Power of a Lens – Class 12 | Chapter – 9 | Physics Short Notes Series PDF for NEET & JEE
Power of a Lens: The power of a lens is a measure of its ability to bend light and is defined as the reciprocal of its focal length. The unit of power is the diopter, which is equal to the reciprocal of the focal length in meters. The power of a lens is an important parameter used in the prescription of corrective eyeglasses or contact lenses for individuals with refractive errors, such as myopia (nearsightedness) or hyperopia (farsightedness).
The power of the lens prescribed is determined by the degree of the refractive error and the distance of the lens from the eye. The power of a lens is also an important consideration in the design of optical instruments, such as cameras, telescopes, and microscopes, where it is used to determine the magnification and focus of the system.
Formula of Power of a Lens
The formula for calculating the power of a lens is:
Power (P) = 1 / focal length (f)
Where, P is the power of the lens in diopters and f is the focal length in meters.
For example, if a lens has a focal length of 0.5 meters, its power would be:
P = 1/0.5 = 2 diopters
Lenses with a higher power bend light more strongly than those with a lower power. A lens with a power of +1.0 diopters, for example, would be more powerful than one with a power of +0.5 diopters. The sign of the power (+ or -) indicates whether the lens is converging or diverging, respectively.
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