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Science — CBSE Class 10 board question

Q1. [5]
Answer the following:
  1. (i) Draw a ray diagram to show the path of the reflected ray in each of the following cases : A ray of light incident on a convex mirror (1) parallel to its principal axis, and (2) is directed towards its principal focus
  2. (ii) A 1.5 cm tall candle flame is placed perpendicular to the principal axis of a concave mirror of focal length 12 cm. If the distance of the flame from the pole of the mirror is 18 cm, use mirror formula to determine the position and size of the image formed.
Previously asked in CBSE board exam
2024 31/3/1 Q36(b)
Generated by claude-sonnet-4-6 · 2026-06-15 06:52 · grounding rag
Model Answer

(i) Ray diagrams for a convex mirror:

Case 1: A ray parallel to the principal axis, after reflection, appears to diverge from the principal focus F (behind the mirror).

Case 2: A ray directed towards the principal focus F, after reflection, emerges parallel to the principal axis.

(Diagrams should show the convex mirror with centre of curvature C and focus F behind the mirror, with reflected rays diverging as described.)

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(ii) Given: h = 1.5 cm, f = −12 cm (concave), u = −18 cm

Using mirror formula:
$$\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$$
$$\frac{1}{v} = \frac{1}{f} - \frac{1}{u} = \frac{1}{-12} - \frac{1}{-18} = \frac{-3+2}{36} = \frac{-1}{36}$$
$$v = -36 \text{ cm}$$

The image is formed 36 cm in front of the mirror (real and inverted).

Magnification:
$$m = -\frac{v}{u} = -\frac{-36}{-18} = -2$$

Size of image: $h' = m \times h = -2 \times 1.5 = -3$ cm

The image is 3 cm tall, real, inverted, and magnified.

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Explanation
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