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Light Reflection and Refraction
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18/08/2021 1:54 pm
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A lens forms a real image 3 cm high of an object 1 cm high. If the separation of object and image is 15 cm, find the focal length of the lens.
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18/08/2021 1:59 pm
\(h_2\) = -3 cm (Real image)
\(h_1\) = 1 cm
-u + v = 15 cm
m = \(\frac{v}{u}\) = \(\frac{h_2}{h_1}\)
\(\frac{15 + u}{u}\) = \(\frac{-3}{1}\)
15 + u = -3u
u = -3.75 cm
v = 15 + u = 15 + (-3.75)
= 11.25 cm
\(\frac{1}{v}\) - \(\frac{1}{u}\) = \(\frac{1}{f}\)
\(\frac{1}{11.25}\) - \(\frac{1}{-3.75}\) = \(\frac{1}{f}\)
f = 2.82 cm