Question

To find normal to a curved surface at a point, join that point and

• A. Focus (F)
• B. Pole (P)
• C. Centre of curvature (C)
• D. Any point on principal axis

Answer 1

The Correct Option is C

To solve this problem, we need to understand how to draw the normal to a curved surface (such as a mirror or lens) at a given point on its surface.

1. Understanding the Normal to a Curved Surface:
The normal at any point on a curved mirror (concave or convex) is defined as the line that passes through that point and the centre of curvature (C).

2. Why Centre of Curvature?
The centre of curvature is the center of the sphere from which the mirror surface is a part. The radius of this sphere always lies normal (perpendicular) to the surface at any point on the mirror. So, joining the point on the mirror to the centre of curvature gives the correct normal.

3. Evaluating Given Options:

• (A) Focus (F) – Incorrect; it's not used for finding the normal.
• (B) Pole (P) – Incorrect; the normal does not necessarily pass through the pole.
• (C) Centre of curvature (C) – Correct; normal is along the line joining the point and C.
• (D) Any point on principal axis – Incorrect; arbitrary points are not used for normal construction.

Final Answer:
The correct answer is (C) Centre of curvature (C).