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Out of the two lenses, one… (Class 10 Science 2025, Q25a)

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ScienceCBSE Class 10 · Board exam 2025, set 31/2/1 · 2 marks · Very short answer

CBSE Class 10 Science 2025: question 25(a)

Set in the CBSE Class 10 board exam of 2025, paper 31/2/1, section B, question 25(a), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q25(a) · 2 marks · Very short answerLight – Reflection and Refraction

Out of the two lenses, one concave and the other convex, state which one will diverge a parallel beam of light falling on it. Draw a ray diagram to show the principal focus of the lens.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/2/1.

Hints

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

Hint 1

Which lens is thinner in the middle than at the edges?

Hint 2

For a diverging lens, the refracted rays only appear to come from a point. Draw dotted lines backwards to find it.

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 concave lens diverges (spreads out) a parallel beam of light falling on it.

    1 mark

  2. Ray diagram (describe/draw): Draw a concave lens with optical centre O on the principal axis. Draw two rays parallel to the principal axis striking the lens. After refraction they spread outwards (arrows pointing away from the axis). Extend the refracted rays backwards with dotted lines. They meet at a point F on the principal axis on the same side as the incident light. Label F as the principal focus.

    1 mark

Answer: Concave lens; the refracted rays, when produced backwards, appear to meet at the principal focus F on the side of the incident light.

Where the marks are

  • Names concave lens as the diverging lens (1 mark)
  • Correct ray diagram: parallel rays diverge, dotted back-extensions meet at F, which is labelled (1 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 31/2/1: 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.