Question

(A person uses a concave lens with a focal length of 20 cm as spectacles. What is the power of the lens?) *​

Answer 1

Answer:

similarly the power of a concave lens of focal length 20 cm is 5.0 dioptre.

Answer 2

Answer:

Power of Lens = 1/f

where f is the focal length in metres.

f = 20 cm = 0.2 m

Power P = 1/f = 1/0.2 = 10/2 = 5 D

But since this is a concave lens, it's focal length will be negative, and hence the power will also be negative.

P = (-) 5 D

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