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 mirror 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.
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It looks like sub-question (c) is incomplete — the two options (i) and (ii) were not included in your message. I'll answer (a) and (b) fully, and note the gap for (c).
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Model Answer
(a) The principal axis of a concave mirror is the straight line passing through the centre of curvature and the pole of the mirror.
(b) A ray parallel to the principal axis, after reflection from a concave mirror, passes through the focus (F). Therefore, the focal length $f = 10$ cm.
$$R = 2f = 2 \times 10 = \textbf{20 cm}$$
The radius of curvature of the mirror is 20 cm.
(c) (The options (i) and (ii) were not provided in the question. Please share them so this part can be answered.)
Source: Light – Reflection and Refraction, Spherical Mirrors
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Explanation
- For (a): Examiners expect both reference points — the pole and the centre of curvature — to be mentioned for full marks.
- For (b): The key concept is that a ray parallel to the principal axis reflects through the focus. So the given 10 cm distance is the focal length, and $R = 2f$. Show the formula and calculation clearly.
- For (c): Once you share the options, the answer will be written to the full 2-mark length. Don't leave it blank in the actual exam.