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Give reasons for the… (Class 10 Science 2023, Q31)

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

CBSE Class 10 Science 2023: question 31

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

Q31 · 3 marks · Short answerCompetency-basedThe Human Eye and the Colourful World

Give reasons for the following :

  1. (a)

    Danger signals installed at airports and at the top of tall buildings are of red colour.

    0 marks
  2. (b)

    The sky appears dark to the passengers flying at very high altitudes.

    0 marks
  3. (c)

    The path of a beam of light passing through a colloidal solution is visible.

    0 marks

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

Hints

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

Hint 1

All three are explained by scattering of light.

Hint 2

Scattering depends on wavelength and on the presence and size of particles. Apply this to each case.

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) Red light has the longest wavelength among visible colours, so it is scattered the least by fog, smoke and air particles. A red signal therefore keeps its colour and can be seen clearly from a long distance.

    1 mark

  2. (b) At very high altitudes there is almost no atmosphere (air molecules and dust) to scatter sunlight. With no scattered light reaching the eyes, the sky appears dark instead of blue.

    1 mark

  3. (c) The particles in a colloidal solution are large enough to scatter light. The beam is scattered sideways by these particles and reaches our eyes, so its path becomes visible. This is the Tyndall effect.

    1 mark

Answer: (a) Red has the longest wavelength and is scattered least, so it is visible from far; (b) there is no atmosphere to scatter light at high altitude; (c) colloid particles scatter light (Tyndall effect).

Where the marks are

  • Red is least scattered (longest wavelength) and is seen from a distance (1 mark)
  • No scattering due to lack of atmosphere at great heights (1 mark)
  • Colloidal particles are big enough to scatter light (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from The Human Eye and the Colourful World, one at a time, marked against the answer key and marking points.Back to the full paper2023 board paper, set 31/1/1: 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.