# Physics Questions and Answers – Semiconductor Electronics – p-n Junction

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Semiconductor Electronics – p-n Junction”.

1. What will happen when a p-n diode is reversed-biased?
a) No current flows
b) The depletion region is increased
c) The depletion region is reduced
d) The height of the potential barrier is reduced
View Answer

Answer: b
Explanation: When a p-n diode is reverse biased, its depletion region is widened. This is because the voltage at the cathode will be higher than at the anode. This has the effect of increasing or decreasing the effective resistance of the junction itself allowing or blocking current flow through the diode.

2. What will be the resistance measured by an ohmmeter, if a p-n diode is reverse biased?
a) Zero
b) Low
c) High
d) Infinite
View Answer

Answer: c
Explanation: When a p-n diode is reverse biased, it offers high resistance. Forward biasing of p-n junction diode offers low resistance. In the case of an ideal p-n junction, resistance is zero. So, the ohmmeter can measure zero resistance.

3. Find out the application of the diode.
a) Oscillator
b) Amplifier
c) Rectifier
d) Modulator
View Answer

Answer: c
Explanation: Diode is used as a rectifier. A rectifier diode allows current to pass in only one direction. A rectifier will be able to convert alternating current into direct current.
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4. Which of the following constitutes Zener diode?
a) Oscillator
b) Regulator
c) Rectifier
d) Filter
View Answer

Answer: b
Explanation: Zener diode can be used as a voltage regulator. They are in turn used as shunt regulators to regulate the voltage in relatively smaller circuits. Zener diode is obtained as a result of reverse biasing of a p-n junction diode.

5. Which of the following is a transistor material?
a) Chip
b) Insulator
c) Semiconductor
d) Metal
View Answer

Answer: c
Explanation: A transistor is a semiconductor device. It can act as a switch as well as an amplifier. Transistors are made up of semiconductor materials like silicon, germanium, etc. It is usually with at least three terminals for connection to an external circuit.
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6. Forward biasing of p-n junction diode offers high resistance.
a) True
b) False
View Answer

Answer: b
Explanation: No, this statement is false. Forward biasing of p-n junction diode offers low resistance and not high resistance. In the case of ideal p-n junction diodes, the resistance is zero.

7. What accounts for the flow of charge carriers in forward and reverse biasing of silicon p-n diode?
a) Drift in forward bias and diffusion in forward bias
b) Drift in reverse bias and diffusion in forward bias
c) Drift in both reverse and forward bias
d) Diffusion in both forward and reverse bias
View Answer

Answer: b
Explanation: Drift current flows from n-side to p-side while diffusion current flows from p-side to n-side. In forward biasing, diffusion current is more than the drift current and in reverse biasing, drift current is more than the diffusion current.
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8. Which of the following accounts for the presence of the potential barrier in the depletion layer?
a) Ions
b) Holes
c) Electrons
d) Forbidden band
View Answer

Answer: a
Explanation: The potential barrier in the depletion layer is due to the presence of immobile ions. The acceptor and donor atoms will gain negative and positive charges leading to p-n junction formation. Hence, acceptor and donor are immobile ions.

9. Which of the following is true in case of the unbiased p-n junction?
a) The high potential at n-side and low potential at p-side
b) The high potential at p-side and low potential at n-side
c) p and n both are at the same potential
d) Undetermined
View Answer

Answer: a
Explanation: In an unbiased p-n junction, the high potential is at the n-side and the low potential at the p-side. When the polarity of the battery is reversed, the p-n junction gets reverse biased and does not conduct electric current.
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10. What causes drift current in a p-n junction diode?
a) Electric field
b) Charge carriers density
c) Collision of electrons
d) Electric potential
View Answer

Answer: b
Explanation: Drift current is due to the high concentration of holes in the p-region and the high concentration of electrons in the n-region of the junction diode. The combined effect of the movement of minority charge carriers results in drift current.

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