Semiconductor Electronics Materials Devices And Simple Circuits
30 previous year questions.
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Chapter Questions
30 MCQs
01
PYQ 2008
medium
physicsID: mht-cet-
The charge carriers in a -type semiconductor are
1
electrons only
2
holes only
3
holes in larger numbers and electrons in smaller numbers
4
holes and electrons in equal numbers
Official Solution
Correct Option: (3)
In a p-type semiconductor, holes are the majority charge carriers and electrons are minority charge carriers. So, holes are in larger numbers and electrons in smaller numbers.
02
PYQ 2016
medium
physicsID: mht-cet-
In an oscillator, for sustained oscillations, Barkhausen criterion is equal to ( voltage gain without feedback, feedback factor)
1
2
3
4
Official Solution
Correct Option: (3)
03
PYQ 2017
easy
physicsID: mht-cet-
Photodiode is a device
1
which is always operated in reverse bias
2
which is always operated in forward bias
3
in which photo current is independent of intensity of incident radiation
4
which may be operated in forward or reverse bias
Official Solution
Correct Option: (1)
Answer (a) which is always operated in reverse bias
04
PYQ 2018
medium
physicsID: mht-cet-
A transistor is used as a common emitter amplifier with a load resistance 2 K . the input resistance is 150 . Base current is changed by 20 A which results in a change in collector current by . The voltage gain of the amplifier is
1
900
2
1000
3
1100
4
1200
Official Solution
Correct Option: (2)
Given, load resistance Input resistance Change in collector current
Change in base current We know that,
05
PYQ 2019
medium
physicsID: mht-cet-
For a transistor, the current ratio is defined as the ratio of
1
collector current to emitter current
2
collector current to base current
3
base current to collector current
4
emitter current to collector current
Official Solution
Correct Option: (2)
The current amplification factor of a transistor for direct current (DC) is the ratio of collector current to the base current in common emitter configuration i.e.,
However, the ratio of collector current to the emitter current gives the value of current amplification factor in common base configuration, i.e.,
06
PYQ 2020
medium
physicsID: mht-cet-
Using Bohr’s quantization condition, what is the rotational energy in the second orbit for a diatomic molecule? (I = moment of inertia of diatomic molecule, = Planck’s constant)
1
2
3
4
Official Solution
Correct Option: (1)
Step 1: Bohr’s quantization condition. Bohr's quantization condition for rotational energy gives:
where is the quantum number, is Planck’s constant, and is the moment of inertia. Step 2: Energy in second orbit. For the second orbit, . Substituting into the equation gives the rotational energy in the second orbit as:
Step 3: Conclusion. Thus, the correct answer is (A) .
07
PYQ 2020
medium
physicsID: mht-cet-
In an oscillator, if is the feedback factor and is the gain of amplifier, then sustained oscillations are obtained when
1
2
3
4
Official Solution
Correct Option: (3)
Step 1: Condition for sustained oscillations. For sustained oscillations, the condition for feedback oscillators is: where is the amplifier gain and is the feedback factor.
Step 2: Conclusion. Sustained oscillations are obtained when .
08
PYQ 2020
medium
physicsID: mht-cet-
In a semiconductor, the number of holes and number of free electrons are represented as and , respectively. Which one of the following statements is TRUE for the semiconductor?
1
In an intrinsic semiconductor, .
2
In an extrinsic semiconductor, .
3
In an intrinsic semiconductor, .
4
In an intrinsic semiconductor, .
Official Solution
Correct Option: (1)
Step 1: Understanding intrinsic and extrinsic semiconductors. In an intrinsic semiconductor, the number of free electrons is equal to the number of holes because every electron that is excited to the conduction band leaves behind a hole. This means . Step 2: Conclusion. Thus, the correct answer is for an intrinsic semiconductor, corresponding to option (A).
09
PYQ 2020
medium
physicsID: mht-cet-
A prism having refractive index and refracting angle has one of the refracting surfaces silvered. The beam of light incident on the other refracting surface will retrace its path, if angle of incidence is
1
2
3
4
Official Solution
Correct Option: (4)
Step 1: Condition for retracing the path. For retracing, the ray must strike the silvered surface normally after refraction at the first surface. Step 2: Refraction at first surface. Let the angle of refraction inside the prism be . For normal incidence on the silvered face, Step 3: Applying Snell’s law.
Step 4: Conclusion.
10
PYQ 2020
medium
physicsID: mht-cet-
An electron of charge is revolving in a fixed orbit of radius with frequency . Its magnetic dipole moment is
1
2
3
4
Official Solution
Correct Option: (2)
Step 1: Magnetic moment formula. Magnetic dipole moment is given by:
Step 2: Calculating current.
Step 3: Area of circular orbit.
Step 4: Substituting values.
Step 5: Conclusion. The correct expression is .
11
PYQ 2020
medium
physicsID: mht-cet-
The gate represented in the given figure is
1
NOT
2
AND
3
OR
4
NOR
Official Solution
Correct Option: (1)
Step 1: Identifying the logic gate. The gate shown in the image is a NOT gate. A NOT gate is a basic digital logic gate that inverts the input signal, producing the opposite output. In the given figure, it shows an inversion of the input to output , indicating a NOT gate. Step 2: Conclusion. Thus, the gate represented is a NOT gate, corresponding to option (A).
12
PYQ 2020
medium
physicsID: mht-cet-
I–V characteristics for a junction diode is shown. The device is
1
LED
2
Solar cell
3
Photo cell
4
Zener diode
Official Solution
Correct Option: (2)
Step 1: Understanding the given I–V characteristic. The I–V graph shows that current flows even when the voltage is zero or negative. The curve lies in the fourth quadrant, indicating that the device supplies electrical power rather than consuming it. Such a characteristic is typical of a device that converts light energy into electrical energy. Step 2: Analyzing the options. (A) LED: An LED conducts mainly in forward bias and emits light. Its I–V characteristic does not show power generation in the fourth quadrant. Hence, this option is incorrect. (B) Solar cell: A solar cell generates current when illuminated and shows an I–V characteristic in the fourth quadrant. This exactly matches the given graph. Hence, this option is correct. (C) Photo cell: A photo cell mainly works on the photoelectric effect and does not show the same I–V characteristics as a junction diode solar cell. Hence, this option is incorrect. (D) Zener diode: A Zener diode operates in reverse breakdown region for voltage regulation and does not generate power. Thus, this option is incorrect. Step 3: Conclusion. Since the given I–V characteristic shows power generation and corresponds to a junction device operating in the fourth quadrant, the device is a solar cell.
13
PYQ 2020
medium
physicsID: mht-cet-
The ratio of speed of an electron in the ground state in an atom to the velocity of light (c) is
1
2
3
4
Official Solution
Correct Option: (3)
Step 1: Understanding the formula. The question involves the relationship between the speed of an electron and the velocity of light in the ground state of an atom, expressed using constants like Planck's constant, permittivity of free space, and the elementary charge. Step 2: Analyzing the options. (A) : This does not match the required form. (B) : Again, this is not the correct relationship. (C) : This matches the correct relationship for the ratio of electron speed to light speed. (D) : Incorrect as it introduces an extra factor of . Step 3: Conclusion. The correct answer is (C) as it correctly represents the relationship.
14
PYQ 2020
medium
physicsID: mht-cet-
A transistor is used as a common emitter amplifier with a load resistance of 2 k . The input resistance is 150 . Base current is changed by 20 , which results in a change in collector current by 1.5 mA. The amplified voltage gain of the amplifier is
1
500
2
1000
3
750
4
1250
Official Solution
Correct Option: (2)
Step 1: Calculate the current gain. The current gain (also called the current amplification factor) is the ratio of the change in collector current ( ) to the change in base current ( ):
Given that and , we have:
Step 2: Calculate the voltage gain. The voltage gain of the amplifier is the product of the current gain and the ratio of load resistance to the input resistance :
Given that and , we have:
Step 3: Conclusion. Thus, the amplified voltage gain of the amplifier is 1000, which corresponds to option (B).
15
PYQ 2020
medium
physicsID: mht-cet-
A donor impurity results in
1
conduction band just above the filled valence band
2
holes as majority carriers and electrons as minority carriers
3
production of n-type semiconductor
4
production of p-type semiconductor
Official Solution
Correct Option: (3)
Step 1: Understanding donor impurities. Donor impurities are pentavalent atoms such as phosphorus, arsenic, or antimony, which are added to a pure semiconductor like silicon or germanium. These atoms have five valence electrons, one more than required for covalent bonding.
Step 2: Effect on charge carriers. The extra electron provided by the donor impurity becomes free to move and contributes to electrical conduction. Hence, electrons become the majority charge carriers, while holes become minority carriers.
Step 3: Final conclusion. Since donor impurities increase the number of free electrons, they lead to the formation of an n-type semiconductor.
16
PYQ 2020
medium
physicsID: mht-cet-
In a transistor, doping level in base is increased slightly, the collector current and base current respectively
1
increases slightly, decreases slightly
2
decreases slightly, increases slightly
3
increases slightly, increases slightly
4
decreases slightly, decreases slightly
Official Solution
Correct Option: (2)
Step 1: Understand the role of base doping. The base region of a transistor is lightly doped to allow maximum charge carriers to pass into the collector region. Step 2: Effect of increased base doping. When base doping is increased slightly, recombination of charge carriers in the base increases. Step 3: Effect on collector current. Due to increased recombination, fewer charge carriers reach the collector, hence collector current decreases slightly. Step 4: Effect on base current. Increased recombination requires more carriers to be supplied to the base, so base current increases slightly.
17
PYQ 2020
medium
physicsID: mht-cet-
In a transistor amplifier, base-emitter junction is forward biased and collector-emitter junction is reverse biased. The current gain is
1
2
3
4
Official Solution
Correct Option: (4)
Step 1: Understanding current gain. In a transistor amplifier, the current gain is defined as the ratio of the change in collector current to the change in base current . This ratio indicates how much the base current is amplified in the collector circuit. The correct formula for current gain is . Step 2: Conclusion. Thus, the correct answer is (D) .
18
PYQ 2020
medium
physicsID: mht-cet-
For which logic gate is the following statement true? The output is high if and only if all inputs are high.
1
AND
2
OR
3
NOR
4
NAND
Official Solution
Correct Option: (1)
Step 1: Understand the given condition. The statement says the output is high only when all inputs are high. Step 2: Analyze logic gates. The AND gate gives a high output only when every input is high. Other gates do not satisfy this condition. Step 3: Conclusion. The described behavior matches that of an AND gate.
19
PYQ 2020
medium
physicsID: mht-cet-
Which one of the following symbols represents a photodiode?
1
Symbol (B)
2
Symbol (A)
3
Symbol (C)
4
Symbol (D)
Official Solution
Correct Option: (3)
Step 1: Recall symbol of photodiode. A photodiode is represented by a diode symbol with arrows directed towards the junction, indicating incident light. Step 2: Analyze given symbols. Among the given options, symbol (C) shows light rays incident on a diode junction. Step 3: Conclusion. Symbol (C) correctly represents a photodiode.
20
PYQ 2020
medium
physicsID: mht-cet-
For an ideal diode, the current in the following arrangement is
1
10 A
2
10 mA
3
20 mA
4
1 mA
Official Solution
Correct Option: (2)
Step 1: Understanding the circuit. For an ideal diode, the current will flow if the diode is forward biased. The voltage across the resistor is the difference between the supply voltage and the diode voltage. Since the diode is ideal, its forward voltage drop is considered zero. The current through the resistor can be found using Ohm's law:
where is the total voltage across the resistor, and is the resistance. Step 2: Calculating the current. Step 3: Conclusion. Thus, the current is 10 mA, which is option (B).
21
PYQ 2022
easy
physicsID: mht-cet-
In a p-type semiconductor
1
electrons are minority carriers and pentavalent atoms are dopants
2
electrons are majority carries and pentavalent atoms are dopants
3
holes are minority carriers and trivalent atoms are dopants
4
holes are majority carriers and trivalent atoms are dopants
A p-type semiconductor is a type of semiconductor where the majority charge carriers are holes, which are essentially the absence of electrons. The process of creating a p-type semiconductor involves doping a semiconductor, typically silicon, with an element that has fewer valence electrons than the semiconductor. This process creates "holes" that act as positive charge carriers.
Key Characteristics of p-Type Semiconductor:
1. The majority carriers in a p-type semiconductor are holes. Holes are essentially the spaces left when electrons move away, creating a positive charge in the material.
2. The minority carriers in a p-type semiconductor are electrons. These electrons are less common in a p-type semiconductor but still play a role in its conductivity.
3. The dopant used in a p-type semiconductor is typically a trivalent atom, meaning it has three valence electrons. Common dopants include elements like boron (B) or gallium (Ga). These elements create an electron deficiency, thereby creating holes in the semiconductor material.
Conclusion:
In a p-type semiconductor, the majority carriers are holes, and the dopants used are typically trivalent atoms.
Correct Answer: Option 3: Holes are minority carriers and trivalent atoms are dopants.
22
PYQ 2022
easy
physicsID: mht-cet-
A transistor is used as a common emitter amplifier with a load resistance 2 kΩ. The input resistance is 150 Ω. Base current is changed by 20 μA which results in a change in collector current by 1.5 mA. The voltage gain of the amplifier is
1
1100
2
1200
3
900
4
1000
Official Solution
Correct Option: (4)
The voltage gain of a common emitter amplifier can be calculated using the formula: Voltage Gain = - β * where: β is the current gain of the transistor, Load Resistance = 2 kΩ and Input Resistance = 150Ω. To find the voltage gain, we need to determine the value of β, which is the current gain of the transistor. The current gain (β) is defined as the ratio of the change in collector current (ΔIc) to the change in base current (ΔIb). β = Given that the change in collector current (ΔIc) is 1.5 mA and the change in base current (ΔIb) is 20 μA β = = 75 Now Voltage Gain = - β * Voltage Gain = -75 * = -75 * 13.333 = -1000 Since the voltage gain can be negative for a common emitter amplifier, the correct answer is (D) 1000.
23
PYQ 2024
medium
physicsID: mht-cet-
What is the output of a NAND gate when both inputs are HIGH?
1
2
3
4
Official Solution
Correct Option: (2)
A NAND gate (NOT-AND gate) is a fundamental digital logic gate that produces an output which is the negation of the AND gate. It is one of the most widely used gates in digital circuits, particularly because it is a universal gate, meaning any other logic gate can be constructed using only NAND gates. The truth table for a NAND gate is as follows:
Step 1: Analyze the given inputs.
Input A
Input B
Output Y (NAND)
0
0
1
0
1
1
1
0
1
1
1
0
When both inputs and are HIGH ( ):
In this case, , since the AND operation yields 1 when both inputs are 1.
Step 2: Apply the NOT operation.
Next, we negate the result of the AND operation:
Conclusion:
Thus, the output of the NAND gate is LOW ( ) when both inputs are HIGH. Therefore, the correct answer is .
24
PYQ 2025
easy
physicsID: mht-cet-
In a silicon semiconductor at room temperature, the intrinsic carrier concentration is . Calculate the energy band gap of the silicon if the intrinsic carrier concentration is given by:
Where:
- is the effective density of states in the conduction band,
- is the effective density of states in the valence band,
- is the Boltzmann constant,
- is the temperature.
1
2
3
4
Official Solution
Correct Option: (1)
We are given the formula for the intrinsic carrier concentration :
Rearranging the equation to solve for the energy band gap :
Substitute the known values:
Solving this, we get:
Thus, the energy band gap of silicon is .
25
PYQ 2025
medium
physicsID: mht-cet-
One end of a capillary tube is dipped in water, the rise of water column is ' '. The upward force of 98 dyne due to surface tension is balanced by the force due to the weight of the water column. The inner circumference of the capillary is ( surface tension of water )
When source of sound and observer both are moving towards each other, the observer will hear}
1
low frequency, low wavelength.
2
low frequency, high wavelength.
3
high frequency, low wavelength.
4
high frequency, high wavelength.
Official Solution
Correct Option: (3)
Step 1: Doppler Effect Concept
When the source and observer move towards each other, the relative speed of sound increases for the observer, leading to a higher apparent frequency ( ). Step 2: Wavelength Analysis
When the source moves towards the observer, the waves are "bunched up" in front of the source, leading to a decrease in the observed wavelength ( ). Step 3: Conclusion
Apparent frequency increases and apparent wavelength decreases. Final Answer: (C)
27
PYQ 2025
medium
physicsID: mht-cet-
Calculate the volume occupied by a particle in fcc unit cell if volume of unit cell is 1.6 10 cm .
1
5.44 10 cm
2
2.96 10 cm
3
8.37 10 cm
4
6.15 10 cm
Official Solution
Correct Option: (2)
Step 1: Concept
Packing efficiency of FCC .
Total volume of all particles in unit cell . Step 2: Total particle volume
Total Volume . Step 3: Volume of one particle
In FCC, number of atoms per unit cell .
Volume of one particle . Final Answer: (B)
28
PYQ 2025
medium
physicsID: mht-cet-
In a p-n junction diode, what happens to the width of the depletion region when the forward bias is increased?
1
It increases.
2
It decreases.
3
It remains the same.
4
It first increases and then decreases.
Official Solution
Correct Option: (2)
In a p-n junction diode, the depletion region is formed due to the diffusion of charge carriers across the junction, creating a region with no mobile charge carriers. When a forward bias is applied, the potential barrier is reduced, causing the width of the depletion region to decrease. As the forward bias increases, the electric field due to the bias overcomes the barrier, reducing the width of the depletion region. Thus, when the forward bias is increased, the width of the depletion region decreases.
29
PYQ 2025
medium
physicsID: mht-cet-
A liquid rises to a height of in a glass capillary . Another glass capillary having diameter of capillary is immersed in the same liquid. The rise of liquid in capillary is
The reverse saturation current (I0) of a silicon diode at 27°C is A. What will be the approximate value of I0 at 67°C? (Assume doubles for every 10°C rise in temperature)
