Power of a lens can be ______.
I. Positive
II. Negative
III. Zero

Correct option is A

The correct answer is (a) I, II, and III.
The power of a lens can be positive, negative, or zero, depending on its type and focal length:
1. Positive Power: Convex lenses (converging lenses) have a positive focal length, resulting in positive power. They bring parallel rays of light to a focus, hence the positive sign.
2. Negative Power: Concave lenses (diverging lenses) have a negative focal length, resulting in negative power. They cause parallel rays of light to spread out, hence the negative sign.
3. Zero Power: In certain situations, such as a plano lens (flat lens with no curvature on one side), the lens may effectively have zero power because it neither converges nor diverges light.
The power PPP of a lens is given by the formula P=1/fP = 1/fP=1/f, where fff is the focal length in meters. Depending on the focal length, power can take on positive, negative, or zero values.
Information Booster: ● Power of a lens is measured in diopters (D), with focal length in meters. ● Convex lenses have positive power and are used for focusing light (e.g., in magnifying glasses). ● Concave lenses have negative power and are used for diverging light (e.g., in corrective lenses for myopia). ● Zero power indicates no bending of light, as seen in flat or plano lenses. ● The sign of the power indicates the lens's effect on light rays (convergence or divergence).