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JAMB Physics 1991 Question 29

Question 29

Lenses and Optical Instruments

Which of the following correctly describes the image of an object, 4 cm from a diverging lens of focal length −12 cm?

  1. A.The image is virtual, 3 cm in front of the lens
  2. B.The image is real, 6 cm behind the lens
  3. C.The image is virtual, 6 cm in front of the lens
  4. D.The image is real, 3 cm in front of the lens.
Show the answer and explanation

Answer: A (The image is virtual, 3 cm in front of the lens)

Explanation

1/v = 1/f − 1/u = −1/12 − 1/4 = −1/3, so v = −3 cm: a virtual image 3 cm from the lens on the object's side.