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Briefly explain how the… (Class 12 Physics 2023, Q25)

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

CBSE Class 12 Physics 2023: question 25

Set in the CBSE Class 12 board exam of 2023, paper 55/1/1, section B, question 25, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q25 · 2 marks · Very short answerSemiconductor Electronics: Materials, Devices and Simple Circuits

Briefly explain how the diffusion and drift currents contribute to the formation of potential barrier in a p-n junction diode.

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

Hints

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

Hint 1

Start with why carriers cross the junction at all — concentration difference.

Hint 2

What do the carriers leave behind, and what field does that create?

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. Due to the concentration gradient, holes diffuse from p to n side and electrons from n to p side, giving a diffusion current. They leave behind immobile ions (negative on p-side, positive on n-side) near the junction, forming a depletion (space charge) region.

    1 mark

  2. This space charge sets up an electric field from n to p, which drives minority carriers across the junction, giving a drift current opposite to the diffusion current. As diffusion continues, the field grows until drift current equals diffusion current (equilibrium, no net current); the potential difference then existing across the junction is the potential barrier.

    1 mark

Answer: Diffusion creates the space charge region; its field causes opposing drift; equilibrium (diffusion = drift) fixes the barrier potential.

Where the marks are

  • Diffusion due to concentration gradient forms space charge/depletion region of immobile ions (1 mark)
  • Electric field causes drift current opposite to diffusion; barrier potential at equality of the two (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 paper2023 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.