Question

power of a lens is 2.5D what is it's focal lenght

Answer 1

Power = 2.5D
We know, P = 1/f
∴ 2.5 = 1/f
⇒ f = 1/2.5
⇒f = 2/5 or 0.4 m

So the focal length is 0.4 m or 2/5 m.

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