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The Human Eye and Colourful World
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04/12/2020 12:45 pm
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A 52-year-old near-sighted person wears eye-glass with a power of –5.5 dioptres for distance viewing. His doctor prescribes a correction of +1.5 dioptres in the near-vision section of his bifocals. This is measured relative to the main part of the lens
(i) What is the focal length of his distance-viewing part of the lens?
(ii) What is the focal length of the near-vision section of the lens?
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04/12/2020 12:48 pm
(i) Focal length of lens for distance viewing f1 = 1/P1 = 1/-5.5
= -0.182 m
= -18.2 cm
(ii) Focal length for near vision f2 = 1/P2
= 1/1.5 = 0.667 m = 66.7 cm