A lens has a power of +2.0 Dioptre. Which one of the following stateme

A lens has a power of +2.0 Dioptre. Which one of the following statements about the lens is true ?

[amp_mcq option1=”The lens is concave and has a focal length of 0.5 metre” option2=”The lens is convex and has a focal length of 2.0 metre” option3=”The lens is convex and has a focal length of 0.5 metre” option4=”The lens is concave and has a focal length of 2.0 metre” correct=”option3″]

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UPSC NDA-2 – 2020

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The correct answer is (C) The lens is convex and has a focal length of 0.5 metre.

The power of a lens (P) is the reciprocal of its focal length (f) when the focal length is measured in meters. The formula is P = 1/f. Given the power P = +2.0 Dioptre, the focal length f = 1/P = 1/2.0 = 0.5 meters. A positive power indicates a converging lens, which is a convex lens.

Concave lenses have negative power and diverge light. Convex lenses have positive power and converge light (for real objects). The unit of power is Dioptre (D), where 1 D = 1 m⁻¹.

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