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JAMB Physics 1985 Question 30

Question 30

Light and Reflection

An object is placed 15 cm in front of a concave mirror of radius 40 cm. The image formed is

  1. A.virtual and 60 cm behind the mirror
  2. B.real and 60 cm in front of the mirror
  3. C.virtual and at infinity
  4. D.real and at infinity
  5. E.virtual and 40 cm from the mirror.
Show the answer and explanation

Answer: A (virtual and 60 cm behind the mirror)

Explanation

f = 20 cm and the object is inside f, so the image is virtual. 1/v = 1/20 − 1/15 = −1/60, so it is 60 cm behind the mirror.