JEE Main · 2026 · 04 Apr 2026 · Shift 2 · Geometrical Optics

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A convex lens is made from glass material having refractive index of 1.4 with same radius of curvature on both sides. The ratio of its focal length and radius of curvature is ______ .

(A)0.5
(B)2.5
(C)0.8
(D)1.25✓ Correct

Answer: (D)

Solution

For a symmetric biconvex lens

R_{1} = R

and

R_{2} = - R

. The lens-maker's relation gives

\frac{1}{f} = (n - 1) (\frac{1}{R} - \frac{1}{- R}) = (1.4 - 1) \frac{2}{R} = \frac{0.8}{R}

. Hence

\frac{f}{R} = \frac{1}{0.8} = 1.25

JEE Main · 2026 · 04 Apr 2026 · Shift 2 · Single correct option

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