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It is observed that the… (Class 10 Science 2023, Q25b)

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ScienceCBSE Class 10 · Board exam 2023, set 31/1/1 · 2 marks · Very short answer

CBSE Class 10 Science 2023: question 25(b)

Set in the CBSE Class 10 board exam of 2023, paper 31/1/1, 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 answerCompetency-basedThe Human Eye and the Colourful World

It is observed that the power of an eye to see nearby objects as well as far off objects diminishes with age.

  1. (i)

    Give reason for the above statement.

    0 marks
  2. (ii)

    Name the defect that is likely to arise in the eyes in such a condition.

    0 marks
  3. (iii)

    Draw a labelled ray diagram to show the type of corrective lens used for restoring the vision of such an eye.

    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

Which muscles change the shape of the eye lens? What happens to them with age?

Hint 2

The defect is common in older people. A single lens type cannot fix both near and far vision, so think of a lens with two parts.

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) Reason: With age, the ciliary muscles gradually become weaker. The eye lens also loses its flexibility. So the eye can no longer change the focal length of its lens properly (its accommodation falls), and both near and far vision suffer.

    1 mark

  2. (ii) Defect: Presbyopia. When the person suffers from both near and far vision problems, this is presbyopia along with myopia.

    ½ mark

  3. (iii) Corrective lens: bifocal lens (diagram described in words):

    • Draw a spectacle lens divided into two halves.
    • Label the upper part concave lens (for distant vision).
    • Label the lower part convex lens (for near vision).
    ½ mark

Answer: (i) Weakening of the ciliary muscles and reduced flexibility of the eye lens; (ii) presbyopia; (iii) bifocal lens, with a concave upper part for distant vision and a convex lower part for near vision.

Where the marks are

  • Gradual weakening of the ciliary muscles (½ mark)
  • Reduced flexibility of the eye lens (½ mark)
  • Names presbyopia (½ mark)
  • Bifocal lens diagram with concave upper part and convex lower part, labelled (½ 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.