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A lens has a power of +2.0 Dioptre. Which one of the following statements about the lens is true?

Options

  1. AThe lens is concave and has a focal length of 0.5 metre
  2. BThe lens is convex and has a focal length of 2.0 metre
  3. CThe lens is convex and has a focal length of 0.5 metre
  4. DThe lens is concave and has a focal length of 2.0 metre

Correct answer

C. The lens is convex and has a focal length of 0.5 metre

Step-by-step solution

A dioptre, is a unit of measurement of the optical power of a lens, which is equal to the reciprocal of the focal length measured in meters (that is, 1 / f metres). It is thus a unit of reciprocal length. Hence, P =1 / f 2=1 / f f =0.5 meter. As the value is positive, it is a positive lens, that is, convex. Hence, the option (c) is true.

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