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 specifically designed to measure the radius of curvature of a spherical surface and the thickness of small objects. Here's how it relates to the options provided in the question: 

1. Radius of curvature of concave surface: A spherometer can be used to measure the radius of curvature of concave surfaces. It is one of the primary purposes of this instrument. The spherometer is placed on the surface, and the curvature is calculated based on the depression of the central screw relative to the outer legs.
2. Specific rotation of liquids: Specific rotation is a property of chiral compounds in solution, typically measured using a polarimeter, not a spherometer. Therefore, a spherometer cannot be used to measure this physical quantity.
3. Thickness of thin plates: By determining the difference in height between two surfaces (one where the object is present and one where it is absent), a spherometer can measure the thickness of thin plates effectively.
4. Radius of curvature of convex surface: Similar to concave surfaces, a spherometer can also measure the radius of curvature of convex surfaces. The technique remains largely the same, relying on the displacement of the central screw to signify the curvature.

Thus, specific rotation of liquids is the physical quantity that cannot be measured using a spherometer. The other options describe measurements that fall within the capabilities of a spherometer, which is primarily used for determining curvatures and thin thicknesses.

Correct Answer: Specific rotation of liquids

Answer 2

A spherometer is an instrument used primarily to measure the curvature of spherical surfaces (both concave and convex) and the thickness of thin plates. It cannot measure properties of liquids, such as specific rotation, which is a measure of the optical activity of a substance in solution.
So, the correct answer is option 2.