The focal length of a spherical mirror is related to its radius of curvature R by:
A. f = 2R
B. f = R
C. f = R/2
D. f = R²
Answer: Option C
Solution (By JKSSB Mock Tests)
For spherical mirrors (concave or convex), focal length f = R/2, where R is radius of curvature. This holds under paraxial approximation (small angles). Derivation uses geometry of reflection and small-angle approximations. Memory tip: 'Mirror: f = R/2; Lens: 1/f = (n-1)(1/R₁ - 1/R₂)'. This fundamental relation is frequently tested in optics sections of competitive exams. Always note sign conventions: f negative for convex mirrors, positive for concave; R follows same sign as f.
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