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NDA 2 2025 GAT, question 51

Topic: Physics

Q51

The focal length of a concave lens is 0.5 m0.5\text{ m}. The power of the lens is

  1. (a) +0.5 D+0.5\text{ D}
  2. (b) −0.5 D-0.5\text{ D}
  3. (c) +2.0 D+2.0\text{ D}
  4. (d) −2.0 D-2.0\text{ D}Correct answer

Solution.

Answer: (d) −2.0 D-2.0\text{ D}

  1. A concave lens has negative focal length: f=−0.5 m.
  2. Lens power P=1/f=−2 dioptres.
  3. The metre must be used when calculating power in dioptres.