alleryThe focal length of a concave lens is taken to be:
APositive
BNegative
CZero
DImaginary
Answer & Solution
Correct answer: B. Negative
1. Concave lens has a virtual focus on the same side as the object.
2. By sign convention, focal length on the incoming-light side is negative.
3. So a concave lens has negative focal length.
4. A convex lens has positive focal length.
_Source: Selina Concise Physics ICSE Class 10, Ch 5 'Refraction through a Lens' (aplustopper.com extract)_
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