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The radii of curvature of the faces of a...

The radii of curvature of the faces of a double convex lens are 10 cm and 15 cm. If focal length is 12 cm. What is the refractive index of glass?

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`f = + 12cm , R_(1) = 10 cm , R_(2) = - 15 cm , n = ?`
`As " " (1)/(f) = (n-1)((1)/(R_(1))-(1)/(R_(2)))`
`(1)/(12)=(n-1)((1)/(10)+(1)/(15))=(n-1)xx(5)/(30)`
`(n-1) = (6)/(12)= 0.5`
n = 0.5 + 1
n = 1.5
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