alleryA lens of focal length one metre has a power of:
AOne dioptre
BTen dioptre
CTwo dioptre
DSix dioptre
Answer & Solution
Correct answer: A. One dioptre
1. Power is the reciprocal of the focal length in metres.
2. A lens of focal length 1 metre is one dioptre.
3. So the correct answer is one dioptre.
_Source: syllabus Physics Part II, Ch 9 'Ray Optics and Optical Instruments'_
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