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The potential difference… (Class 12 Physics 2023, Q24)

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PhysicsCBSE Class 12 · Board exam 2023, set 55/5/1 · 2 marks · Very short answer

CBSE Class 12 Physics 2023: question 24

Set in the CBSE Class 12 board exam of 2023, paper 55/5/1, section B, question 24, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q24 · 2 marks · Very short answerCurrent Electricity

The potential difference applied across a given conductor is doubled. How will this affect (i) the mobility of electrons and (ii) the current density in the conductor ? Justify your answers.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 55/5/1.

Hints

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

Hint 1

Write mobility in terms of e, τ and m.

Hint 2

Express J using Ohm's law and the cross-sectional area.

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) There is no effect on mobility.

    ½ mark

  2. Mobility is . It depends only on the relaxation time and the mass, not on the applied voltage. Doubling doubles both and , so their ratio stays constant.

    ½ mark

  3. (ii) The current density doubles.

    ½ mark

  4. Current density is . Since and are fixed, , so doubling doubles .

    ½ mark

Answer: (i) Mobility unchanged; (ii) current density doubles

Where the marks are

  • Mobility unchanged (½ mark)
  • Justification or = constant (½ mark)
  • Current density doubles (½ mark)
  • Justification (½ 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 paper2023 board paper, set 55/5/1: 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.