Question

Power of plane mirror in dioptre is

Answer 1

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A dioptre (British spelling) or diopter(American spelling) is a unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres. (1 dioptre = 1 m-1.)

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Answer 2

The focal length of a plane mirror is infinity. Power is the reciprocal of focal length.

P = 1/f   D       (D is dioptre)

P = (1/∞) = 0 D