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The eye can be regarded as a single refracting surface. The radius of curvature of this surface is equal to that of cornea (7.8 mm). This surface separates two media of refractive indices 1 and 1.34. Calculate the distance from the refracting surface at which a parallel beam of light will come to focus

Asked in JEE Main 10th Jan 2nd Shift 2019 · Single spherical surface

• (1) 4.0 cm
• (2) 1 cm
• (3) 3.1 cm
• (4) 2 cm

Step-by-step solution

Why the other options are wrong

• (1) Rounds up a mis-computed (1.34×0.78)/(0.26).
• (2) Multiplies R by μ₂ (1.34×0.78≈1.0 cm) and forgets to divide by μ₂-μ₁.
• (4) Uses R/(μ₂-μ₁)=(0.78)/(0.34)≈2.3 cm, dropping the factor μ₂, and rounds.

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