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For a lens with R₁ = 60 cm, R₂ = ∞, and μ = 1.6, calculate the focal length.

1. f = 10 cm
2. f = 100 cm
3. f = 20 cm
4. f = 50 cm

Correct answer: f = 20 cm

Solution

Using the lens maker's formula, 1/f = (μ - 1)(1/R₁ - 1/R₂), and substituting R₁ = 60 cm, R₂ = ∞, and μ = 1.6, we get 1/f = (1.6 - 1)(1/60 - 0). Solving, f = 20 cm.

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