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Science · 2025 · 2 marks
CBSE 2025 · Region 1 · Set 1 · Q24
An object is placed at a distance of 60 cm from a concave lens of focal length 30 cm. Use lens formula to find the position of the image formed in…
An object is placed at a distance of $\displaystyle 60$ cm from a concave lens of focal length $\displaystyle 30$ cm. Use lens formula to find the position of the image formed in this case.
Marking-scheme solution
\[\begin{aligned}
& \mathrm{u}=-60 \mathrm{~cm} \quad \mathrm{f}=-30 \mathrm{~cm} \\
& \frac{1}{f}=\frac{1}{v}-\frac{1}{u} \\
& \frac{1}{-30 \mathrm{~cm}}=\frac{1}{v}-\frac{1}{-60 \mathrm{~cm}} \\
& \frac{1}{v}=\frac{1}{-30}-\frac{1}{60} \\
& \frac{-3}{60 \mathrm{~cm}}=\frac{1}{v} \Rightarrow \mathrm{~V}=-20 \mathrm{~cm}
\end{aligned}
\] Position of image is $\displaystyle 20$ cm from a concave lens.
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