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If copper wire is… (Class 12 Physics SQP 2024-25, Q12)

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PhysicsCBSE Class 12 · Sample paper, session 2024-25 · 1 mark · MCQ

CBSE Class 12 Physics sample paper 2024-25: question 12

From the official CBSE sample question paper for 2024-25, section A, question 12, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q12 · 1 mark · MCQCurrent Electricity

If copper wire is stretched to make its radius decrease by 0.1%, then the percentage change in its resistance is approximately

  1. (A)–0.4%
  2. (B)+0.8%
  3. (C)+0.4%
  4. (D)+0.2%

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

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

Hint 1

Volume stays constant when a wire is stretched.

Hint 2

Express R in terms of r only.

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. Stretching keeps the volume constant, so . Then .

    ½ mark

  2. . The answer is (C).

    ½ mark

Answer: +0.4%, option (C)

Where the marks are

  • (0.5 mark)
  • +0.4% (0.5 mark)

Revise the chapter

Practise this chapterBoard-style questions from Current Electricity, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2024-25: 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.