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Per NCERT, what is the sign of FOCAL LENGTH f for a CONCAVE mirror — and for a CONVEX mirror?
ABoth negative
BConcave mirror: f is NEGATIVE (focus in front); Convex mirror: f is POSITIVE (focus behind)
CBoth positive
DConcave positive, convex negative
Answer & Solution
Correct answer: B. Concave mirror: f is NEGATIVE (focus in front); Convex mirror: f is POSITIVE (focus behind)
Per NCERT §9.2.3, concave f < 0 (focus in front, on the negative side); convex f > 0 (focus behind).
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