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Draw the circuit arrangement… (Class 12 Physics 2023, Q32a)

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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(a)

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

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

Draw the circuit arrangement for studying V-I characteristics of a p-n junction diode in (i) forward biasing and (ii) reverse biasing. Draw the typical V-I characteristics of a silicon diode. Describe briefly the following terms : (i) minority carrier injection in forward biasing and (ii) breakdown voltage in reverse biasing.

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

In forward bias, p is connected to + and you need a milliammeter. In reverse bias, the connections flip and you use a microammeter.

Hint 2

Think about where electrons and holes end up after crossing the junction in forward bias, and what happens to the reverse current at a critical voltage.

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. (i) Forward-bias circuit (described): A battery is connected through a rheostat (potential divider) and a key so that its positive terminal goes to the p-side of the diode and its negative terminal to the n-side. A milliammeter is in series with the diode and a voltmeter is connected across the diode.

    1 mark

  2. (ii) Reverse-bias circuit (described): The battery connections are reversed, so the positive terminal goes to the n-side and the negative terminal to the p-side. The battery is applied through a potential divider. A microammeter is in series with the diode, because the reverse current is very small, and a voltmeter is connected across the diode.

    1 mark

  3. V–I characteristics of a Si diode (described): In the forward-bias quadrant, the current is negligible up to the threshold (cut-in) voltage of about 0.7 V. Beyond this, the current (in mA) rises steeply, almost exponentially. In the reverse-bias quadrant, a very small, nearly constant reverse current (in µA) flows. At the breakdown voltage , the reverse current suddenly increases sharply.

    1 mark

  4. (i) Minority carrier injection: In forward bias the barrier is lowered. Electrons from the n-side diffuse across the depletion region into the p-side, where they are minority carriers. Holes from the p-side cross into the n-side, where they are minority carriers. This injection of minority carriers across the junction produces the forward current.

    1 mark

  5. (ii) Breakdown voltage: This is the reverse-bias voltage at which the reverse current, which is almost constant until then, suddenly increases sharply, while the voltage remains nearly constant.

    1 mark

Answer: Forward and reverse bias circuits, Si V–I curve (knee ≈ 0.7 V, sharp rise at breakdown); definitions of minority carrier injection and breakdown voltage

Where the marks are

  • Forward-bias circuit (1 mark)
  • Reverse-bias circuit (1 mark)
  • V–I characteristic curve (1 mark)
  • Explanation of minority carrier injection (1 mark)
  • Definition of breakdown voltage (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.