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25. 1 dioptre is- a) power of a lens whose focal length is 100 m, b) power of a lens whose focal length is 100 cm, c)power of a lens whose focal length is 1 ft, d) power of an engine. |
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Answer» Adioptre(uk), ordiopter(us), is a unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal lengthmeasured in metres (that is,1/metres). It is thus a unit of reciprocal length.1 dioptre is SI unit of the power of a lens whose focal length is 1 metre. It is denoted by the letter D. Thus 1D = 1 m-1. Simply, when focal length ‘ f ‘ is expressed in metres, then, power is expressed in dioptres. The power of a convex lens is positive and that of a concave lens is negative. |
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