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Power of a Lens: Measuring Lens Strength and Prescription Explained

Power of a lens is a measure of how strongly the lens converges or diverges light. It is the reciprocal of focal length in meters. A lens with power of +2

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TL;DR: Power of a lens is a measure of how strongly the lens converges or diverges light. It is the reciprocal of focal length in meters. A lens with power o…

Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated Jul 23, 2026

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Power of a Lens: Measuring Lens Strength and Prescription: Power of a lens is a measure of how strongly the lens converges or diverges light. It is the reciprocal of focal length in meters. A lens with power of +2

Power of a Lens: Measuring Lens Strength and Prescription Explained Simply

Power of a lens is a measure of how strongly the lens converges or diverges light. It is the reciprocal of focal length in meters. A lens with power of +2 This is a key physics concept for 10.

Frequently Asked Questions

What is the power of a lens?

The power of a lens is its ability to converge or diverge light. It is the reciprocal of the focal length measured in metres: P = 1/f.

What is the unit of power of a lens?

The SI unit is the dioptre (D), where 1 D = 1 m⁻¹. A lens with a focal length of 1 metre has a power of 1 dioptre.

Is the power of a convex lens positive or negative?

A convex (converging) lens has positive power; a concave (diverging) lens has negative power.

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