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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.

1. 2 cm
2. 3.1 cm
3. 4.0 cm
4. 1 cm

Correct answer: 3.1 cm

Solution

For a single refracting surface with a parallel incident beam, n2/v = (n2-n1)/R, so v = n2*R/(n2-n1) = 1.34*7.8/(0.34) = 30.7 mm = 3.1 cm.

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