Question 1:
Define 1 dioptre of power of a lens.
Answer:
Power of lens is defined as the reciprocal of its focal length. If P is the power of a
lens of focal length F in metres, then
The S.I. unit of power of a lens is Dioptre. It is denoted by D.
1 dioptre is defined as the power of a lens of focal length 1 metre.
∴1 D = 1 m−1
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