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BHEL MCQs

Practice BHEL-oriented Electronics & Telecommunication Engineering MCQs with answers and explanations for technical exam preparation. Questions are arranged in pages of up to 100.

Question 304
Network TheoryKirchhoff Laws

Kirchhoff’s Current Law states that at any node?

  • AThe algebraic sum of currents is zero
  • BThe algebraic sum of voltages is always one
  • CPower is always zero
  • DResistance is always maximum
Report an error
Correct Answer: A. The algebraic sum of currents is zero
Explanation: KCL follows conservation of charge: the algebraic sum of currents entering and leaving a node is zero.
Reference: Standard network theory: kirchhoff laws
Question 305
Network TheoryKirchhoff Laws

Kirchhoff’s Voltage Law states that around any closed loop?

  • AThe algebraic sum of currents is zero
  • BThe algebraic sum of voltages is zero
  • CAll resistances are equal
  • DAll branch currents are equal
Report an error
Correct Answer: B. The algebraic sum of voltages is zero
Explanation: KVL follows conservation of energy: the algebraic sum of voltage rises and drops around a closed loop is zero.
Reference: Standard network theory: kirchhoff laws
Question 308
Network TheoryTransient Analysis

In DC steady state after a long time, an ideal capacitor behaves as a?

  • AShort circuit
  • BOpen circuit
  • CVoltage source of zero resistance in every case
  • DCurrent source
Report an error
Correct Answer: B. Open circuit
Explanation: For constant DC voltage, capacitor current i = C dv/dt becomes zero, so an ideal capacitor behaves as an open circuit in steady state.
Reference: Standard network theory: transient analysis
Question 311
Network TheoryNetwork Theorems

The superposition theorem is directly applicable to which type of network?

  • ALinear networks
  • BOnly nonlinear networks
  • COnly magnetic circuits
  • DOnly circuits with one source
Report an error
Correct Answer: A. Linear networks
Explanation: Superposition applies to linear circuits containing multiple independent sources; responses from individual sources are summed.
Reference: Standard network theory: network theorems
Question 312
Network TheoryNetwork Theorems

Thevenin’s theorem replaces a linear two-terminal network by?

  • AA current source in series with resistance
  • BA voltage source in series with resistance
  • CA voltage source in parallel with zero resistance only
  • DA capacitor and inductor only
Report an error
Correct Answer: B. A voltage source in series with resistance
Explanation: The Thevenin equivalent consists of an ideal voltage source Vth in series with an equivalent resistance or impedance.
Reference: Standard network theory: network theorems
Question 313
Network TheoryNetwork Theorems

Norton’s theorem replaces a linear two-terminal network by?

  • AA current source in parallel with resistance
  • BA voltage source in series with resistance
  • COnly a resistance
  • DOnly an inductor
Report an error
Correct Answer: A. A current source in parallel with resistance
Explanation: The Norton equivalent consists of an ideal current source IN in parallel with an equivalent resistance or impedance.
Reference: Standard network theory: network theorems
Question 321
Network TheoryNodal Analysis

In nodal analysis, the principal unknown quantities are usually?

  • ABranch powers
  • BNode voltages with respect to a reference node
  • CLoop charges
  • DOnly source currents
Report an error
Correct Answer: B. Node voltages with respect to a reference node
Explanation: Nodal analysis applies KCL to determine node voltages relative to a chosen reference or ground node.
Reference: Standard network theory: nodal analysis
Question 325
Network TheoryAC Circuit Analysis

Admittance is defined as?

  • AThe reciprocal of impedance
  • BThe square of impedance
  • CResistance plus reactance only
  • DVoltage divided by power
Report an error
Correct Answer: A. The reciprocal of impedance
Explanation: Admittance Y = 1/Z and is measured in siemens.
Reference: Standard network theory: ac circuit analysis
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Question 327
Network TheoryAC Circuit Analysis

The reciprocal of resistance is called?

  • AReactance
  • BConductance
  • CSusceptance
  • DInductance
Report an error
Correct Answer: B. Conductance
Explanation: Conductance G = 1/R and is measured in siemens.
Reference: Standard network theory: ac circuit analysis
Question 328
Network TheoryMesh Analysis

In mesh analysis, the principal unknown quantities are usually?

  • ANode voltages
  • BMesh currents
  • CCapacitances only
  • DSource powers only
Report an error
Correct Answer: B. Mesh currents
Explanation: Mesh analysis assigns a current to each independent mesh and uses KVL equations to solve for those currents.
Reference: Standard network theory: mesh analysis
Question 329
Network TheoryAC Circuit Analysis

In a purely inductive AC circuit, current ideally?

  • ALeads voltage by 90 degrees
  • BLags voltage by 90 degrees
  • CIs in phase with voltage
  • DLags voltage by 180 degrees
Report an error
Correct Answer: B. Lags voltage by 90 degrees
Explanation: For an ideal inductor, voltage leads current by 90 degrees; equivalently, current lags voltage by 90 degrees.
Reference: Standard network theory: ac circuit analysis
Question 330
Network TheoryMesh Analysis

Two adjacent meshes have currents I1 and I2 flowing through a common resistor R in opposite directions. The voltage drop associated with mesh I1 across the common resistor is?

  • AR(I1+I2)
  • BR(I1-I2)
  • CR/I1
  • DR(I2-I1) only regardless of reference
Report an error
Correct Answer: B. R(I1-I2)
Explanation: With the mesh currents opposing each other in the shared branch, the branch current referenced in I1's direction is I1-I2, so the drop is R(I1-I2).
Reference: Standard network theory: mesh analysis
Question 331
Network TheoryAC Circuit Analysis

In a purely capacitive AC circuit, current ideally?

  • ALags voltage by 90 degrees
  • BLeads voltage by 90 degrees
  • CIs in phase with voltage
  • DLeads voltage by 180 degrees
Report an error
Correct Answer: B. Leads voltage by 90 degrees
Explanation: For an ideal capacitor, current leads voltage by 90 degrees.
Reference: Standard network theory: ac circuit analysis
Question 332
Network TheorySource Transformation

A 12 V ideal voltage source in series with a 3 ohm resistor is source-transformed into?

  • AA 4 A current source in parallel with 3 ohm
  • BA 36 A current source in parallel with 3 ohm
  • CA 4 A current source in series with 3 ohm
  • DA 3 A current source in parallel with 4 ohm
Report an error
Correct Answer: A. A 4 A current source in parallel with 3 ohm
Explanation: The equivalent current is I = V/R = 12/3 = 4 A, and the same 3 ohm resistance is placed in parallel.
Reference: Standard network theory: source transformation
Question 334
Network TheorySource Transformation

A 5 A ideal current source in parallel with a 2 ohm resistor is equivalent to?

  • AA 2.5 V source in series with 2 ohm
  • BA 7 V source in series with 2 ohm
  • CA 10 V source in series with 2 ohm
  • DA 10 V source in parallel with 2 ohm
Report an error
Correct Answer: C. A 10 V source in series with 2 ohm
Explanation: The equivalent voltage is V = IR = 5×2 = 10 V, with the 2 ohm resistance in series.
Reference: Standard network theory: source transformation
Question 340
Network TheoryNetwork Theorems

When finding Thevenin resistance in a circuit containing dependent sources, dependent sources should generally be?

  • ATurned off like independent sources
  • BKept active
  • CAlways replaced by open circuits
  • DAlways replaced by short circuits
Report an error
Correct Answer: B. Kept active
Explanation: Dependent sources remain active because their values depend on circuit variables. A test source can be applied at the terminals to determine equivalent resistance.
Reference: Standard network theory: network theorems
Question 347
Network TheoryTransient Analysis

A first-order circuit is generally considered very close to its final steady-state value after approximately?

  • AOne time constant
  • BTwo time constants
  • CFive time constants
  • DTen milliseconds in every circuit
Report an error
Correct Answer: C. Five time constants
Explanation: After five time constants, a first-order response has completed more than 99% of its total transition and is commonly treated as essentially settled.
Reference: Standard network theory: transient analysis
Question 348
Network TheoryLaplace Transform

The Laplace transform of a unit step u(t) is?

  • A1
  • B1/s
  • Cs
  • D1/s^2
Report an error
Correct Answer: B. 1/s
Explanation: The unilateral or ordinary Laplace transform of the unit step for t>=0 is 1/s.
Reference: Standard network theory: laplace transform
Question 349
Network TheoryLaplace Transform

The Laplace transform of e^(-at)u(t) is?

  • A1/(s-a)
  • B1/(s+a)
  • Cs/(s+a)
  • Da/(s+a)
Report an error
Correct Answer: B. 1/(s+a)
Explanation: L{e^(-at)} = 1/(s+a), for the appropriate region of convergence.
Reference: Standard network theory: laplace transform
Question 350
Network TheoryLaplace Transform

The Laplace transform of sin(omega t)u(t) is?

  • As/(s^2+omega^2)
  • Bomega/(s^2+omega^2)
  • C1/(s+omega)
  • Domega/s^2
Report an error
Correct Answer: B. omega/(s^2+omega^2)
Explanation: The standard transform is L{sin(omega t)}=omega/(s^2+omega^2).
Reference: Standard network theory: laplace transform
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Question 351
Network TheoryNetwork Functions

For a network with zero initial conditions, its transfer function H(s) is generally defined as?

  • AInput divided by output
  • BOutput transform divided by input transform
  • COutput plus input
  • DOnly the denominator polynomial
Report an error
Correct Answer: B. Output transform divided by input transform
Explanation: With zero initial conditions, H(s)=Y(s)/X(s), the ratio of output transform to input transform.
Reference: Standard network theory: network functions
Question 352
Network TheoryNetwork Functions

The poles of a network transfer function are the values of s that make its?

  • ANumerator zero
  • BDenominator zero
  • CInput resistance zero only
  • DOutput voltage always one
Report an error
Correct Answer: B. Denominator zero
Explanation: Poles are roots of the denominator polynomial of the transfer function after common factors have been removed.
Reference: Standard network theory: network functions
Question 353
Network TheoryNetwork Functions

The zeros of a transfer function are the values of s that make its?

  • ANumerator zero
  • BDenominator zero
  • CTime constant infinite only
  • DSupply voltage zero
Report an error
Correct Answer: A. Numerator zero
Explanation: Zeros are roots of the numerator polynomial after common factors have been removed.
Reference: Standard network theory: network functions
Question 354
Network TheoryNetwork Functions

For a stable continuous-time LTI network with a rational transfer function, all poles must lie where in the s-plane for asymptotic stability?

  • AStrictly in the left half-plane
  • BStrictly in the right half-plane
  • COnly on the positive real axis
  • DAnywhere with positive real part
Report an error
Correct Answer: A. Strictly in the left half-plane
Explanation: For a causal rational continuous-time system to be asymptotically stable, its poles must have negative real parts, i.e. lie strictly in the left half-plane.
Reference: Standard network theory: network functions
Question 361
Network TheorySecond-Order Circuits

A series RLC natural response is underdamped when?

  • Aalpha is less than omega0
  • Balpha equals omega0
  • Calpha is greater than omega0
  • DR is always zero only
Report an error
Correct Answer: A. alpha is less than omega0
Explanation: The second-order response is underdamped when alphaomega0.
Reference: Standard network theory: second-order circuits
Question 363
Network TheorySecond-Order Circuits

Critical damping in a second-order series RLC circuit occurs when?

  • Aalpha=0
  • Balpha=omega0
  • Calpha=2omega0
  • Domega0=0
Report an error
Correct Answer: B. alpha=omega0
Explanation: Critical damping occurs at the boundary between oscillatory and nonoscillatory responses, where alpha equals omega0.
Reference: Standard network theory: second-order circuits
Question 366
Network TheoryTwo-Port Networks

The z-parameter equation for port 1 of a two-port network is?

  • AV1=z11 I1+z12 I2
  • BI1=z11 V1+z12 V2
  • CV1=z11 V1+z12 V2
  • DI1=z11 I1+z12 I2
Report an error
Correct Answer: A. V1=z11 I1+z12 I2
Explanation: By definition of impedance parameters, V1=z11I1+z12I2 and V2=z21I1+z22I2.
Reference: Standard network theory: two-port networks
Question 367
Network TheoryTwo-Port Networks

In ABCD or transmission parameters, which variables are commonly related for a two-port network?

  • AInput voltage/current to output voltage/current
  • BOnly the two port resistances
  • COnly input powers
  • DOnly output frequencies
Report an error
Correct Answer: A. Input voltage/current to output voltage/current
Explanation: ABCD parameters are particularly useful for cascaded networks because they relate input port variables to output port variables.
Reference: Standard network theory: two-port networks
Question 368
Network TheoryTwo-Port Networks

For cascaded two-port networks, the overall ABCD matrix is obtained by?

  • AAdding the individual ABCD matrices element by element
  • BMultiplying the individual ABCD matrices in cascade order
  • CTaking only the first matrix
  • DSubtracting all matrices
Report an error
Correct Answer: B. Multiplying the individual ABCD matrices in cascade order
Explanation: A key advantage of transmission parameters is that the ABCD matrix of a cascade is the ordered matrix product of the individual networks.
Reference: Standard network theory: two-port networks
Question 375
Network TheoryLaplace Transform

The inverse Laplace transform of 1/(s+4) is?

  • Ae^(-4t)u(t)
  • Be^(4t)u(t)
  • C4e^(-t)u(t)
  • Dsin(4t)u(t)
Report an error
Correct Answer: A. e^(-4t)u(t)
Explanation: The standard pair is 1/(s+a) ↔ e^(-at)u(t).
Reference: Standard network theory: laplace transform
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Question 390
Network TheoryAC Power

For a load with lagging power factor, power-factor correction is commonly achieved by connecting?

  • AA capacitor in parallel with the load
  • BAn additional resistor in series only
  • CA DC voltage source in parallel
  • DAn open circuit
Report an error
Correct Answer: A. A capacitor in parallel with the load
Explanation: A shunt capacitor supplies leading reactive power that offsets part of the load's lagging reactive power.
Reference: Standard network theory: ac power
Question 393
Network TheoryTwo-Port Networks

Two cascaded two-port networks have ABCD matrices M1 and M2. If M1 is followed by M2 from source to load, the overall transmission matrix is?

  • AM1+M2
  • BM2-M1
  • CM1M2
  • DM2/M1 element by element
Report an error
Correct Answer: C. M1M2
Explanation: For cascaded two-port networks, the overall ABCD matrix is the ordered product of the individual transmission matrices, M=M1M2 under the standard convention.
Reference: Standard network theory: two-port networks
Question 395
Network TheoryThree-Phase Circuits

The total real power in a balanced three-phase load is?

  • AVL IL cos(phi)
  • B√3 VL IL cos(phi)
  • C3 VL IL only
  • DVL IL sin(phi)
Report an error
Correct Answer: B. √3 VL IL cos(phi)
Explanation: Balanced three-phase real power is P=√3 VL IL cos(phi).
Reference: Standard network theory: three-phase circuits
Question 396
Communication SystemsCommunication Fundamentals

The information signal before modulation is commonly called the?

  • ACarrier signal
  • BBaseband or message signal
  • CLocal oscillator signal
  • DIntermediate-frequency signal only
Report an error
Correct Answer: B. Baseband or message signal
Explanation: The original information-bearing signal is called the message or baseband signal.
Reference: Standard communication systems: communication fundamentals
Question 398
Communication SystemsCommunication Fundamentals

The primary purpose of modulation in a communication system is to?

  • ATranslate a baseband signal to a suitable carrier frequency
  • BEliminate all noise completely
  • CMake information independent of bandwidth
  • DConvert every signal to DC
Report an error
Correct Answer: A. Translate a baseband signal to a suitable carrier frequency
Explanation: Modulation shifts information onto a carrier, enabling practical transmission, frequency allocation and efficient antennas.
Reference: Standard communication systems: communication fundamentals
Question 399
Communication SystemsCommunication Fundamentals

A basic electronic communication system normally consists of?

  • ATransmitter, channel and receiver
  • BOnly an oscillator and resistor
  • CRectifier, filter and regulator only
  • DMotor, generator and transformer
Report an error
Correct Answer: A. Transmitter, channel and receiver
Explanation: The basic communication chain contains a transmitter, a transmission medium or channel, and a receiver.
Reference: Standard communication systems: communication fundamentals
Question 400
Communication SystemsDemodulation

Coherent detection requires the receiver to have?

  • AA locally generated carrier with correct frequency and phase reference
  • BNo oscillator
  • COnly a diode and capacitor
  • DAn infinite bandwidth antenna
Report an error
Correct Answer: A. A locally generated carrier with correct frequency and phase reference
Explanation: Synchronous or coherent detection multiplies the received signal by a locally generated carrier synchronized in frequency and phase.
Reference: Standard communication systems: demodulation
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