CBSE 2025 · Region 2 · Set 3 · Q31 · 3 marks
A convex mirror used for rear view on an automobile has a focal length of $\displaystyle 1.5$ m . If a $\displaystyle 3$ m high bus is located at $\displaystyle 6.0$ m from the mirror, use mirror formula to determine the position and size of the image of the bus as seen in the mirror.
Marking-scheme solution
Here \(\displaystyle f=+1.5 \mathrm{~m} ; \mathrm{u}=-6.0 \mathrm{~m} ; \mathrm{h}=3 \mathrm{~m}\)
\[\frac{1}{v}+\frac{1}{u}=\frac{1}{f}
\] \(\displaystyle \frac{1}{v}+\frac{1}{-6}=\frac{1}{1.5} \frac{1}{\mathrm{v}}=\frac{1}{6}+\frac{1}{1.5} \mathrm{v}=\frac{6}{5}=1.2 \mathrm{~m} \frac{\mathrm{h}^{\prime}}{\mathrm{h}}=\frac{-\mathrm{v}}{\mathrm{u}} \frac{\mathrm{h}^{\prime}}{3}=\frac{1.2}{6} \mathrm{h}^{\prime}=0.6 \mathrm{~m}\)
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CBSE Class 10 Science past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.