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Draw a circuit diagram of a… (Class 12 Physics 2026, Q28)

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PhysicsCBSE Class 12 · Board exam 2026, set 55/5/1 · 3 marks · Short answer

CBSE Class 12 Physics 2026: question 28

Set in the CBSE Class 12 board exam of 2026, paper 55/5/1, section C, question 28, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q28 · 3 marks · Short answerSemiconductor Electronics: Materials, Devices and Simple Circuits

Draw a circuit diagram of a full-wave rectifier using p-n junction diodes. Explain its working and show the input-output waveforms.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 55/5/1.

Hints

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

Hint 1

You need a transformer whose secondary has a centre tap and two diodes.

Hint 2

In each half cycle, one diode is forward biased — check that current through the load is always in the same direction.

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. Circuit: AC input applied to the primary of a centre-tap transformer. The two ends A and B of the secondary are connected to the p-sides of diodes D₁ and D₂; the n-sides of both diodes are joined together and connected through the load resistance to the centre tap C. Output is taken across .

    1 mark

  2. Working: During the positive half cycle of input, end A is positive and B negative with respect to C; D₁ is forward biased and conducts, D₂ is reverse biased. Current flows through (from the diode junction towards C).
    During the negative half cycle, B is positive and A negative; D₂ conducts and D₁ is cut off. Current again flows through in the same direction. Thus output is obtained in both half cycles — full-wave rectification.

    1 mark

  3. Waveforms: Input — a sinusoidal AC voltage with positive and negative half cycles. Output across — a series of positive half-sine pulses, one for every half cycle (pulsating unidirectional DC), the pulses due to D₁ and D₂ alternating.

    1 mark

Answer: Centre-tap full-wave rectifier: D₁ conducts in positive half cycle, D₂ in negative half cycle; output across R_L is unidirectional for both halves (pulsating DC).

Where the marks are

  • Correct labelled circuit diagram with centre-tap transformer, two diodes and load (1 mark)
  • Working explained for both half cycles (1 mark)
  • Input and output waveforms (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 55/5/1: 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.