CBSE 2026 · Region 5 · Set 2 · Q21 · 2 marks
A point source, in air, is placed at a distance of $\displaystyle 6$ cm in front of a convex spherical surface ( $\displaystyle \mathrm{n}=1 \cdot 5$ and radius of curvature $\displaystyle =24 \mathrm{~cm}$ ). Find the position and nature of the image formed.
Marking-scheme solution
\[\begin{aligned}
& \frac{\mathrm{n}_{2}-\mathrm{n}_{1}}{R}=\frac{\mathrm{n}_{2}}{\mathrm{v}}-\frac{\mathrm{n}_{1}}{u} \\
& \frac{1.5-1.0}{24}=\frac{1.5}{\mathrm{v}}-\frac{1.0}{-6}
\end{aligned}
\]
After solving
\[\mathrm{v}=\frac{-72}{7} \approx-10.28 \mathrm{~cm}
\]
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CBSE Class 12 Physics past-paper question from the 2026board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.