CBSE 2025 · Region 5 · Set 2 · Q26 · 3 marks
An air bubble is trapped at point $\displaystyle \mathrm{P}(\mathrm{CP}=1 \cdot 75 \mathrm{~cm})$ in a spherical glass ball ( $\displaystyle \mathrm{n}=1 \cdot 5$ ) of radius $\displaystyle 7$ cm as shown in the figure. Find the nature and position of the image when viewed from side B . Show the image formation by drawing a ray diagram.
Marking-scheme solution
For light going from denser to rarer medium:
$\displaystyle \frac{n_{2}}{-u}+\frac{n_{1}}{v}=\frac{n_{1}-n_{2}}{R}$
$\displaystyle \frac{1.5}{8.75}+\frac{1}{v}=\frac{(1-1.5)}{-7}$
$\displaystyle \frac{1}{v}=\frac{0.5}{7}-\frac{1.5}{8.75}$
$\displaystyle =\frac{-1}{10}$
$\displaystyle v=-10 \mathrm{~cm}$
Nature of the 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.