Spherical Lenses

A physical quantity is something that can be measured and expressed numerically, often with units.

- Object distance, image distance, and radius of curvature are all measurable and have standard units (meters in SI).
- Centre of curvature, however, is a geometrical point—not a measurable physical quantity.

It refers to the center of the sphere from which the mirror or lens surface is a part.
Since it is a position or location and not a quantity with magnitude and unit, it is not a physical quantity.

The correct option is (D): Centre of curvature

Bifocal lenses are used to correct the defect of vision known as presbyopia. Presbyopia is the condition in which the eye's ability to focus on near objects decreases with age, and bifocal lenses help in correcting this by having two different optical powers, one for near and one for distant vision.

The correct option is (B): presbyopia