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Light Reflection and Refraction
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24/08/2021 11:41 am
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An object of height 4 cm is placed at a distance of 15 cm in front of a concave lens of power, -10 dioptres. Find the size of the image.
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24/08/2021 11:46 am
h = 4 cm
u = -15 cm
P = -10D
P = \(\frac{1}{f}\)
f = \(\frac{1}{P}\)
= \(\frac{1}{-10}\)
= -0.1 m
= -10 cm
Using lens formula,
\(\frac{1}{f}\) = \(\frac{1}{v}\) - \(\frac{1}{u}\)
\(\frac{1}{v}\) = \(\frac{1}{f}\) + \(\frac{1}{u}\)
= \(\frac{1}{-10}\) + \(\frac{1}{-15}\)
= \(\frac{-5}{30}\)
v = -6 cm
Magnification, m = \(\frac{h'}{h}\) = \(\frac{v}{u}\)
\(\frac{h'}{4}\) = \(\frac{-6}{-15}\)
h' = 1.6 cm