Two converging lenses of focal lengths 20 cm and 30 cm are separated by 5 cm in air. Find the equivalent focal length.
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Question

Two converging lenses of focal lengths 20 cm and 30 cm are separated by 5 cm in air. Find the equivalent focal length.

G1 Physics · Accepted Answer

1/F=1/f₁+1/f₂−d/(f₁f₂), giving F=13.33 cm.