The PN Junction and its Biasing

The PN Junction and its Biasing MDCAT MCQs with answers

9 past paper MCQs on The PN Junction and its Biasing, from the Electronics unit of MDCAT Physics. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

Read the notes first Practise the unit as a quiz

1.A diode characteristic curve is a plot between: (MDCAT 2024)

  1. current and time
  2. voltage and time
  3. voltage and current
  4. reverse voltage and forward voltage
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Correct answer: (c) voltage and current

The characteristic curve of a diode plots the current through it against the voltage across it.

2.Which of the following is NOT true about an LED? (UHS MDCAT 2017)

  1. two wires, called leads, are attached to an LED
  2. while connecting it in a circuit, the longer lead of the LED is always connected to the positive terminal of the battery
  3. while connecting it in a circuit, the shorter lead of the LED is always connected to the positive terminal of the battery
  4. an LED can be used to detect weak current
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Correct answer: (c) while connecting it in a circuit, the shorter lead of the LED is always connected to the positive terminal of the battery

The longer lead is the anode and goes to the positive terminal, so the statement about the shorter lead is the false one.

3.Which of the following is false? (UHS MDCAT 2017)

  1. in a p-type substance the majority charge carriers are holes
  2. during forward biasing of a diode the width of the depletion region decreases
  3. the leakage current is due to minority charge carriers
  4. none of the given options
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Correct answer: (d) none of the given options

All three statements are correct, so none of them is false.

4.Which of the following act as a semiconductor? (NUMS MDCAT 2025)

  1. Iron
  2. Silicon
  3. Zinc
  4. Tungsten
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Correct answer: (b) Silicon

Silicon is the tetravalent element of which most semiconductor devices are made.

5.The current in forward biased PN junction is mainly due to: (SZABMU MDCAT 2025)

  1. Majority carriers
  2. Minority carriers
  3. leakage carrier
  4. Thermionic emission
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Correct answer: (a) Majority carriers

Forward bias narrows the barrier, so the majority carriers cross in numbers.

6.When the PN junction is reverse-biased, its reverse current is of the order of: (KMU MDCAT 2024)

  1. Gigamperes
  2. Kiloamperes
  3. Megaamperes
  4. Microamperes
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Correct answer: (d) Microamperes

Reverse bias leaves only the small leakage of the minority carriers, of the order of microamperes.

7.Q.168 When the temperature of semiconductor suddenly drops to zero kelvin, then a semiconductor acts as: (UHS MDCAT 2023)

  1. Conductor
  2. Semi-conductor
  3. Super conductor
  4. Insulator
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Correct answer: (d) Insulator

At absolute zero no electron has the energy to cross the gap, so no charge can move.

8.Transistors can be used as: (PMC MDCAT 2022)

  1. Half-wave rectifier
  2. Full-wave rectifier
  3. Photocell
  4. Switch
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Correct answer: (d) Switch

A transistor can be driven fully on or fully off, which makes it a switch.

9.Which of the following is not true about LEDs? (UHS MDCAT 2017)

  1. There are two wires (called leads) attached to an LED
  2. While connecting to a circuit, the longer lead of LED is always connected to the positive terminal of the battery
  3. While connecting to a circuit, the shorter lead of LED is always connected to the positive terminal of the battery
  4. LED can be used to detect weak current
Show answer

Correct answer: (c) While connecting to a circuit, the shorter lead of LED is always connected to the positive terminal of the battery

The long lead is the anode and goes to the positive terminal, so the third statement is the false one.

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