Question

Which among the following is not a physical quantity?

• A. Object distances
• B. Image distance
• C. Radius of curvature
• D. Centre of curvature

Answer 1

The Correct Option is D

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