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Physics · 2022 · 3 marks
Ray Optics and Optical InstrumentsRefraction at Spherical Surfaces and by Lenses3 marksApplyshort answer
CBSE 2022 · Region 2 · Set 3 · Q6
An equiconvex lens forms a two times enlarged real image when an object is kept 16 cm from it. The lens is cut into two identical plano-convex…
An equiconvex lens forms a two times enlarged real image when an object is kept $\displaystyle 16$ cm from it. The lens is cut into two identical plano-convex lenses. If the object is again kept $\displaystyle 16$ cm in front of one of these lenses, then find the nature and position of the image formed.
Marking-scheme solution
Finding the position of the image Nature
$\displaystyle \frac{1}{f}=\frac{1}{\mathrm{v}}-\frac{1}{\mathrm{u}}$
$\displaystyle \frac{1}{f}=\frac{1}{32}+\frac{1}{16}=\frac{1+2}{32}=\frac{3}{32}$
$\displaystyle f=\frac{32}{3} c m$
When lens is cut into two equal halves the new focal length $\displaystyle =f^{\prime}=2 f=\frac{64}{3} \mathrm{~cm}$
$\displaystyle \frac{1}{f^{\prime}}=\frac{1}{\mathrm{v}}-\frac{1}{\mathrm{u}} \Rightarrow \frac{3}{64}=\frac{1}{v}+\frac{1}{16}$
$\displaystyle \mathrm{v}=-64 \mathrm{~cm}$
Image formed is virtual \
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CBSE Class 12 Physics past-paper question from the 2022 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.