Question

what is meant by power of a lens? write its SI unit. a student use a lens of focal length 40 cm and another of - 20 CM. write the nature and power of each lens

Answer 1

The degree of convergence or divergence of light rays that can be achieved by a lens is expressed in terms of its power. The S.I unit is dioptre.when f=40 then p=100/f in cm so p=2.5D and when f=-20cm then , p=-5D the nature of first one is convex lens and second one is concave lens.

Answer 2

the reciprocal of focal length of its ability of the length to Ben the Ray of the light falling on it the SI unit is diopter
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