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Using the sign convention for curved mirrors, what sign does the focal length carry for a concave mirror, and what sign for a convex mirror?
APositive for concave, negative for convex
BNegative for concave, positive for convex
CPositive for both concave and convex mirrors
DNegative for both concave and convex mirrors
Answer & Solution
Correct answer: A. Positive for concave, negative for convex
1. The sign convention states that for concave mirrors, f is positive, since converging rays form a focal point in front of the mirror.
2. For convex mirrors, f is negative, since the rays only appear to diverge from a point behind the mirror.
3. Giving both mirror types the same sign would erase the very distinction the convention is built to capture.
_Source: OpenStax Physics (CC BY 4.0), Ch 16 "Mirrors and Lenses", section 16.1 Reflection_
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