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An equiconvex crown glass lens has a focal length 20 cm for violet rays. Its focal length for red rays is (mu_(v)=1.5 "and" mu_(r)=1.47) |
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Answer» `20.82` CM For VIOLET rays : `(1)/(20)=(1.5-1)xx(2)/(R)` ...(i) For red rays : `(1)/(f_(r))=(1.47-1)xx(2)/(R)` ...(ii) DIVIDING (i) by (ii), we get `(1)/(f_(r))=((1.5-1)/(1.47-1))=(0.5)/(0.47)` or `f_(r)=(0.5)/(0.47)xx20=21.28` cm |
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