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Briefly explain the two… (Class 12 Physics 2026, Q26)

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PhysicsCBSE Class 12 · Board exam 2026, set 55/1/1 · 3 marks · Short answer

CBSE Class 12 Physics 2026: question 26

Set in the CBSE Class 12 board exam of 2026, paper 55/1/1, section C, question 26, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q26 · 3 marks · Short answerSemiconductor Electronics: Materials, Devices and Simple Circuits

Briefly explain the two important processes that occur during the formation of a p-n junction.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 55/1/1.

Hints

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

Hint 1

Carriers move for two reasons: a difference in concentration, and an electric field.

Hint 2

Think about what the immobile ions left near the junction create, and how that affects minority carriers.

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. Diffusion: When the junction forms, there is a concentration gradient across it. Holes diffuse from the p-side to the n-side, and electrons from the n-side to the p-side. This produces the diffusion current, directed from p to n.

    1 mark

  2. Diffusion leaves behind uncovered immobile ions: positive donor ions on the n-side and negative acceptor ions on the p-side. This forms the depletion layer, a region with no free charge carriers, and sets up a junction electric field (barrier potential) directed from n to p.

    1 mark

  3. Drift: The junction field sweeps minority carriers across the junction, electrons from p to n and holes from n to p. This produces the drift current, opposite to the diffusion current. Diffusion current initially exceeds drift current. Equilibrium is reached when the two are equal, so the net current is zero.

    1 mark

Answer: Diffusion of majority carriers, which creates the depletion layer and barrier potential; drift of minority carriers under the junction field, which balances diffusion at equilibrium.

Where the marks are

  • Explains diffusion of majority carriers and the diffusion current (1 mark)
  • Formation of the depletion region and barrier field (1 mark)
  • Drift of minority carriers and the equilibrium of the two currents (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Semiconductor Electronics: Materials, Devices and Simple Circuits, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 55/1/1: 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.