A converging lens has focal length 10 cm. An object is placed 20 cm from it. At what distance is the image formed?

Answer and explanation

Correct answer: B. 20 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 = 1/10 - 1/20, giving v = 20 cm.
Answer
20 cm.
Why not the others: '30 cm' adds the object distance and the focal length; '10 cm' subtracts the focal length from the object distance; '200 cm' multiplies instead of using the reciprocal formula.

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