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For a spherical mirror, the relation between focal length f and radius of curvature R is:
Af = R · 1
Bf = R / 2
Cf = R · 2
Df = R / 1
Answer & Solution
Correct answer: B. f = R / 2
1. For paraxial rays in a spherical mirror, the focus lies midway between the pole and the centre of curvature.
2. So f = R / 2.
3. Equivalently R = 2f.
_Source: NCERT Class 10 Science Ch 9 §9.2.2 Relation between f and R_
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