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Answer the following. (Class 12 Physics 2024, Q27)

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PhysicsCBSE Class 12 · Board exam 2024, set 55/5/1 · 3 marks · Short answer

CBSE Class 12 Physics 2024: question 27

Set in the CBSE Class 12 board exam of 2024, paper 55/5/1, section C, question 27, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q27 · 3 marks · Short answerSemiconductor Electronics: Materials, Devices and Simple Circuits

Answer the following.

  1. (a)

    Explain the characteristics of a p-n junction diode that makes it suitable for its use as a rectifier.

    0 marks
  2. (b)

    With the help of a circuit diagram, explain the working of a full wave rectifier.

    0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 55/5/1.

Hints

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

Hint 1

How does a diode behave under forward and under reverse bias?

Hint 2

With a centre-tapped transformer, the two ends are out of phase: which diode conducts 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. (a) A p-n junction diode conducts easily only when forward biased. Under reverse bias it allows almost no current, only a tiny reverse saturation current.

    This unidirectional conduction lets it pass only one polarity of an ac input, which converts ac into dc.

    1 mark

  2. (b) Circuit (described):

    • The ac input is applied to the primary of a centre-tapped transformer.
    • The ends A and B of the secondary are connected to the p-sides of diodes D₁ and D₂ respectively.
    • The n-sides of both diodes are joined together.
    • The load resistance is connected between this common point and the centre tap of the secondary.
    • The output is taken across .
    1 mark

  3. Working:

    • When A is positive with respect to the centre tap, B is negative, because it is out of phase. D₁ is then forward biased and conducts, while D₂ is reverse biased and does not. Current flows through .
    • In the next half cycle A is negative and B is positive. D₂ conducts and D₁ does not, and current flows through in the same direction.

    So a unidirectional (pulsating dc) output is obtained across in both halves of the ac cycle.

    1 mark

Answer: Diode conducts only in forward bias; in a centre-tap full wave rectifier D₁ and D₂ conduct in alternate half cycles, giving output in both halves.

Where the marks are

  • Unidirectional conduction (forward bias only) (1 mark)
  • Correct full wave rectifier circuit diagram (1 mark)
  • Explains the working over both half cycles (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 paper2024 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.