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The current I_1 in a… (Class 12 Physics SQP 2025-26, Q23I)

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PhysicsCBSE Class 12 · Sample paper, session 2025-26 · 3 marks · Short answer

CBSE Class 12 Physics sample paper 2025-26: question 23(I)

From the official CBSE sample question paper for 2025-26, section C, question 23(I), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q23(I) · 3 marks · Short answerCurrent Electricity

The current in a wire is getting divided in two wires with currents and at a junction in a circuit.The currents in the three wires are related by .
(A) State the fundamental law from which this relation is derived.
(B) Explain the validation of law of conservation of energy in Kirchhoff's voltage law?

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2025-26.

Hints

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

Hint 1

Can charge pile up at a junction?

Hint 2

Potential difference is work done per unit charge.

Hint 3

What is the net potential change for a charge returning to its starting point?

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. (A) The relation is Kirchhoff's junction rule, which follows from the law of conservation of electric charge: charge cannot accumulate at a junction, so charge entering per second equals charge leaving per second.

    1 mark

  2. (B) Kirchhoff's voltage law states that the algebraic sum of changes in potential around any closed loop is zero: .

    1 mark

  3. A charge taken once round a closed loop returns to its starting point, i.e. to the same potential, so its net change in energy is zero. Hence the energy supplied by the emfs equals the energy dissipated in the resistors — this is the law of conservation of energy.

    1 mark

Answer: (A) Conservation of charge (junction rule); (B) KVL: net potential change round a closed loop is zero, so energy gained from sources = energy lost in resistors

Where the marks are

  • Identifies conservation of charge (1 mark)
  • States KVL as algebraic sum of potential changes round a loop = 0 (1 mark)
  • Explains this as conservation of energy for a charge going round the loop (1 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 2025-26: 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.