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Light Reflection and Refraction
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20/08/2021 1:29 pm
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An object is placed 20 cm from (a) a converging lens, and (b) a diverging lens, of focal length 15 cm. Calculate the image position and magnification in each case.
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20/08/2021 1:34 pm
u = -20 cm
(a) f = 15 cm (for converging lens)
\(\frac{1}{v}\) - \(\frac{1}{u}\) = \(\frac{1}{f}\)
\(\frac{1}{v}\) - \(\frac{1}{-20}\) = \(\frac{1}{15}\)
\(\frac{1}{v}\) - \(\frac{1}{15}\) - \(\frac{1}{20}\)
\(\frac{1}{v}\) = \(\frac{1}{60}\)
v = 60 cm
m = \(\frac{v}{u}\) = \(\frac{60}{-20}\)
= -3
(b) f = -15 cm (for diverging lens)
\(\frac{1}{v}\) - \(\frac{1}{u}\) = \(\frac{1}{f}\)
\(\frac{1}{v}\) - \(\frac{1}{-20}\) = \(\frac{1}{-15}\)
\(\frac{1}{v}\) = -\(\frac{1}{15}\) - \(\frac{1}{20}\)
\(\frac{1}{v}\) = \(\frac{-7}{60}\)
v = -8.57 cm
m = \(\frac{-v}{u}\) = \(\frac{-8.57}{-20}\)
= +0.42