MCQ Detailed View

In physics and optics, the dioptre (D) is the unit used to measure the optical power of a lens or curved mirror. Optical power is the ability of a lens to bend (refract) light. It is defined mathematically as the reciprocal of the focal length in meters:

P=1fP = \frac{1}{f}P=f1

where P is the power in dioptres and f is the focal length in meters.

For example, a lens with a focal length of 1 meter has a power of +1 dioptre, while a lens with a focal length of 0.5 meters has a power of +2 dioptres. Positive dioptre values represent converging (convex) lenses, whereas negative values represent diverging (concave) lenses.

The unit dioptre is widely used in optometry and ophthalmology to prescribe corrective lenses for vision problems such as myopia (short-sightedness), hyperopia (long-sightedness), and astigmatism. For instance, if an eye doctor prescribes glasses with a power of -2.0 D, it means the patient requires a concave lens with a focal length of -0.5 meters to correct their vision.

Now, let’s analyze the incorrect options:

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  Luminous intensity → This is measured in candela (cd), not dioptres.

  
  


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  Power (general energy per time) → Measured in watt (W).

  
  


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  Distance of heavenly bodies → Measured in light-years, parsecs, or astronomical units (AU), not dioptres.

  
  

Therefore, the correct answer is Optical Power, making dioptre a key concept in physics, particularly in optics and vision science.