Question

Identify the physical quantity that cannot be measured using a spherometer:

• A. Radius of curvature of concave surface
• B. Specific rotation of liquids
• C. Thickness of thin plates
• D. Radius of curvature of convex surface

Answer 1

The Correct Option is B

A spherometer is an instrument designed for measuring the radius of curvature of spherical surfaces and the thickness of small objects. Its applicability to the given options is as follows:

1. Radius of curvature of concave surface: A spherometer can measure the radius of curvature of concave surfaces. This is a primary function. The instrument is placed on the surface, and the curvature is calculated based on the central screw's depression relative to the outer legs.
2. Specific rotation of liquids: Specific rotation is a property of chiral compounds in solution, measured with a polarimeter, not a spherometer. A spherometer is incapable of measuring this physical quantity.
3. Thickness of thin plates: A spherometer can effectively measure the thickness of thin plates by determining the difference in height between surfaces with and without the object.
4. Radius of curvature of convex surface: A spherometer can also measure the radius of curvature of convex surfaces using a method similar to that for concave surfaces, relying on the central screw's displacement to indicate curvature.

Therefore, specific rotation of liquids is the physical quantity that cannot be measured using a spherometer. The other options represent measurements within the spherometer's capabilities, which are primarily focused on determining curvatures and thin thicknesses.

Correct Answer: Specific rotation of liquids