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A concavo-convex lens has an index of refraction 1.5 and the radii of curvature of its surface are 10 cm and 20 cm. The concave surface is upwards and it is filled with an oil of refractive index 1.6. Calculate the focal length of the oil-glass combination. |
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Answer» Solution :for theglass lens`(1)/(F)= (mu-1) [(1)/(R_1)-(1)/(R_2)]` Here`R_1= 10 cm, R_2= 20 cm andmu = 1.5` `(1)/(f_1) = (1.5 -1) [(1)/(10 cm) - (1)/(20 cm)]=(1)/(40 cm )` FORTHE oillens ` (1)/(f_2) =(mu-1) [(1)/(R_1) - (1)/(R_2)]` Here ` R_1= 20 cmR_2= ooandmu =1.6 ` ` (1)/(f )= (1.6-1)[(1)/(20 cm) - (1)/(OO)] = (3)/(100 cm)` Forthe OIL- glasscombination `(1)/(f)=(1)/(f_1) +(1)/(f_2)= (1)/(40 cm ) +(3)/( 100 cm ) =(11)/(200 cm )` `thereforef=18.2cm ` |
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