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JAMB Physics 1988 Question 30

Question 30

Lenses and Optical Instruments

To obtain a magnification of 2.5, how far should an object be placed from the pole of a thin converging lens of focal length 0.20 m?

  1. A.0.13 m
  2. B.0.25 m
  3. C.0.28 m
  4. D.0.50 m.
Show the answer and explanation

Answer: C (0.28 m)

Explanation

For a real image v = 2.5u. 1/u + 1/(2.5u) = 1/0.2 gives 3.5/(2.5u) = 5, so u = 0.28 m.