Millionaire Mode

Focus and focal length - class-XII

Question 1 of 36

The radii of curvature of the surfaces of a double convex lens are 20 cm and 40 cm respectively, and its focal length is 20 cm. What is the refractive index of the material of the lens.? 

  1. $\dfrac{5}{2}$
  2. $\dfrac{4}{3}$
  3. $\dfrac{5}{3}$
  4. $\dfrac{4}{5}$

Prize Money

15₹7 Crores
14₹1 Crore
13₹50,00,000
12₹25,00,000
11₹12,50,000
10₹6,40,000
9₹3,20,000
8₹1,60,000
7₹80,000
6₹40,000
5₹20,000
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1₹1,000