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A point object is placed at a distance of 12 cm from a convex lens on its principal axis. Its image is formed on the other side of the lens at a distance of 18 cm from the lens. Find the focal length of the lens. |
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Answer» Using formula \(\frac 1v - \frac 1u = \frac1f\) \(\frac1V - \frac1{(-12)} = \frac1{18}\) \(\frac1V = \frac1{18} - \frac1{12}\) \(\frac1{V} = \frac{2- 3}{36}\) \(\frac1V = \frac{-1}{36}\) \(V = 36 cm\) Thus radius of curvature as \(V - d = R\) \(36 - 18 = R\) \(R = 18\) Focal length, f = \(\frac R2 = \frac{18}2 = 9 cm\). |
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