Question

The focal length of which mirror is taken as negative according to the convention of signs?

• A. Plane mirror
• B. Concave mirror
• C. Convex mirror
• D. None of these

Hint:

Remember: Concave = negative focal length, Convex = positive focal length.

Answer 1

The Correct Option is B

Step 1: Sign convention.
In mirror formula, distances measured against incident light are taken negative.
Step 2: Mirrors.
For concave mirror, focal length is on the left side (against light), hence negative.
For convex mirror, focal length is positive.
Step 3: Conclusion.
So, concave mirror has negative focal length.