JEE Main 2026 Apr 4 Shift 2, Physics Q16: Thin Lens and Mirrors

JEE Main2026Apr 4, Shift 2Physics

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

Solution

Lensmaker's equation, with $R_{1} = R$ and $R_{2} = - R$ (equiconvex):

$\frac{1}{f} = (n - 1) (\frac{1}{R _{1}} - \frac{1}{R _{2}}) = (1.4 - 1) (\frac{1}{R} - \frac{1}{- R}) = 0.4 \cdot \frac{2}{R} = \frac{0.8}{R}$ .

$∴ \frac{f}{R} = \frac{1}{0.8} = 1.25$ .

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JEE Main 2026 Apr 4 Shift 2, Physics Q16: Thin Lens and Mirrors

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