Physics – Semiconductor Electronics
Class 12 Physics (Chapter 14) • 100 Multiple Choice Questions
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Question 1
Energy gap (forbidden energy gap) for germanium is approximately:
Correct Answer: 0.7 eV
Question 2
Energy gap (forbidden energy gap) for silicon is approximately:
Correct Answer: 1.1 eV
Question 3
In an intrinsic semiconductor at absolute zero temperature (0 K), the electrical resistance is:
Correct Answer: Infinite (acts as a perfect insulator)
Question 4
When a pure semiconductor is doped with a pentavalent impurity (like Phosphorus or Arsenic), it becomes a:
Correct Answer: n-type semiconductor
Question 5
When a pure semiconductor is doped with a trivalent impurity (like Boron or Indium), it becomes a:
Correct Answer: p-type semiconductor
Question 6
In an n-type semiconductor, the majority charge carriers are:
Correct Answer: Electrons
Question 7
In a p-type semiconductor, the majority charge carriers are:
Correct Answer: Holes
Question 8
What is the net electrical charge of an n-type or p-type semiconductor crystal?
Correct Answer: Neutral (Zero net charge)
Question 9
In a p-n junction diode under forward bias:
Correct Answer: The depletion region width decreases and potential barrier is lowered
Question 10
In a p-n junction diode under reverse bias:
Correct Answer: The depletion region width increases and potential barrier is raised
Question 11
A p-n junction diode is primarily used as a:
Correct Answer: Rectifier (converting AC to DC)
Question 12
What is the maximum efficiency of a half-wave rectifier?
Correct Answer: 40.6%
Question 13
What is the maximum efficiency of a full-wave rectifier?
Correct Answer: 81.2%
Question 14
A Zener diode is specifically designed to operate in:
Correct Answer: Reverse bias breakdown region
Question 15
A Zener diode is commonly used as a:
Correct Answer: Voltage regulator
Question 16
An optoelectronic junction device that converts optical radiation into electrical energy (electricity) is:
Correct Answer: Photodiode / Solar cell
Question 17
A photodiode is generally operated under:
Correct Answer: Reverse bias
Question 18
A Light Emitting Diode (LED) emits spontaneous light when operated under:
Correct Answer: Forward bias
Question 19
A junction transistor consists of three regions known as:
Correct Answer: Emitter, Base, and Collector
Question 20
In a standard transistor, which section is the most heavily doped?
Correct Answer: Emitter
Question 21
In a standard transistor, which section is very thin and lightly doped?
Correct Answer: Base
Question 22
Which section of a transistor has the largest physical size?
Correct Answer: Collector
Question 23
In a transistor circuit, emitter current (I_E), collector current (I_C), and base current (I_B) are related as:
Correct Answer: I_E = I_C + I_B
Question 24
Current amplification factor (β) in common emitter configuration is defined as:
Correct Answer: ΔI_C / ΔI_B
Question 25
Current amplification factor (α) in common base configuration is defined as:
Correct Answer: ΔI_C / ΔI_E
Question 26
What is the relation between α and β current amplification factors?
Correct Answer: β = α / (1 - α) or α = β / (1 + β)
Question 27
Logic gates are digital circuits based on:
Correct Answer: Boolean algebra
Question 28
Which basic logic gate is known as an inverter?
Correct Answer: NOT gate
Question 29
Which gates are known as universal logic gates?
Correct Answer: NAND and NOR gates
Question 30
What is the Boolean expression for an AND gate with inputs A and B?
Correct Answer: Y = A · B
Question 31
What is the Boolean expression for an OR gate with inputs A and B?
Correct Answer: Y = A + B
Question 32
What is the Boolean expression for a NAND gate?
Correct Answer: Y = A · B (with entire bar over A·B)
Question 33
What is the Boolean expression for a NOR gate?
Correct Answer: Both (A) and (B)
Question 34
What is the output Y of an AND gate for inputs A = 1 and B = 0?
Correct Answer: 0
Question 35
What is the output Y of an OR gate for inputs A = 1 and B = 0?
Correct Answer: 1
Question 36
What is the output of a NOT gate if input A = 0?
Correct Answer: 1
Question 37
What is the barrier potential of a silicon p-n junction diode at room temperature?
Correct Answer: ≈ 0.7 V
Question 38
What is the barrier potential of a germanium p-n junction diode at room temperature?
Correct Answer: ≈ 0.3 V
Question 39
What constitutes the depletion region of a p-n junction?
Correct Answer: Immobile ionized donor and acceptor atoms (devoid of free mobile charge carriers)
Question 40
What is the direction of internal electric field across the depletion region of an unbiased p-n junction?
Correct Answer: From n-side to p-side
Question 41
Diffusion current in an unbiased p-n junction flows from:
Correct Answer: p-side to n-side
Question 42
Drift current in an unbiased p-n junction flows from:
Correct Answer: n-side to p-side
Question 43
At thermal equilibrium in an unbiased p-n junction, the net current across the junction is:
Correct Answer: Zero (diffusion current equals drift current in magnitude)
Question 44
What is dynamic resistance (r_d) of a p-n junction diode defined as?
Correct Answer: ΔV / ΔI (ratio of small change in voltage to corresponding change in current)
Question 45
Why are transistors preferred over bulky thermionic vacuum tubes?
Correct Answer: Small size, low power consumption, high reliability, and no filament warm-up time
Question 46
In common emitter amplifier configuration, what is the phase relationship between input signal voltage and output AC voltage?
Correct Answer: 180° out of phase (phase reversal)
Question 47
What is the voltage gain (A_v) of a common emitter amplifier in terms of current gain β and load resistance R_L, input resistance r_i?
Correct Answer: A_v = β · (R_L / r_i)
Question 48
What is the power gain of a common emitter amplifier equal to?
Correct Answer: Current gain (β) × Voltage gain (A_v)
Question 49
Which region of a transistor's output characteristics is used when operating it as a switch in 'ON' state (saturation)?
Correct Answer: Saturation region (collector-emitter voltage is very small, maximum collector current)
Question 50
Which region of a transistor's characteristics is used when operating it as a switch in 'OFF' state?
Correct Answer: Cut-off region (base current is zero, collector current is negligible)
Question 51
What is an integrated circuit (IC)?
Correct Answer: A microscopic electronic circuit consisting of millions of diodes, transistors, and resistors on a single semiconductor chip
Question 52
What is the output of a NAND gate if inputs A = 1 and B = 1?
Correct Answer: 0
Question 53
What is the output of a NOR gate if inputs A = 0 and B = 0?
Correct Answer: 1
Question 54
What is an XOR (Exclusive-OR) gate output for inputs A = 1 and B = 1?
Correct Answer: 0
Question 55
What is an XOR gate output for inputs A = 1 and B = 0?
Correct Answer: 1
Question 56
Which of the following describes avalanche breakdown in a p-n junction diode?
Correct Answer: Carrier multiplication due to impact ionization of atoms by thermally or field accelerated minority carriers at high reverse voltage
Question 57
Which of the following describes Zener breakdown in a heavily doped p-n junction diode?
Correct Answer: Direct quantum tunneling of electrons across a very narrow depletion layer due to high electric field
Question 58
What is the forbidden energy gap in insulators typically of the order of?
Correct Answer: > 3 eV (often 6 eV or more)
Question 59
What is the forbidden energy gap in metals (conductors)?
Correct Answer: Zero (conduction and valence bands overlap)
Question 60
What is solar cell material commonly made of?
Correct Answer: Silicon or Gallium Arsenide (GaAs)
Question 61
What is the relation between electron concentration (n_e), hole concentration (n_h), and intrinsic carrier concentration (n_i) in thermal equilibrium?
Correct Answer: n_e · n_h = n_i²
Question 62
In an intrinsic semiconductor, what is the relation between number density of electrons (n_e) and holes (n_h)?
Correct Answer: n_e = n_h = n_i
Question 63
In an n-type semiconductor, how does electron concentration (n_e) relate to hole concentration (n_h)?
Correct Answer: n_e >> n_h
Question 64
In a p-type semiconductor, how does hole concentration (n_h) relate to electron concentration (n_e)?
Correct Answer: n_h >> n_e
Question 65
What is electrical conductivity (σ) of a semiconductor given by in terms of charge carriers?
Correct Answer: σ = e (n_e μ_e + n_h μ_h)
Question 66
What is the valence of atoms used as pentavalent dopants for semiconductors?
Correct Answer: 5 valence electrons
Question 67
What is the valence of atoms used as trivalent dopants for semiconductors?
Correct Answer: 3 valence electrons
Question 68
Which of the following is a pentavalent impurity?
Correct Answer: Phosphorus (P)
Question 69
Which of the following is a trivalent impurity?
Correct Answer: Aluminum (Al)
Question 70
What is a donor energy level in an n-type semiconductor?
Correct Answer: Located just below the conduction band edge
Question 71
What is an acceptor energy level in a p-type semiconductor?
Correct Answer: Located just above the valence band edge
Question 72
Why are semiconductor devices preferred over thermionic valves?
Correct Answer: Low operating voltage, no heating time, small size, and high durability
Question 73
What is the output of an OR gate followed by a NOT gate (OR-NOT or NOR gate) for inputs A = 0, B = 0?
Correct Answer: 1
Question 74
What is the output of an AND gate followed by a NOT gate (AND-NOT or NAND gate) for inputs A = 1, B = 1?
Correct Answer: 0
Question 75
In a common-emitter transistor circuit, if collector current changes by 2 mA when base current changes by 20 µA, what is the current gain β?
Correct Answer: 100
Question 76
What is the value of current gain α if current gain β of a transistor is 99?
Correct Answer: 0.99
Question 77
What is the ripple frequency in the output of a full-wave rectifier supplied with 50 Hz AC?
Correct Answer: 100 Hz
Question 78
What is the ripple frequency in the output of a half-wave rectifier supplied with 50 Hz AC?
Correct Answer: 50 Hz
Question 79
What is the purpose of filter circuits (like capacitors and inductors) in a rectifier power supply?
Correct Answer: To remove AC ripples and smooth out the pulsating DC into steady DC
Question 80
Which of the following semiconductor devices emits monochromatic coherent light in lasers?
Correct Answer: Semiconductor Laser Diode
Question 81
What is the electrical conductivity of an intrinsic semiconductor at room temperature compared to metals?
Correct Answer: Much smaller than metals but much larger than insulators
Question 82
What happens to the depletion region of a p-n junction when forward voltage is increased?
Correct Answer: It shrinks / narrows down further
Question 83
What is the behavior of a p-n junction diode under ideal conditions in forward bias?
Correct Answer: Zero resistance (closed switch)
Question 84
What is the behavior of a p-n junction diode under ideal conditions in reverse bias?
Correct Answer: Infinite resistance (open switch)
Question 85
Which of the following circuits uses a bridge rectifier with 4 diodes?
Correct Answer: Full-wave bridge rectifier
Question 86
How many diodes are required in a center-tap full-wave rectifier circuit?
Correct Answer: 2 diodes
Question 87
How many diodes are required in a half-wave rectifier circuit?
Correct Answer: 1 diode
Question 88
What is the primary function of base region in a bipolar junction transistor?
Correct Answer: To control the flow of charge carriers from emitter to collector
Question 89
In a common-base transistor connection, the input signal is applied between:
Correct Answer: Emitter and Base
Question 90
In a common-emitter transistor connection, the input signal is applied between:
Correct Answer: Base and Emitter
Question 91
What is the logic operation performed by a combination of NOT gate followed by an OR gate (or equivalent truth table)?
Correct Answer: Depends on specific composite wiring (like implication or custom gates)
Question 92
What is De Morgan's First Theorem in Boolean algebra?
Correct Answer: (A + B)̄ = Ā · B̄
Question 93
What is De Morgan's Second Theorem in Boolean algebra?
Correct Answer: (A · B)̄ = Ā + B̄
Question 94
What is the result of Boolean expression A + Ā?
Correct Answer: 1
Question 95
What is the result of Boolean expression A · Ā?
Correct Answer: 0
Question 96
What is the result of Boolean expression A + 1?
Correct Answer: 1
Question 97
What is the result of Boolean expression A · 0?
Correct Answer: 0
Question 98
What is the result of Boolean expression A · 1?
Correct Answer: A
Question 99
What is the result of Boolean expression A + 0?
Correct Answer: A
Question 100
What is the main advantage of digital electronics (using binary numbers and logic gates) over analog electronics?
Correct Answer: Higher immunity to noise, greater accuracy, and ease of data storage and processing
