Chapter 10 • Question 1
Define the principal focus of a concave mirror.
Q1
Define the principal focus of a concave mirror.
Answer Revealed
Direct Answer: The principal focus of a concave mirror is the point on the principal axis where all reflected rays parallel to the principal axis converge after reflection.
Simple Explanation
The principal focus is the point where all light rays coming in parallel to the main axis of a concave mirror meet after bouncing off it.
Exam-Ready Structure
The principal focus (F) of a concave mirror is a point on the principal axis where all rays of light parallel and close to the principal axis converge (meet) after reflection from the mirror. Key points: 1. It is a real focus because the reflected rays actually pass through it. 2. It lies in front of the mirror on the principal axis. 3. For a concave mirror, the focus is between the pole (P) and the centre of curvature (C). 4. The distance from the pole to the principal focus is called the focal length (f).
Key Points
- Light rays parallel to principal axis converge at focus
- It is a real focus — rays actually pass through it
- Lies on the principal axis between pole and centre of curvature
- Distance from pole to focus is the focal length