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Unilorin Post-UTME Physics 2024 (Model questions) Question 5

Question 5

Lenses and Optical Instruments

A convex lens forms a real image twice the size of the object. What is the object distance from the lens in terms of the focal length (f)?

  1. A.f
  2. B.1.5f
  3. C.2f
  4. D.3f
Show the answer and explanation

Answer: B (1.5f)

Explanation

Magnification 2 means v = 2u. Then 1/u + 1/(2u) = 1/f, so 3/(2u) = 1/f and u = 1.5f.