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If A forms the image on the same side as the object and B on the other side of the lens for a given object placed at 20 cm from each lens, calculate the power of each lens. |
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Answer» For lens A \(\frac{h_i}{h_0}=\frac{-(-v)}{u}\) \(\frac{2}{6}=\frac{+v}{-20}\) \(v=-\frac{20}{3}\,cm\) u = - 20 cm \(v=\frac{-20}{3}\,cm\) \(\frac{1}{f}=\frac{-3}{20}+\frac{1}{20}=\frac{-20}{20}=\frac{-1}{10}\) f = - 10 cm \(P=\frac{100}{-10}=-10\,D\) For lens B \(\frac{2}{6}=\frac{-v}{-20}\) \(v=+\frac{20}{3}\,cm\) \(\frac{1}{f}=\frac{3}{20}+\frac{1}{20}=\frac{4}{20}\) \(f=\frac{20}{4}=5\,cm\) \(P=\frac{100}{5}=20\,D\) |
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