Question

10c(iii) A compound microscope consists of an objective lens of focal length 3.0 cm and eyepiece lens of focal length 6.0 cm placed 20.0 cm apart. The final image is formed at infinity. How far is the object from the objective lens?

Accepted Answer

For the final image to form at infinity, the image formed by the objective lens must lie at the focal point of the eyepiece lens. This means the image distance for the objective lens, v₀ = 20 − 6 = 14 cm.
Using the lens formula, 1/f₀ = 1/u₀ + 1/v₀ → 1/3 = 1/u₀ + 1/14 → 1/u₀ = 1/3 − 1/14 = 11/42 → u₀ = 42/11 ≈ 3.82 cm.

WAEC Physics 2025 Theory — Question 20

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