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Light Reflection and Refraction
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17/08/2021 11:50 am
Topic starter
A lens of focal length 12 cm forms an erect image three times the size of the object. The distance between the object and image is :
(a) 8 cm
(b) 16 cm
(c) 24 cm
(d) 36 cm
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17/08/2021 11:55 am
(b) 16 cm
Explanation:
Magnification, m = \(\frac{v}{u}\)
3 = \(\frac{v}{u}\)
⇒ v = 3u
Lens formula: \(\frac{1}{v}\) - \(\frac{1}{u}\) = \(\frac{1}{f}\)
\(\frac{1}{3u}\) - \(\frac{1}{u}\) = \(\frac{1}{12}\)
\(\frac{-2}{3u}\) = \(\frac{1}{12}\)
⇒ u = -8 cm
v = 3 x -8 = -24 cm
Distance between object and image = u - v
= -8 - (-24) = -8 + 24
= 16 cm