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A wire of resistance R is… (Class 10 Science 2025, Q25a)

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ScienceCBSE Class 10 · Board exam 2025, set 31/1/1 · 2 marks · Very short answer

CBSE Class 10 Science 2025: question 25(a)

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

Q25(a) · 2 marks · Very short answerElectricity

A wire of resistance R is cut into three equal parts. If these three parts are then joined in parallel, calculate the total resistance of the combination so formed.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/1/1.

Hints

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

Hint 1

How does the resistance of a wire depend on its length?

Hint 2

Each piece is one-third as long. What is its resistance?

Hint 3

Add the reciprocals of the three equal resistances.

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. Resistance is proportional to length (). Each of the three equal parts therefore has resistance .

    ½ mark

  2. For resistors in parallel:

    ½ mark

  3. Substituting:

    ½ mark

  4. Therefore the total resistance of the combination is .

    ½ mark

Answer: R_p = R/9

Where the marks are

  • Finds the resistance of each part as (½ mark)
  • Writes the parallel-combination formula (½ mark)
  • Substitutes correctly (½ mark)
  • Gets (½ mark)

Revise the chapter

  • Chapter: Electricity (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Electricity, one at a time, marked against the answer key and marking points.Back to the full paper2025 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.