CBSE 2025 · Region 2 · Set 1 · Q19 · 2 marks
Two concave lenses A and B, each of focal length $\displaystyle 8.0$ cm are arranged coaxially $\displaystyle 16$ cm apart as shown in figure. An object $\displaystyle P$ is placed at a distance of $\displaystyle 4.0$ cm from A. Find the position and nature of the final image formed.
A B
A BMarking-scheme solution
For the first lens:
$\displaystyle \frac{1}{v_{1}}-\frac{1}{u_{1}}=\frac{1}{f_{1}}$
$\displaystyle \frac{1}{v_{1}}+\frac{1}{4}=-\frac{1}{8}$
$\displaystyle v_{1}=-\frac{8}{3} \mathrm{~cm}$
For the second lens:
$\displaystyle u_{2}=-16-\frac{8}{3}=-\frac{56}{3} \mathrm{~cm}$
$\displaystyle \frac{1}{v_{2}}-\left(-\frac{3}{56}\right)=-\frac{1}{8}$
$\displaystyle v_{2}=-5.6 \mathrm{~cm}$
Image is virtual.
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CBSE Class 12 Physics past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.