Question

The focal length of a convex lense is 20 cm .What is its power ?​

Answer 1

Answer:

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.