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Light Reflection and Refraction
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20/08/2021 12:59 pm
Topic starter
A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.
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20/08/2021 1:02 pm
f = -15 cm
v = -10 cm
\(\frac{1}{v}\) - \(\frac{1}{u}\) = \(\frac{1}{f}\)
\(\frac{1}{-10}\) - \(\frac{1}{u}\) = \(\frac{1}{-15}\)
\(\frac{1}{u}\) = -\(\frac{1}{10}\) + \(\frac{1}{15}\)
\(\frac{1}{u}\) = \(\frac{-2}{60}\)
u = -30 cm
Object is at 30 cm from the concave lens (on left side).
Here, OB = 30 cm
OF = 15 cm
OB' = 10 cm