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According to the sign convention, the focal length of a concave mirror is taken as
Apositive
Bnegative
Cinfinite
Dunity
Answer & Solution
Correct answer: B. negative
1. Distances are measured from the pole; those along the incident light are positive, opposite ones negative.
2. A concave mirror focus lies in front, on the incident-light side, i.e. the negative direction.
3. So its focal length is taken as negative.
_Source: AP/TS SCERT Class 10 Physical Science, "Reflection of Light at Curved Surfaces"_
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