CBSE 2025 · Region 1 · Set 3 · Q21 · 2 marks
An object is placed at a distance of $\displaystyle 10$ cm in front of a concave mirror of focal length $\displaystyle 15$ cm. Use mirror formula to determine the position of the image formed by this mirror.
Marking-scheme solution
Here \(\displaystyle \mathrm{u}=-10 \mathrm{~cm} ; \mathrm{f}=-15 \mathrm{~cm}\);
\(\displaystyle \frac{1}{f}=\frac{1}{v}+\frac{1}{u}\)
\(\displaystyle \frac{1}{-15}=\frac{1}{v}+\frac{1}{-10}\)
\(\displaystyle \frac{1}{v}=\frac{1}{-15}+\frac{1}{10}\)
\(\displaystyle \mathrm{v}=+30 \mathrm{~cm}\)
Position of image is $\displaystyle 30$ cm from the mirror
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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.