Question

what is the power of lens ? write the sl unite of power of lens and write the equation showing the relation between power of lens and the focal length​

Answer 1

Answer:

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Explanation:

Power of lens is defined as the reciprocal of the focal length of the lens expressed in meter. 

SI unit of power is Dioptre denoted by D.

Focal length of first lens  f1=40 cm=0.4 m

Since the focal length is positive, so it is a convex lens.

Power of lens  P1=f11=0.41=2.5 D

Focal length of second lens  f2=−20 cm=−0.2 m

Since the focal length is negative, so it is a concave lens.

Power of lens  P2=f21=−0.21=−5 D