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The radii of curvature of the faces of a double convex lens are 10 cm and 15 cm. If focal length of the lens is 12 cm, find the refractive index of the material of the lens. |
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Answer» SOLUTION : Here it is GIVEN that `R_1 = 10 cm, R_2 = 15 cm` and `f= 12 cm`. As per sign convention followed for a CONVEX lens, f and `R_1` are +ve but `R_2` is -ve. Hence, applying lens maker.s formula `1/f =(n-1) (1/R_(1)-1/R_(2))`, we have `1/(+12) =(n-1) [1/(+10) -1/(-15)] =(n-1) (1/10 + 1/15) =(n-1) xx 1/6` `rArr (n-1) = 6/12 = 1/2` or `n=1+1/2 = 3/2 = 1.5` |
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