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(i) A student wishes to… (Class 10 Science 2025, Q36b)

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ScienceCBSE Class 10 · Board exam 2025, set 31/3/1 · 5 marks · Long answer

CBSE Class 10 Science 2025: question 36(b)

Set in the CBSE Class 10 board exam of 2025, paper 31/3/1, section D, question 36(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q36(b) · 5 marks · Long answerLight – Reflection and Refraction

(i) A student wishes to study the image formation by a concave mirror using candle flame as object. State the type of the image formed by the mirror and mention the change in the image formed, if any, that he observes when the candle flame is gradually moved away from the pole of the mirror. Draw a ray diagram to show the image formation when the object distance is nearly equal to the radius of curvature of the mirror.

(ii) A convex mirror used for rear-view on an automobile has a focal length of 3.0 m. If a bus is located at 6.0 m from this mirror, use mirror formula to find the position of the image of the bus as seen in the mirror.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/3/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Recall how the image of a concave mirror changes as the object moves from C towards infinity.

Hint 2

Two convenient rays: one parallel to the axis, and one through F.

Hint 3

For a convex mirror f is positive; use 1/v + 1/u = 1/f with u = −6.00 m.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. (i) Type of image:

    • When the candle is beyond F, the image is real and inverted.
    • When the candle is between P and F, the image is virtual and erect.
    1 mark

  2. Change observed: As the candle is moved gradually away from the pole, the real image moves closer towards F and becomes smaller (diminished).

    1 mark

  3. Ray diagram (object at C): Draw the concave mirror with its principal axis, and mark P, F and C.

    • Place the candle AB at C.
    • Draw a ray from A parallel to the axis; after reflection it passes through F.
    • Draw a ray from A through F; after reflection it travels parallel to the axis.
    • The two reflected rays meet below the axis at A′. The image A′B′ is at C: real, inverted and of the same size as the object.
    • Put arrows on all rays.
    1 mark

  4. (ii) For a convex mirror, m and m.

    Mirror formula: , so

    1 mark

  5. , so m

    ½ mark

  6. The image is 2.0 m behind the mirror. It is virtual, erect and diminished.

    ½ mark

Answer: (i) Real and inverted (object beyond F) or virtual and erect (object between P and F); the image becomes smaller as the candle moves away; with the object at C, the image is at C, real, inverted and same size. (ii) v = +2.0 m, i.e. 2.0 m behind the mirror.

Where the marks are

  • States the type of image (real, inverted / virtual, erect) (1 mark)
  • States the image diminishes as the object moves away (1 mark)
  • Correct ray diagram for object at C (1 mark)
  • Sign convention and mirror formula with substitution (1 mark)
  • Correct calculation (½ mark)
  • v = +2.0 m, behind the mirror (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Light – Reflection and Refraction, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 31/3/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.