at a distance of 20cm apart. Find the focal length and power of the combination of lenses

Answer 1

hey mate
p = 4+6
= 10D
f =1/p
= 1/10
=0.1
combine of lenses =0.1×20 =2cm

Answer 2

Given

P1=4D

P2 = 6D

Now P=P1+P2

P= 10D

Focal length will be f= 1/P

f = 1/10

f = 0.1m