The power of a lens of focal length 10 cm is

0⋅1 dioptre

1 dioptre

10 dioptre

100 dioptre

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This question was previously asked in

UPSC CDS-1 – 2023

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The power (P) of a lens is defined as the reciprocal of its focal length (f). The focal length must be expressed in meters for the power to be in dioptres (D).
Given focal length f = 10 cm.
Convert focal length to meters: f = 10 cm / 100 cm/m = 0.1 meters.
Power P = 1 / f (in meters) = 1 / 0.1 m = 10 dioptres.

Power of a lens (in dioptres) = 1 / Focal length (in meters).

A convex lens has a positive focal length and positive power, indicating that it converges light rays. A concave lens has a negative focal length and negative power, indicating that it diverges light rays. The unit dioptre is defined as m⁻¹.

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