Question

the focal length of lense is ‐20 cm then the power of lens is ​

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

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Answer 2

Answer:

The power of the lens is -5D

Explanation:

Because

P=1 / foc.length( -20cm should be converted into meter because Dioptre(D)

is the power of the lens having focal length of 1 m)