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Calculate the power of a lens system with f₁ = 80 cm and f₂ = -50 cm.

1. P = 1.25 D
2. P = -0.75 D
3. P = 2 D
4. P = -2 D

Correct answer: P = -2 D

Solution

The power of a lens system is given by P = P₁ + P₂, where P₁ = 100/f₁ and P₂ = 100/f₂ (f in cm). For f₁ = 80 cm, P₁ = 100/80 = 1.25 D. For f₂ = -50 cm, P₂ = 100/(-50) = -2 D. Thus, P = 1.25 - 2 = -0.75 D.

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