Question

A convex lens of focal length 25 cm and a concave lens of focal length 10cm
Placed closed in contact with each other calculate the power

Answer 1

we know that in a convex lens the focal length is positive and in concave lens it is negative so

in convex lens f= 25cm and

concave lens f = -10

= focal length of con vex + concave lens

=25-10 = 15cm

but power is inversely proportional to 1m of focal length so we should convert 15 cm to meters

=  0.15 m = 1/0.15

= 6.6 D = power