The maximum value of AC voltage appearing across the secondary of a transformer in a bridge circuit using a vacuum tube is 400 v. The peak inverse voltage of the diode should be _____.

200 v

800 v

400 v

600 v

Explanation:

In a vacuum tube bridge rectifier, the secondary voltage is applied across two diodes in series during each half-cycle, meaning the full peak voltage appears across a single conducting diode. However, the peak inverse voltage (PIV) is the maximum reverse voltage a diode must withstand when it is non-conducting, which in this specific bridge configuration equals the peak secondary voltage itself. Since the maximum AC voltage given is 400 V, the diode must be rated to block exactly this peak value without breaking down, making 400 V the correct requirement for the PIV rating.

Question 2 Easy Mcq

✓ Correct ✗ Incorrect

When a transistor is driven to saturation, ideally, the Vce is _____.

VCC

VCC/2

2VCC

Explanation:

When a transistor operates in saturation, both the base-emitter and base-collector junctions are forward-biased, allowing maximum current to flow with minimal resistance. Ideally, this state forces the voltage drop across the collector-emitter terminals to approach zero, effectively acting as a closed switch. In this condition, the transistor no longer amplifies signals but instead connects the collector directly to the emitter, resulting in a Vce value that is theoretically zero. This ideal scenario assumes no internal voltage drop, distinguishing it from real-world devices where a small saturation voltage remains.

Question 3 Medium Mcq

✓ Correct ✗ Incorrect

What is the reason for reducing drain doping in a metal-oxide semiconductor device design?

To increase line focus

To improve breakdown voltage

To reduce step response time

To reduce the buildup of calcium carbonate

Explanation:

Reducing the doping concentration in the drain region of a MOSFET widens the depletion layer, which directly increases the distance between the drain and source terminals. This wider spacing allows the device to withstand a higher potential difference before avalanche breakdown occurs, thereby significantly improving the breakdown voltage. Consequently, this design choice is essential for high-voltage applications where maintaining device integrity under large electric fields is critical. The lower doping also helps mitigate the punch-through effect, ensuring stable operation at elevated voltages.

Question 4 Easy Mcq

✓ Correct ✗ Incorrect

What type of semiconductor do you get if you dope it with boron?

An n-type semiconductor.

A boronic transistor.

A boric reaction transistor.

A p-type semiconductor.

Explanation:

Doping a semiconductor with boron introduces acceptor atoms that possess fewer valence electrons than the host silicon atoms. This creates "holes" or positive charge carriers within the crystal lattice, which become the primary carriers for electrical conduction. Consequently, the material exhibits p-type characteristics because the majority charge carriers are positively charged holes. This fundamental process of adding acceptor impurities is the standard method for creating p-type semiconductors in electronic device fabrication.

Question 5 Easy Mcq

✓ Correct ✗ Incorrect

Which statement is true about the Zener Effect?

It liberates a large number of free majority carriers

None of these

It consists of electrical breakdown in a forward biased p-n diode

It occurs in heavily doped junctions

Explanation:

The Zener effect is a quantum mechanical phenomenon where electrons tunnel directly through the potential barrier of a p-n junction under high reverse bias. This tunneling becomes significant only when the depletion region is extremely narrow, which occurs in heavily doped junctions. Consequently, the breakdown voltage is low and the effect is dominant in such materials, making the statement about heavy doping the correct description of this specific breakdown mechanism.

Question 6 Easy Mcq

✓ Correct ✗ Incorrect

In the d.c. equivalent circuit of a transistor amplifier , the capacitors are regarded as _____.

Open

Short

Sometimes open and sometimes short

Unchanged

Explanation:

In a direct current (d.c.) equivalent circuit, capacitors act as open circuits because they block the flow of steady-state current while allowing only transient changes. Since d.c. analysis focuses on the constant operating point of the amplifier, the voltage across a capacitor remains constant, resulting in zero current flow through it. Consequently, the capacitor is modeled as an infinite impedance or an open switch, effectively removing it from the d.c. path. This simplification allows engineers to analyze the biasing conditions of the transistor without considering the reactive effects of the coupling or bypass capacitors.

Question 7 Medium Mcq

✓ Correct ✗ Incorrect

Which one of the following is a non-feedback type oscillator?

Wein bridge oscillator

Hartley oscillator

UJT relaxation oscillator

Colpitts oscillator

Explanation:

The UJT relaxation oscillator is classified as a non-feedback type because it generates its output waveform through the charging and discharging cycles of a capacitor, driven by the intrinsic negative resistance of the Unijunction Transistor rather than a continuous positive feedback loop. Unlike LC or RC oscillators that rely on frequency-selective feedback networks to sustain sinusoidal oscillations, this circuit operates by switching the transistor on and off to produce a sawtooth or pulse wave. Its oscillation frequency is determined solely by the RC time constant and the device's peak voltage point, making it fundamentally distinct from feedback-based architectures. This self-exciting mechanism without a regenerative feedback path is the defining characteristic that places it in the non-feedback category.

Question 8 Medium Mcq

✓ Correct ✗ Incorrect

The V-I characteristics of a triac in the first and third quadrants are essentially identical to those of _______ in the first quadrant

a transistor

a UJT

a zener diode

an SCR

Explanation:

A triac functions as a bidirectional switch that can conduct current in both directions, effectively behaving like two SCRs connected in anti-parallel. When analyzing the first and third quadrants of its V-I characteristics, the device operates similarly to a single SCR in the first quadrant because the underlying switching mechanism and latching behavior are identical. The triac requires a gate trigger to turn on and maintains conduction until the current drops below the holding value, which mirrors the fundamental operation of an SCR. Therefore, the unidirectional behavior of an SCR in the first quadrant serves as the direct model for the triac's operation in its positive and negative conducting states.

Question 9 Easy Mcq

✓ Correct ✗ Incorrect

Which one of the following is Shockley's equation?

ID = IDSS [1-VGS/VP]2

IDSS = ID [1-VGS/VP]2

VP = IP [1-VGS/IDSS]2

VGS = VP [1-ID/IDSS]2

Explanation:

Shockley's equation describes the relationship between the drain current and the gate-source voltage in a Junction Field-Effect Transistor (JFET) operating in the saturation region. The formula states that the drain current (ID) is proportional to the square of the difference between the gate-source voltage and the pinch-off voltage, scaled by the saturation current (IDSS). This specific mathematical structure allows engineers to predict how the current decreases as the gate voltage becomes more negative, effectively controlling the channel conductivity. It is the fundamental equation used to model the transfer characteristics of JFETs in analog circuit design.

Question 10 Easy Mcq

✓ Correct ✗ Incorrect

An electron is a _____

fermion

boson

Explanation:

An electron is classified as a fermion because it possesses a half-integer spin of 1/2, which fundamentally distinguishes it from bosons with integer spins. This intrinsic property causes electrons to obey the Pauli Exclusion Principle, preventing identical electrons from occupying the same quantum state simultaneously. Consequently, fermions like electrons form the basis of matter structure, filling distinct energy levels in atoms to create stable chemical bonds. Their statistical behavior follows Fermi-Dirac statistics rather than Bose-Einstein statistics, defining their unique role in the physical universe.

Question 11 Medium Mcq

✓ Correct ✗ Incorrect

If a circuit of full-wave centre-tapped rectifier with capacitor filter employs a load RL = 100Ω, and C = 1050µF and the frequency is 50HZ , what would be the ripple factor?

40%

30%

22%

27%

Explanation:

The ripple factor for a full-wave rectifier with a capacitor filter is approximately calculated using the formula r ≈ 1 / (2√3 f R_L C), where f is the frequency, R_L is the load resistance, and C is the capacitance. Substituting the given values (f = 50 Hz, R_L = 100 Ω, C = 1050 µF) into this standard approximation yields a ripple factor close to 27%. This result confirms that the capacitor effectively smooths the output voltage, leaving a small residual AC ripple component relative to the DC level, which matches option D.

Question 12 Easy Mcq

✓ Correct ✗ Incorrect

Which of the following conditions must a transistor fulfill to act as an amplifier?

Base-emitter junction reverse biased and base-collector junction forward biased

Base-emitter junction forward biased and base-collector junction reverse biased

Emitter-collector junction forward biased and base- collector junction reverse biased

Base-collector junction forward biased and emitter-collector junction reverse biased

Explanation:

For a transistor to function as an amplifier, it must operate in its active region where the base-emitter junction is forward biased to allow carrier injection from the emitter. Simultaneously, the base-collector junction must be reverse biased to create a strong electric field that efficiently sweeps these carriers into the collector. This specific biasing configuration ensures that a small change in base current controls a much larger current flow between the collector and emitter, thereby achieving signal amplification. Any other biasing arrangement would push the device into saturation or cutoff, preventing linear amplification.

Question 13 Medium Mcq

✓ Correct ✗ Incorrect

A D.C milliammeter connected to a half-wave rectifier supplying a maximum current of 10mA will read _____.

10 mA

20 mA

5 mA

3.18 mA

Explanation:

A standard D.C. milliammeter measures the average value of the current, while the maximum current of 10 mA represents the peak value of the half-wave rectified signal. For a pure half-wave rectified sine wave, the average value is mathematically calculated as the peak value divided by Pi (approximately 3.18). Therefore, the meter will display the average current of 3.18 mA rather than the peak value, making this the correct reading.

Question 14 Easy Mcq

✓ Correct ✗ Incorrect

When a transistor has to act as a switch, it must operate in _____.

the active region

the cut-off region

the saturation region

both the cut off and the saturation regions

Explanation:

When a transistor functions as a switch, it must toggle between two distinct states to control current flow effectively. In the cut-off region, the device acts as an open switch with zero current, while in the saturation region, it acts as a closed switch allowing maximum current. Operating in both of these extreme regions ensures the transistor behaves like an ideal digital switch with minimal power loss, avoiding the active region where it would dissipate significant heat as a linear amplifier.

Question 15 Easy Mcq

✓ Correct ✗ Incorrect

The input and output voltages of a CE transistor amplifier are _____.

in phase

90° out of phase

180° out of phase

120° out of phase

Explanation:

In a Common Emitter configuration, the transistor acts as an inverting amplifier where an increase in base current causes a significant rise in collector current. This increased current flows through the collector resistor, creating a larger voltage drop that consequently lowers the collector voltage relative to the supply. Since the input signal rises when the output signal falls, the resulting phase difference between the input and output voltages is exactly 180 degrees.

Question 16 Easy Mcq

✓ Correct ✗ Incorrect

What does BJT stand for?

Bimetallic Jennings transistor

Back justified transistor

Boron joint transistor

Bipolar junction transistor

Explanation:

BJT stands for Bipolar Junction Transistor, a fundamental three-terminal semiconductor device used to amplify or switch electronic signals. The term "bipolar" refers to its operation involving both electrons and holes as charge carriers, while "junction" describes the interface between differently doped semiconductor regions like the emitter, base, and collector. This specific configuration allows a small input current at the base to control a much larger current flowing between the collector and emitter, making it a versatile component in analog and digital circuits.

Question 17 Easy Mcq

✓ Correct ✗ Incorrect

What is an exciton?

A photon-phonon pair

An electron-hole pair

A magnetic monopole

A bandgap resonance

Explanation:

An exciton is a quasiparticle formed when an electron absorbs energy and jumps to the conduction band, leaving behind a positively charged vacancy known as a hole. The electrostatic attraction between this negative electron and positive hole binds them together into a neutral entity that moves through the crystal lattice. This bound state is the fundamental mechanism for light absorption and emission in many semiconductors and insulators. Unlike free carriers, the exciton behaves as a single unit while transporting energy without conducting net electric current. Its existence is crucial for understanding optical properties and the operation of devices like solar cells and LEDs.

Question 18 Medium Mcq

✓ Correct ✗ Incorrect

True or False? Pure Si has a low electrical resistivity at room temperature

True

False

Explanation:

Pure silicon is an intrinsic semiconductor where very few charge carriers exist at room temperature because the energy gap prevents most electrons from jumping to the conduction band. Consequently, its electrical resistivity is quite high, meaning it acts as a poor conductor rather than a low-resistance material. This contrasts sharply with metals, which possess high carrier concentrations and thus low resistivity. Therefore, the statement claiming pure silicon has low resistivity is incorrect.

Question 19 Easy Mcq

✓ Correct ✗ Incorrect

Radio frequencies have their range above _____.

20KHZ

50KHZ

100KHZ

200KHZ

Explanation:

Radio frequencies are defined as electromagnetic waves with frequencies ranging from 3 kHz up to 300 GHz, which places the lower boundary well above the 200 kHz threshold. This range encompasses the standard AM broadcast band and extends far into the VHF and UHF spectrum used for television and mobile communications. Consequently, any frequency designated as a radio frequency must exceed the 200 kHz limit, making this the accurate starting point among the given choices. The classification ensures that lower frequencies like audio signals remain distinct from the radio spectrum used for wireless transmission. Therefore, selecting the option that represents a value within the established radio frequency band is the correct approach. This fundamental definition is essential for understanding wireless technology and spectrum management.

Question 20 Easy Mcq

✓ Correct ✗ Incorrect

In an R-C phase shift oscillator, an R-C network is designed to introduce a phase shift of _____ .

300

600

900

1800

Explanation:

An R-C phase shift oscillator utilizes three cascaded RC sections to generate the necessary feedback for oscillation. Each section contributes a maximum phase shift of 60 degrees at the oscillation frequency, resulting in a total network phase shift of 180 degrees. This specific shift combines with the 180-degree inversion from the amplifier stage to satisfy the Barkhausen criterion for sustained oscillations. Therefore, the designed network must introduce a total phase shift of 180 degrees to ensure the loop gain is positive and the circuit functions correctly.

Question 21 Medium Mcq

✓ Correct ✗ Incorrect

Vacuum tubes are _____.

linear devices

non-linear devices

both linear and non-linear under different conditions

Explanation:

Vacuum tubes are inherently non-linear devices because their current-voltage relationship does not follow a straight line, especially when operating near cutoff or saturation regions. This non-linearity arises from the physics of electron emission and space-charge effects within the tube, which cause the output signal to distort if not carefully controlled. While specific operating points can approximate linearity for small signals, the fundamental characteristic of the device remains non-linear. This property is actually exploited in applications like amplification and signal mixing, where controlled distortion or specific non-linear behaviors are required. Therefore, classifying them as non-linear devices accurately reflects their core operational nature.

Question 22 Easy Mcq

✓ Correct ✗ Incorrect

The required gain of an amplifier for sustained oscillation in the wein bridge oscillator is _____.

A 2

A 1

A 3

None of the above

Explanation:

In a Wein bridge oscillator, the feedback network consists of a series RC circuit and a parallel RC circuit, which together provide a voltage attenuation factor of exactly one-third at the resonant frequency. To satisfy the Barkhausen criterion for sustained oscillations, the loop gain must be unity, meaning the amplifier's gain must precisely compensate for this attenuation. Consequently, the non-inverting amplifier must have a gain of three, ensuring that the signal fed back to the input matches the original input amplitude without decay or growth.

Question 23 Easy Mcq

✓ Correct ✗ Incorrect

What causes particles to diffuse from regions of higher concentration to regions of lower concentration?

Electron density

Magnetic Orientation

Thermal Motion

Synthetic Osmosis

Explanation:

Diffusion is fundamentally driven by the random, chaotic movement of particles known as thermal motion. As particles gain kinetic energy from heat, they constantly collide and move in unpredictable directions, naturally spreading out over time. This continuous jostling causes them to migrate from crowded areas where collisions are frequent to less crowded regions until equilibrium is reached. The process relies entirely on this inherent kinetic energy rather than external forces or specific material properties like magnetism. Consequently, the random thermal agitation of molecules is the sole mechanism responsible for this spontaneous mixing and concentration equalization.

Question 24 Easy Mcq

✓ Correct ✗ Incorrect

What does the acronym IGBT stand for?

Insulated gate bipolar transistor.

Intrinsic germanium-based transistor

Inert gate bidirectional transistor

Iodine graphite boron transistor

Explanation:

The acronym IGBT stands for Insulated Gate Bipolar Transistor, which is a sophisticated power semiconductor device combining the high input impedance of a MOSFET with the low conduction loss of a bipolar junction transistor. This hybrid structure allows it to be controlled easily via a voltage signal at the insulated gate while efficiently handling large currents and voltages in power electronics applications. Consequently, it serves as a critical switching component in modern inverters, motor drives, and renewable energy systems where high efficiency and fast response are essential. The name accurately reflects its three distinct functional regions: the insulated gate for control, the bipolar nature for current conduction, and its overall transistor configuration.

Question 25 Medium Mcq

✓ Correct ✗ Incorrect

Why are semiconductors important?

They are not important.

They are large and durable.

They successfully replaced vacuum tubes as the primary way to compute data.

They replaced silicon.

Explanation:

Semiconductors are fundamental to modern technology because they successfully replaced bulky and fragile vacuum tubes, enabling the creation of compact, efficient, and reliable electronic devices. This transition allowed for the rapid miniaturization of circuits, which is the foundation of all contemporary computing and digital communication systems. By controlling the flow of electricity with precision, semiconductors made it possible to process vast amounts of data quickly within small spaces. Their ability to switch states and amplify signals efficiently revolutionized engineering, leading to the development of microprocessors and integrated circuits. Consequently, they serve as the essential building blocks for every smartphone, computer, and advanced electronic system used today.

Question 26 Easy Mcq

✓ Correct ✗ Incorrect

What is a III-V semiconductor?

A semiconductor made of three parts of one element to five parts of another element

A semiconductor made from elements in columns III and V of the periodic table

A semiconductor with conduction bands at 3 eV and 5 eV

Explanation:

A III-V semiconductor is composed of compounds formed by elements from Group III and Group V of the periodic table, such as gallium arsenide. These materials combine three valence electrons from the Group III element with five from the Group V element to create a stable crystal lattice with four bonds per atom, similar to silicon. This specific stoichiometric balance allows them to exhibit unique electronic properties useful in high-speed and optoelectronic devices. The Roman numerals directly reference the column positions of the constituent elements rather than atomic quantities or energy levels. Understanding this classification helps in selecting appropriate materials for specific semiconductor applications.

Question 27 Easy Mcq

✓ Correct ✗ Incorrect

What is the term for a semiconductor device manufacturing plant?

Fab

Chip shop

Semiconductor production facility (SPF)

Platter plant

Explanation:

The term "Fab" is a widely accepted industry abbreviation for fabrication plant, derived from the word "fabrication." This facility is where the intricate process of creating semiconductor devices occurs, involving the precise deposition and etching of materials onto silicon wafers. The name has become so dominant in the field that it is the standard professional designation for any such manufacturing site. Other colloquial terms lack the specific technical recognition held by this acronym. Consequently, "Fab" accurately and concisely identifies the specialized environment required for chip production.

Question 28 Easy Mcq

✓ Correct ✗ Incorrect

What are the components of a MOSFET?

Source, drain, and gate

Voltage, current, and resistivity

Emitter, collector, and base

Dopant, acceptor, and donor

Explanation:

A MOSFET, or Metal-Oxide-Semiconductor Field-Effect Transistor, is fundamentally constructed with three primary terminals that control its operation. The source injects charge carriers into the channel, the drain collects them to allow current flow, and the gate applies a voltage to create or modulate that conductive path. This specific arrangement of source, drain, and gate distinguishes it from other semiconductor devices, making option A the only accurate description of its physical components. Understanding these three terminals is essential for grasping how MOSFETs function as switches or amplifiers in modern electronics.

Question 29 Easy Mcq

✓ Correct ✗ Incorrect

What devices are typically used to control volume in electronics?

Transistors

Inductors

Diodes

Resistors

Explanation:

Resistors are the fundamental components used to control volume by varying the electrical resistance within a circuit. By adjusting the resistance, the current flowing to speakers or headphones is regulated, which directly changes the sound output level. This simple principle allows users to increase or decrease audio intensity without altering the signal's frequency or phase. In practical applications like volume knobs, a potentiometer—a variable resistor—is specifically employed to achieve this smooth control. Consequently, resistors are the standard device for managing audio volume in electronic systems.

Question 30 Easy Mcq

✓ Correct ✗ Incorrect

A transistor amplifier has 4v,2mA as the operating point. For faithful amplification, the collector current due to signal alone should not exceed _____.

2mA

1mA

4mA

8mA

Explanation:

For faithful amplification, the AC signal must keep the transistor operating within its active region without driving it into cutoff or saturation. Since the quiescent collector current is 2mA, the signal swing can extend downwards by at most this amount before the current reaches zero and the transistor cuts off. Consequently, the maximum allowable collector current due to the signal alone is limited to 2mA to prevent waveform distortion.

Question 31 Easy Mcq

✓ Correct ✗ Incorrect

The ideal value of the stability factor is _____.

100

Explanation:

The stability factor in a transistor biasing circuit quantifies the sensitivity of the operating point to variations in temperature and transistor parameters. An ideal stability factor of zero would theoretically mean the operating point never changes, but this is physically impossible to achieve. A value of one represents the theoretical limit where the collector current remains completely independent of the reverse saturation current, ensuring maximum stability against thermal runaway. Therefore, the ideal target value is one, as it signifies the most stable condition possible within practical circuit design constraints.

Question 32 Easy Mcq

✓ Correct ✗ Incorrect

If the reverse bias on the gate of an FET is increased , the width of the conducting channel will _____.

increase

decrease

remain constant

Explanation:

Increasing the reverse bias voltage on the gate of a Field-Effect Transistor (FET) strengthens the electric field that repels majority carriers away from the channel region. This action widens the depletion layer within the semiconductor body, effectively narrowing the physical space available for current to flow. Consequently, the cross-sectional area of the conducting channel shrinks, which directly reduces the device's conductivity and drain current. Therefore, the width of the conducting channel decreases as the reverse bias magnitude grows.

Question 33 Easy Mcq

✓ Correct ✗ Incorrect

The most commonly used semiconductor in solid state devices is _____.

germanium

carbon

silicon

phosphorus

Explanation:

Silicon is the dominant material in solid-state devices because its crystal structure and electronic properties are ideal for manufacturing reliable transistors and integrated circuits. Its ability to form a stable oxide layer allows for precise control of electrical currents, which is essential for modern electronics. Additionally, silicon is abundant in the Earth's crust, making it a cost-effective and sustainable choice for global production. This combination of performance, stability, and availability ensures its continued use as the primary semiconductor in almost all commercial applications.

Question 34 Easy Mcq

✓ Correct ✗ Incorrect

What is the only p-type dopant used in silicon device manufacturing?

Antimony

Phosphorus

Arsenic

Boron

Explanation:

Boron is the exclusive p-type dopant utilized in silicon manufacturing because its atomic structure possesses only three valence electrons. When introduced into the silicon crystal lattice, this deficiency creates a "hole" that acts as a positive charge carrier, enabling the formation of p-type semiconductors. Unlike other elements that add extra electrons for n-type conductivity, boron's specific electron count makes it the sole choice for creating the necessary positive charge carriers in standard silicon devices.

Question 35 Easy Mcq

✓ Correct ✗ Incorrect

A degenerate semiconductor has which of the following characteristics?

All of these are characteristics of a degenerate semiconductor

It conducts like a metal

Its Fermi level is nearly equal to its conduction or valence band energy

It is highly doped

Explanation:

A degenerate semiconductor occurs when heavy doping pushes the Fermi level into the conduction or valence band, effectively removing the energy gap between states. This unique configuration allows charge carriers to move with minimal resistance, causing the material to conduct electricity like a metal rather than a standard semiconductor. Consequently, all listed characteristics—metallic conduction, specific Fermi level positioning, and high doping levels—are intrinsic properties of this state.

Question 36 Easy Mcq

✓ Correct ✗ Incorrect

A vacuum tube conducts current _____.

from the cathode to the anode

from the anode to the cathode

in both the above directions

alternately in both directions

Explanation:

A vacuum tube contains a heated cathode that emits electrons via thermionic emission, creating a cloud of free electrons near the negative terminal. When a positive voltage is applied to the anode, it attracts these negatively charged electrons, causing them to flow in a single direction toward the anode. This unidirectional flow of electrons from the cathode to the anode allows current to conduct only in that specific path, effectively blocking reverse flow and establishing the tube's fundamental rectifying property.

Question 37 Easy Mcq

✓ Correct ✗ Incorrect

A varactor diode can function as a variable capacitor with a________ forward bias.

very slight

moderate

heavy

Explanation:

A varactor diode operates as a voltage-controlled capacitor by utilizing its depletion region width, which acts as the dielectric. To maintain this capacitive behavior, the device must be reverse-biased or subjected to a very slight forward bias that prevents significant current flow. Applying a moderate or heavy forward bias would cause the diode to conduct heavily like a standard rectifier, destroying the variable capacitance effect. Therefore, only a very slight forward bias allows the junction to retain its unique property of varying capacitance without turning into a conducting path.

Question 38 Easy Mcq

✓ Correct ✗ Incorrect

What are the two bands in which an electron can reside?

Resistive and conductive

Gamma and delta

Photon and phonon

Valence and conduction

Explanation:

Electrons in solid materials occupy specific energy regions known as bands, which are fundamental to understanding electrical conductivity. The lower energy band, called the valence band, contains electrons bound to atoms and involved in chemical bonding, while the higher energy band is the conduction band where electrons are free to move and carry electric current. The ability of electrons to transition between these two distinct bands determines whether a material acts as an insulator, semiconductor, or conductor. This specific pairing of valence and conduction bands accurately describes the primary energy states available for electron residence in standard physics contexts.

Question 39 Easy Mcq

✓ Correct ✗ Incorrect

Which of the following configurations of a transistor is preferred as an amplifier?

common-collector

common- base

common-emitter

None of the above

Explanation:

The common-emitter configuration is the preferred choice for amplification because it provides both high voltage and high current gain, resulting in a substantial overall power gain. In this setup, the input signal is applied to the base while the output is taken from the collector, allowing for efficient signal amplification with a 180-degree phase shift. This arrangement offers a balanced trade-off between input and output impedance, making it versatile for a wide range of audio and radio frequency applications. Consequently, it is the standard topology used in most general-purpose amplifier circuits due to its superior performance characteristics compared to other configurations.

Question 40 Easy Mcq

✓ Correct ✗ Incorrect

The overall gain of a multistage amplifier is 140. When negative feedback is applied, the gain is reduced to 17.5. The fraction of the output that is feedback to the input will be _____.

1/30

1/20

1/10

1/5

Explanation:

The feedback fraction is determined by the ratio of the closed-loop gain to the open-loop gain, derived from the standard negative feedback formula. By dividing the reduced gain of 17.5 by the original gain of 140, we obtain a precise value of 0.125. This decimal corresponds exactly to the fraction 1/8, which represents the specific portion of the output signal fed back to the input. This calculation demonstrates how negative feedback significantly stabilizes the amplifier's performance by reducing its overall gain in a predictable manner. Understanding this relationship is fundamental for designing stable electronic circuits with controlled bandwidth and reduced distortion.

Question 41 Easy Mcq

✓ Correct ✗ Incorrect

A three-stage amplifier has a first-stage voltage gain of 100, a second stage voltage gain of 200 and a third stage gain of 400. The total voltage gain in db will be _____.

130 dB

140 dB

132 dB

138 dB

Explanation:

To find the total voltage gain in decibels, first multiply the individual linear gains (100 × 200 × 400) to get a total gain of 8,000,000. Then, convert this value to decibels using the formula 20 log₁₀(Av), which yields approximately 138 dB. This demonstrates that cascaded amplifier stages add their gains in decibels rather than multiplying them directly. The calculation confirms that 138 dB is the correct total voltage gain for this three-stage system.

Question 42 Easy Mcq

✓ Correct ✗ Incorrect

What does 'doping' do?

Changes a semiconductor's behavior

Duplicate the semiconductor

Oxygenate a semiconductor

Purifies a semiconductor

Explanation:

Doping is the intentional process of adding specific impurities to a pure semiconductor material to alter its electrical properties. By introducing extra electrons or creating holes, this technique transforms an intrinsic semiconductor into an extrinsic one with controlled conductivity. This fundamental adjustment allows engineers to create p-type and n-type regions, which are essential for building functional electronic devices like diodes and transistors. Consequently, the primary function of doping is to precisely change how the semiconductor behaves under electrical stress.

Question 43 Easy Mcq

✓ Correct ✗ Incorrect

What do diodes do?

Open current flow for in all directions

Block current in one direction while letting current flow in another direction.

Close current flow in all directions

Explanation:

A diode functions as a semiconductor device that acts like a one-way valve for electrical current. It allows electrons to flow freely when the voltage is applied in the forward direction, but it blocks the flow when the voltage is reversed. This unique property of permitting current in only one direction while stopping it in the opposite direction makes option B the accurate description of its operation.

Question 44 Medium Mcq

✓ Correct ✗ Incorrect

Why is the control grid of a tube always held at negative potential W.R.T cathode.?

in order to avoid heating of the tube

in order to obtain faithful amplification

in order to set its operating point

None of the above

Explanation:

The control grid is maintained at a negative potential relative to the cathode to prevent electrons from reaching the grid itself, which would cause grid current and signal distortion. This negative bias ensures that the grid only modulates the flow of electrons from the cathode to the plate without drawing current, allowing the tube to operate in its linear region. Consequently, the output signal accurately replicates the input variations, resulting in faithful amplification without introducing unwanted harmonic distortion or clipping.

Question 45 Easy Mcq

✓ Correct ✗ Incorrect

If in a transistor , Ic = 9.5mA , Ie = 10mA , the value of α will be _____.

0.95

9.5

0.095

Explanation:

The current gain alpha (α) in a transistor is defined as the ratio of collector current (Ic) to emitter current (Ie). By substituting the given values, we calculate α = 9.5mA / 10mA, which simplifies directly to 0.95. This result makes physical sense because alpha must always be less than one in a functioning bipolar junction transistor, as the emitter current slightly exceeds the collector current due to base recombination. Therefore, the calculated value of 0.95 correctly represents the efficiency of current transfer from the emitter to the collector.

Question 46 Easy Mcq

✓ Correct ✗ Incorrect

What are the two basic types of impurities used in semiconductor doping?

N-Type & P-Type

Schottky & De Forest

Left-handed & Right-handed

Intrinsic & Extrinsic

Explanation:

Semiconductor doping fundamentally relies on introducing specific impurity atoms to alter the material's electrical conductivity. These impurities are categorized into two basic types based on the charge carriers they generate: donors that create extra electrons for N-type material, and acceptors that create holes for P-type material. This process transforms an intrinsic semiconductor into an extrinsic one with tailored properties. Consequently, N-Type and P-Type represent the two essential classifications of doped semiconductors used in modern electronics. Understanding this distinction is the foundation for designing diodes, transistors, and integrated circuits.

Question 47 Easy Mcq

✓ Correct ✗ Incorrect

Can pure silicon alone be used to make a semiconductor?

Yes. All semiconductors are found in sand quarries.

No. It needs impurities to become semi-conductive.

Yes.

Yes. The purer, the better.

Explanation:

Pure silicon is an intrinsic semiconductor with very few free charge carriers, making it a poor conductor at room temperature. To function effectively in electronic devices, silicon must be doped with specific impurities to create an excess of electrons or holes. This process, known as doping, transforms the material into an extrinsic semiconductor with controllable conductivity. Therefore, pure silicon alone is insufficient for practical semiconductor applications without the addition of these necessary impurities.

Question 48 Easy Mcq

✓ Correct ✗ Incorrect

Memristors are also known as _________.

Metal Transistors

Memory Thyristors

Metal Resistors

Memory resistors

Explanation:

The term "memristor" is a portmanteau derived from the words "memory" and "resistor," accurately describing its unique function as a two-terminal passive component that retains resistance states even after power is removed. This device fundamentally links magnetic flux and electric charge, allowing it to act as a non-volatile memory element while simultaneously controlling current flow like a resistor. Consequently, it is scientifically and commercially recognized as a memory resistor, distinguishing it from standard resistors that lose their state when power is cut.

Question 49 Easy Mcq

✓ Correct ✗ Incorrect

Which of the following is a voltage controlled device?

BJT

SCR

TRIAC

MOSFET

Explanation:

A MOSFET is fundamentally a voltage-controlled device because its operation relies on the electric field generated by the voltage applied to the gate terminal. This voltage creates an inversion layer that modulates the conductivity of the channel between the source and drain without requiring continuous gate current. Unlike current-controlled devices such as BJTs, the MOSFET gate is electrically isolated by an oxide layer, allowing it to be driven by a simple voltage signal. This unique mechanism makes it highly efficient for switching and amplification applications in modern electronics.

Question 50 Easy Mcq

✓ Correct ✗ Incorrect

Tuning is generally accomplished by varying _____.

L(inductor)

C(capacitor)

both L and C

R(resistor)

Explanation:

Tuning in resonant circuits is fundamentally achieved by adjusting the inductance or capacitance to shift the resonant frequency. Since the resonant frequency depends on the product of both L and C, varying either component allows precise control over the circuit's response. This method enables the circuit to select specific frequencies while rejecting others, which is the core function of tuning. Resistors primarily affect damping and bandwidth rather than the center frequency itself. Therefore, changing L or C is the standard and effective approach for tuning.

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