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Light Reflection and Refraction
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18/08/2021 2:00 pm
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An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens.
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18/08/2021 2:03 pm
\(h_2\) = 50 cm
\(h_1\) = -20 cm(Real image)
v = 10 cm
m = \(\frac{v}{u}\) = \(\frac{h_2}{h_1}\)
\(\frac{10}{u}\) = \(\frac{-20}{50}\)
u = -25 cm
\(\frac{1}{v}\) - \(\frac{1}{u}\) = \(\frac{1}{f}\)
\(\frac{1}{10}\) - \(\frac{1}{-25}\) = \(\frac{1}{f}\)
f = \(\frac{50}{7}\) = 7.14 cm