Question

The power off a lense issue 40 it's focal length is

Answer 1

HOPE IT HELPS YOU THANKS

I HAD TAKEN UNIT OF POWER AS DIOPTRE SO THE UNIT OF FOCAL LENGTH IS METER

Answer 2

The power of a convex lens is positive and that of a concave lens is negative. Thus a convex lens of focal length 40 cm is said to possess a power of + 2.5 dioptre. similarly the power of a concave lens of focal length 20 cm is 5.0 dioptre