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Science · 2023 · 5 marks
CBSE 2023 · Region 2 · Set 3 · Q36
(a) Draw a ray diagram for showing the convergence of a parallel beam of light by a concave mirror and mark the positions of pole and the centre of…
(a)
Draw a ray diagram for showing the convergence of a parallel beam of light by a concave mirror and mark the positions of pole and the centre of curvature in it.
(b)
An object $\displaystyle 4$ cm in size is placed at $\displaystyle 25$ cm in front of a concave mirror of focal length $\displaystyle 15$ cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image ? Find the nature and size of the image.
(c)
List any two uses of a concave mirror.
Marking-scheme solution
(a) (i)
(P, F, C should be labelled correctly.)
(P, F, C should be labelled correctly.)(b) \(\displaystyle \frac{\mathbf{1}}{\mathbf{v}}+\frac{\mathbf{1}}{\mathbf{u}}=\frac{\mathbf{1}}{\mathbf{f}}\)
\[\Rightarrow \frac{1}{v}=\frac{1}{f}-\frac{1}{u}=\frac{1}{-15}-\frac{1}{-25}=-\frac{1}{15}+\frac{1}{25}=\frac{-2}{75}
\]
or \(\displaystyle \mathrm{v}=-37 \cdot 5 \mathrm{~cm}\)
The screen should be placed at \(\displaystyle 37 \cdot 5 \mathrm{~cm}\) from the mirror. The image is real and inverted.
Also, magnification, \(\displaystyle \mathrm{m}=\frac{\mathrm{h}^{\prime}}{\mathrm{h}}=-\frac{\mathrm{v}}{\mathrm{u}}\)
\[\mathrm{h}^{\prime}-\frac{\mathrm{vh}}{\mathrm{u}}=-\frac{(-37 \cdot 5 \mathrm{~cm})(+4 \cdot 0 \mathrm{~cm})}{(-25 \cdot 0 \mathrm{~cm})}
\]
Height of the image \(\displaystyle =\mathrm{h}^{\prime}=-6.0 \mathrm{~cm}\). The image is inverted and enlarged.
(c)
Torches, search lights
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CBSE Class 10 Science past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.