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Science · 2024 · 4 marks
CBSE 2024 · Region 5 · Set 1 · Q39
A highly polished surface such as a mirror reflects most of the light falling on it. In our daily life we use two types of mirrors - plane and spherical. The reflecting surface of a spherical mirrors may be curved inwards or outwards. In concave mirrors, reflection takes place from the inner surface, while in convex mirrors reflection takes place from the outer surface.(a)Define the principal axis of a concave mirror.(b)A ray of light is incident on a concave mirror, parallel to its principal axis. If this ray after reflection from the mirror passes through the principal axis from a point at a distance of $\displaystyle 10$ cm from the pole of the mirror, find the radius of curvature of the mirror.(c)An object is placed at a distance of $\displaystyle 10$ cm from the pole of a convex mirror of focal length $\displaystyle 15$ cm. Find the position of the image.(ii)A mirror forms a virtual, erect and diminished image of an object. Identify the type of this mirror. Draw a ray diagram to show the image formation in this case.
A highly polished surface such as a mirror reflects most of the light falling on it. In our daily life we use two types of mirrors - plane and spherical. The reflecting surface of a spherical mirrors may be curved inwards or outwards. In concave mirrors, reflection takes place from the inner surface, while in convex mirrors reflection takes place from the outer surface.
(a)
Define the principal axis of a concave mirror.
(b)
A ray of light is incident on a concave mirror, parallel to its principal axis. If this ray after reflection from the mirror passes through the principal axis from a point at a distance of $\displaystyle 10$ cm from the pole of the mirror, find the radius of curvature of the mirror.
(c)
An object is placed at a distance of $\displaystyle 10$ cm from the pole of a convex mirror of focal length $\displaystyle 15$ cm. Find the position of the image.
(ii)
A mirror forms a virtual, erect and diminished image of an object. Identify the type of this mirror. Draw a ray diagram to show the image formation in this case.
Marking-scheme solution
(a) It is straight line passing through the pole and centre of curvature of a concave mirror.
(b) Radius of curvature , \(\displaystyle \mathrm{R}=20 \mathrm{~cm}\)
(i) \(\displaystyle \mathrm{u}=-10 \mathrm{~cm}, \mathrm{f}=+15 \mathrm{~cm}\)
\[\frac{1}{f}=\frac{1}{v}+\frac{1}{u}
\]
\[\begin{aligned}
\frac{1}{v}=\frac{1}{f}-\frac{1}{u}=\frac{1}{15} & -\frac{1}{-10} \\
\frac{1}{v} & =\frac{1}{6} \\
& \Rightarrow \mathrm{v}=+6 \mathrm{~cm}
\end{aligned}
\]OR
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CBSE Class 10 Science past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.