A converging lens has focal length 12 cm. An object is placed 18 cm from it. At what distance is the image formed?

Answer and explanation

Correct answer: A. 36 cm

  1. Step 1: Use the lens equation 1/f = 1/u + 1/v, so 1/v = 1/f - 1/u.
  2. Step 2: 1/v = 1/12 - 1/18, giving v = 36 cm.
Answer
36 cm.
Why not the others: '30 cm' adds the object distance and the focal length; '6 cm' subtracts the focal length from the object distance; '216 cm' multiplies instead of using the reciprocal formula.

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