Question

Unit of power of lens is:
A) Meters
B) hp
C) Dioptre
D) cms

Answer 1

The definition of the power of a lens is the ability of a lens to converge or diverge a beam of light rays falling on a lens. We know that the convex lenses are the converging lens and the concave lenses are the diverging lens.

Formula Used:
We will be using the relation of $D = \dfrac{1}{f}$.

Complete step by step answer:
Unit of measurement of the power on optical curves or lenses is known as Dioptre. It is represented by the letter (D).
The power of a lens is also defined as the reciprocal of its focal length which is measured in meters.
Also, the light ray will bend to get the more effective power because of that lens of shorter focal length. The S.I unit of length is meter.
The Converging lenses have positive power values because they have the positive focal lengths.
The Diverging lenses have negative focal lengths so they have a negative power value.
Hence the Convex lens has positive power and the Concave lens has negative power. Power of a plane glass plate is zero.
$D = \dfrac{1}{f}$
Where, D is the power in Dioptre and $f$ is the focal length in meters
A convex lens converges the light rays towards the principal axis and the concave lens diverges the light rays away from the principal axis.
The unit of the reciprocal length is (${\text{1Dioptre = 1}}{{\text{m}}^{{\text{ - 1}}}}$).
In the CGS system, the unit of power lens is ${\text{centimeter}}{{\text{s}}^{{\text{ - 1}}}}$.

Hence the correct option is C.

Note: A lens of small focal length has large power of converging or diverging a parallel beam of light. The power of combinations of lenses in contact with each other is equal to the sum of individual power of each lens.