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A person suffering from… (Class 10 Science 2024, Q25)

questionbuddy.in/q/cbse-10-science-2024-31-4-1-q25-person-suffering-presbyopia-needs-bifocal

ScienceCBSE Class 10 · Board exam 2024, set 31/4/1 · 2 marks · Very short answer

CBSE Class 10 Science 2024: question 25

Set in the CBSE Class 10 board exam of 2024, paper 31/4/1, section B, question 25, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q25 · 2 marks · Very short answerCompetency-basedThe Human Eye and the Colourful World

A person suffering from presbyopia needs bifocal lens. If he needs two lens of power dioptre and dioptre, which one of these two lenses is for the correction of distant vision and what is its focal length ?

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/4/1.

Hints

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

Hint 1

Which type of lens corrects myopia (distant vision)? What is the sign of its power?

Hint 2

Use P = 1/f, with f in metres.

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. Distant vision is corrected by a concave (diverging) lens, which has negative power. So the lens of power ** D** is for distant vision.

    1 mark

  2. Focal length:

    1 mark

Answer: The −4.0 D lens corrects distant vision; its focal length is −0.25 m (−25 cm).

Where the marks are

  • Identifies the −4.0 D (concave) lens for distant vision (1 mark)
  • Calculates f = 1/P = −0.25 m (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 paper2024 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.