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JAMB Physics 2008 Question 34

Question 34

Lenses and Optical Instruments

If a convex lens of focal length 12 cm is used to produce a real image four times the size of the object, how far from the lens must the object be placed?

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

Answer: B (15cm)

Explanation

Magnification 4 means v = 4u. 1/u + 1/4u = 1/12 gives 5/4u = 1/12, so u = 15 cm.