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Light Reflection and Refraction
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20/08/2021 1:09 pm
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A concave lens of 20 cm focal length forms an image 15 cm from the lens. Compute the object distance.
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20/08/2021 1:11 pm
f = -20 cm
v = -15 cm
\(\frac{1}{v}\) - \(\frac{1}{u}\) = \(\frac{1}{f}\)
\(\frac{1}{-15}\) - \(\frac{1}{u}\) = \(\frac{1}{-20}\)
\(\frac{1}{u}\) = -\(\frac{1}{15}\) + \(\frac{1}{20}\)
\(\frac{1}{u}\) = \(\frac{-1}{60}\)
u = -60 cm
Object distance is 60 cm towards the left of the lens.