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InterviewSolution
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Double - convex lenses are to be manufactured from a glass of refractive index 1.55, with both faces of the same radius of curvature. What is the radius of cavature required if the focal length is to be 20 cm? |
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Answer» Solution :Here, `n=1.55, f=+20 cm` and `|R_(1)| =|R_(2)| = R` SAY) MOREOVER, as per sign convention, for a CONVEX lens `R_(1)` is +ve and `R_(2)` is `-ve` hence, `1/f =(n-1) [1/R -1/(-R)] =(n-1) (1/R + 1/R) =(2(n-1))/R` `rArr R =2(n-1) f = 2 xx (1.55 -1) xx 20 = 2 xx 0.55 xx 20 = 22 cm` |
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