JEE Main 2013PhysicsRay OpticsMediumMCQ

JEE Main 2013 — Ray Optics Question with Solution

JEE Main 2013 (07 Apr)

Question

Diameter of a plano - convex lens is 6 cm and thickness at the centre is 3 mm. If the speed of light in the material of lens is 2×108 m s-1, the focal length of the lens is:

Choose an option

Show full solutionCorrect option: A
Correct answer
A30 cm

Step-by-step explanation



AB=6 cm

r=3 cm
O A 2 = O P 2 + P A 2

R 2 = R - t 2 + r 2

R 2 = R 2 + t 2 - 2 R t + r 2

2 R t = t 2 + r 2

R = t 2 + r 2 2 t = 0 · 3 2 + 3 2 2 × 0 · 3

R≈r22t=322×0·3=90·6=906=15 cm

Use 1 f = μ - 1 1 R 1 - 1 R 2

1 f = 1 . 5 - 1 1 1 5 = 1 3 0

f=30 cm

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About this question

This is a previous-year question from JEE Main 2013, covering the Ray Optics chapter of Physics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.