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The heat produced at a point… (Class 10 Science 2024, Q25)

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ScienceCBSE Class 10 · Board exam 2024, set 31/5/1 · 2 marks · Very short answer

CBSE Class 10 Science 2024: question 25

Set in the CBSE Class 10 board exam of 2024, paper 31/5/1, section B, question 25, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q25 · 2 marks · Very short answerLight – Reflection and Refraction

The heat produced at a point due to concentration of sunlight by a convex lens burns a paper.

  1. (a)

    Explain why it happens.

    1 mark
  2. (b)

    Name the term (in the context of the lens used) given to the point at which the paper starts burning. What does the bright spot formed on the paper represent?

    1 mark

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/5/1.

Hints

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

Hint 1

Rays from the Sun reach the lens almost parallel. What does a convex lens do to parallel rays?

Hint 2

Parallel rays meet at a special point of the lens. The spot of light there is an image of the source, so decide whether it is real or virtual.

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. (a) A convex lens is a converging lens. It brings the parallel rays of sunlight together at one point, so the light energy is concentrated there. The heat produced raises the temperature of the paper at that point and it catches fire.

    1 mark

  2. (b) The point is the principal focus of the convex lens.

    ½ mark

  3. The bright spot is the real image of the Sun formed by the lens.

    ½ mark

Answer: (a) The lens converges sunlight to a point, concentrating heat that burns the paper. (b) Principal focus; the bright spot is the real image of the Sun.

Where the marks are

  • Explains that the convex lens converges sunlight to a point, producing enough heat to burn the paper (1 mark)
  • Names the point as the principal focus (½ mark)
  • States that the bright spot is the real image of the Sun (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 paper2024 board paper, set 31/5/1: 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.