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A ray of light after… (Class 10 Science 2025, Q25b)

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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(b)

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

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

A ray of light after refraction from a convex lens emerges parallel to its principal axis.

  1. (i)

    Draw a labelled ray diagram to show it.

    0 marks
  2. (ii)

    In this case, the incident ray before refraction from the lens passes through a point on its principal axis. Name the point.

    0 marks

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

Light paths are reversible. A ray parallel to the axis goes through the focus.

Hint 2

So which point must the incident ray pass through to come out parallel?

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) Ray diagram (describe/draw): Draw a convex lens with optical centre O. Mark foci F₁ (left) and F₂ (right) on the principal axis. Draw an incident ray from the left that passes through F₁ and strikes the lens. After refraction, draw it emerging parallel to the principal axis on the right side. Put arrows on both rays and label O, F₁ and F₂.

    1 mark

  2. (ii) The incident ray passes through the principal focus (F₁) of the convex lens. A ray through the focus becomes parallel to the principal axis after refraction.

    1 mark

Answer: (i) Ray through F₁ emerges parallel to the principal axis; (ii) principal focus (focus).

Where the marks are

  • Labelled diagram: ray through F₁ refracted parallel to the principal axis (1 mark)
  • Names the point as principal focus/focus (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.