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Name two important processes… (Class 12 Physics 2023, Q32b)

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PhysicsCBSE Class 12 · Board exam 2023, set 55/5/1 · 5 marks · Long answer

CBSE Class 12 Physics 2023: question 32(b)

Set in the CBSE Class 12 board exam of 2023, paper 55/5/1, section D, question 32(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q32(b) · 5 marks · Long answerSemiconductor Electronics: Materials, Devices and Simple Circuits

Name two important processes involved in the formation of a p-n junction diode. With the help of a circuit diagram, explain the working of junction diode as a full wave rectifier. Draw its input and output waveforms. State the characteristic property of a junction diode that makes it suitable for rectification.

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

One process is due to a concentration difference and the other is due to the electric field of the depletion layer.

Hint 2

Use a centre-tapped transformer with two diodes. Track which diode is forward biased in each half cycle.

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. The two processes involved in forming a p-n junction are diffusion and drift.

    1 mark

  2. Circuit (described): The ac input is applied to the primary of a centre-tapped transformer. The secondary ends A and B are connected to the p-sides of diodes D₁ and D₂ respectively. The n-sides of both diodes are joined together, and the load resistor is connected between this common point and the centre tap of the transformer. The output is taken across .

    1 mark

  3. Working: During the half cycle when A is positive with respect to the centre tap, B is negative. So D₁ is forward biased and conducts, while D₂ is reverse biased, and current flows through . In the next half cycle, A is negative and B is positive. Now D₂ conducts and D₁ does not, and current flows through in the same direction. Thus output is obtained during both half cycles.

    1 mark

  4. Waveforms (described): The input is a sinusoidal ac voltage. The output across is a series of positive half-sine pulses in both half cycles; the negative halves are inverted, giving a pulsating dc. The pulses due to D₁ and D₂ alternate.

    1 mark

  5. Characteristic property: A junction diode conducts (has low resistance) only when forward biased and offers very high resistance when reverse biased. This unidirectional conduction makes it suitable for rectification.

    1 mark

Answer: Diffusion and drift; centre-tap full-wave rectifier with D₁ and D₂ conducting in alternate halves; output is unidirectional pulsating dc; diode conducts only in forward bias

Where the marks are

  • Names diffusion and drift (½ + ½ mark)
  • Circuit diagram of full-wave rectifier (1 mark)
  • Working: alternate conduction of D₁ and D₂ (1 mark)
  • Input and output waveforms (1 mark)
  • Property: conducts only in forward bias (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 55/5/1: 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.