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Question 20226
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Ray Optics: Lens Maker's Formula MCQ

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Lens Maker's FormulaEasyQuestion 20226

Question

Lens maker's formula for a thin lens (refractive index n, radii R₁ and R₂) is:
  1. A
    1/f = (n−1)(1/R₁ − 1/R₂)
    Correct
  2. B
    1/f = (n+1)(1/R₁ + 1/R₂)
  3. C
    1/f = n(1/R₁ − 1/R₂)
  4. D
    1/f = (n−1)(1/R₁ + 1/R₂)

Correct answer

1/f = (n−1)(1/R₁ − 1/R₂)

Explanation

Lens maker's formula: 1/f = (n−1)[1/R₁ − 1/R₂]. R₁ = radius of first surface (positive if centre is to right), R₂ = radius of second surface. For biconvex lens: R₁ > 0, R₂ < 0 → f > 0 (converging).

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