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Light Reflection and Refraction
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24/08/2021 11:47 am
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An object of height 4.25 mm is placed at a distance of 10 cm from a convex lens of power +5 D.
Find (i) focal length of the lens, and (ii) size of the image.
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24/08/2021 11:53 am
h = 4.25 mm = 42.5 cm
u = -10 cm
P = +5D
(i) P = \(\frac{1}{f}\)
f = \(\frac{1}{P}\) = \(\frac{1}{5}\)
= 0.2 m = 20 cm
(ii) \(\frac{1}{f}\) = \(\frac{1}{v}\) - \(\frac{1}{u}\)
\(\frac{1}{v}\) = \(\frac{1}{f}\) + \(\frac{1}{u}\)
= \(\frac{1}{20}\) + \(\frac{1}{-10}\)
= \(\frac{-1}{20}\)
v = -20 cm
m = \(\frac{h'}{h}\) = \(\frac{v}{u}\)
\(\frac{h'}{42.5}\) = \(\frac{-20}{-10}\)
h' = 85 cm = 8.5 mm