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Define the following terms… (Class 10 Science 2023, Q30A)

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ScienceCBSE Class 10 · Board exam 2023, set 31/4/1 · 3 marks · Short answer

CBSE Class 10 Science 2023: question 30(A)

Set in the CBSE Class 10 board exam of 2023, paper 31/4/1, section C, question 30(A), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q30(A) · 3 marks · Short answerLight – Reflection and Refraction

Define the following terms in the context of a diverging mirror :

  1. (i)

    Principal focus

    1 mark
  2. (ii)

    Focal length

    1 mark

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 31/4/1.

Hints

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

Hint 1

A diverging mirror is a convex mirror. Reflected rays spread out.

Hint 2

Trace the reflected rays backwards behind the mirror. Where do they seem to meet?

Hint 3

Focal length is a distance measured from a particular point on the mirror.

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) Principal focus of a diverging (convex) mirror: the point on the principal axis from which rays parallel to the principal axis appear to diverge after reflection from the mirror.

    1 mark

  2. It lies behind the mirror and is virtual, because the reflected rays only appear to come from it.

    ½ mark

  3. (ii) Focal length: the distance between the pole (P) and the principal focus (F) of the mirror.

    1 mark

  4. For a spherical mirror it is half the radius of curvature, . For a convex mirror it is taken as positive by the sign convention.

    ½ mark

Answer: (i) Point on principal axis from which reflected rays (incident parallel to axis) appear to diverge; (ii) Distance between pole and principal focus

Where the marks are

  • Correct definition of principal focus of convex mirror (1 mark)
  • Notes it is behind the mirror and virtual (½ mark)
  • Focal length = distance from pole to principal focus (1 mark)
  • States / positive for convex 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 paper2023 board paper, set 31/4/1: 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.