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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 ______.

Options

  1. A0.5
  2. B2.5
  3. C0.8
  4. D1.25

Correct answer

D. 1.25

Step-by-step solution

Using the lens maker's formula: 1 f = ( - 1) ( 1 R₁ - 1 R₂ ) For an equiconvex lens, R₁ = R and R₂ = -R . Given = 1.4 : 1 f = (1.4 - 1) ( 1 R - 1 -R ) 1 f = 0.4 2 R 1 f = 0.8 R f R = 1 0.8 = 1.25 Answer: 1.25

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