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The lens formula for a thin lens is:
A1/v − 1/u = 1/f
B1/v + 1/u = 1/f
Cv + u = f
Dv u = f
Answer & Solution
Correct answer: A. 1/v − 1/u = 1/f
1. The thin-lens formula: 1/v − 1/u = 1/f.
2. New Cartesian sign convention: u is taken negative for real objects (on the left).
3. Compare with mirror formula 1/v + 1/u = 1/f — sign of u differs.
_Source: NCERT Class 10 Science Ch 9 §9.3.6 Lens Formula_
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