Question

A concave lens of focal length 25 cm and a convex lens 20 cm are placed in contact with each other .What is the power of this combination ?Also calculate the focal length of the combination.

Answer 1

Explanation:

given that

f( convex lens)f1=20

f(cancave lens)f2=25

power of a convex lens p1=100/f1

=100/20=+5D

power of cancave lens p2=100/f2

=100/25=-4D

1) power of combination(p3) =p1+p2=1

2) focal length of comBination =100/p3

=100/1=100 cm