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JAMB Physics 1981 Question 40

Question 40

Lenses and Optical Instruments

An object placed on the principle axis of a convex lens of focal length 10 cm, produces a real image of double magnification. The image distance from the lens is

  1. A.30 cm
  2. B.25 cm
  3. C.20 cm
  4. D.15 cm
  5. E.10 cm
Show the answer and explanation

Answer: A (30 cm)

Explanation

v = 2u. Then 1/u + 1/(2u) = 1/10, so 3/(2u) = 1/10, u = 15 cm and v = 30 cm.