Question

Q. Focal length of a convex lens is 20cm . find its power?​

Answer 1

Answer:

Formulae : D = 1/f where F is the focal length and D is the power of the lens in Diopter. From the question above given the focal length is 20cm we can get the power of the lens using this formula.

Answer 2

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

Explanation:

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