Combination of two lenses, f₁ = 20 cm convex and f₂ = -25 cm concave, in contact. Equivalent power:
A9 D
B5 - 4 = 1 D
C2 D
D1 D
Answer & Solution
Correct answer: B. 5 - 4 = 1 D
P₁ = 1/0.20 = 5 D, P₂ = 1/(-0.25) = -4 D. P = 5 + (-4) = 1 D. f = 1 m = 100 cm convex (positive).
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