Question

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

Answer 1

Explanation:

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. Power of combination of lenses : The focal length of the combination of two lenses placed in contact is given by the relation