The focal length of a concave lens is 0.5 m. The power of the lens is

  1. A. +0.5 D
  2. B. -0.5 D
  3. C. +2.0 D
  4. D. -2.0 D

Correct Answer: D. -2.0 D

Explanation

The power of a lens is \( P = \frac{1}{f} \). For a concave lens, focal length is negative (\( f = -0.5 \) m), hence \( P = -2.0 \) D.

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