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MAHATRANSCO MCQs

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

Question 302
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 308
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 317
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
Question 319
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 320
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 321
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 322
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 323
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 324
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 325
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
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Question 332
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 334
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 337
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 338
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 339
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 340
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
Question 341
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 342
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 345
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 346
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 347
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
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Question 359
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 362
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 364
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 369
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
Question 374
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 375
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
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Question 376
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 380
Communication SystemsAmplitude Modulation

In conventional AM, the carrier component itself contains?

  • AAll of the message information
  • BNo message information by itself
  • COnly the highest audio frequency
  • DOnly digital data
Report an error
Correct Answer: B. No message information by itself
Explanation: The unmodulated carrier does not itself contain the message; the information resides in the sidebands.
Reference: Standard communication systems: amplitude modulation
Question 382
Communication SystemsDSB-SC & SSB

In a DSB-SC system, which component is suppressed?

  • ABoth sidebands
  • BCarrier
  • CMessage signal
  • DReceiver local oscillator
Report an error
Correct Answer: B. Carrier
Explanation: Double-sideband suppressed-carrier modulation transmits both sidebands while suppressing the carrier component.
Reference: Standard communication systems: dsb-sc & ssb
Question 385
Communication SystemsDSB-SC & SSB

One important advantage of SSB over conventional AM is?

  • ATwice the bandwidth requirement
  • BReduced bandwidth and improved power efficiency
  • CNeed for a much larger carrier
  • DComplete immunity to all noise
Report an error
Correct Answer: B. Reduced bandwidth and improved power efficiency
Explanation: SSB transmits one sideband and usually suppresses the carrier, saving both bandwidth and transmitted power.
Reference: Standard communication systems: dsb-sc & ssb
Question 386
Communication SystemsAM Demodulation

An envelope detector is most directly suitable for demodulating?

  • AProperly modulated conventional AM with carrier
  • BDSB-SC with no carrier under all conditions
  • CSSB-SC without carrier
  • DBPSK only
Report an error
Correct Answer: A. Properly modulated conventional AM with carrier
Explanation: A simple envelope detector can recover the message from conventional AM when a sufficiently strong carrier is present and overmodulation is avoided.
Reference: Standard communication systems: am demodulation
Question 387
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
Question 389
Communication SystemsAmplitude Modulation

In conventional amplitude modulation, which carrier parameter is varied according to the message signal?

  • AAmplitude
  • BFrequency
  • CPhase only
  • DPropagation velocity
Report an error
Correct Answer: A. Amplitude
Explanation: In AM, the carrier amplitude varies in accordance with the instantaneous message signal while carrier frequency and phase remain nominally constant.
Reference: Standard communication systems: amplitude modulation
Question 391
Communication SystemsAmplitude Modulation

For a single-tone AM wave, modulation index m is commonly equal to?

  • AMessage amplitude divided by carrier amplitude
  • BCarrier amplitude divided by message amplitude
  • CCarrier frequency divided by message frequency
  • DMessage frequency multiplied by carrier frequency
Report an error
Correct Answer: A. Message amplitude divided by carrier amplitude
Explanation: For standard sinusoidal AM, m=Am/Ac when the modulating and carrier amplitudes are expressed consistently.
Reference: Standard communication systems: amplitude modulation
Question 396
Communication SystemsFrequency Modulation

A major advantage of FM over conventional AM in many analog radio applications is better?

  • ANoise immunity
  • BDC power conversion
  • CCarrier suppression
  • DAntenna elimination
Report an error
Correct Answer: A. Noise immunity
Explanation: Because information is carried in frequency rather than amplitude, FM can provide improved rejection of amplitude noise and better noise performance under suitable conditions.
Reference: Standard communication systems: frequency modulation
Question 398
Communication SystemsFrequency Modulation

Pre-emphasis and de-emphasis in FM systems are used primarily to improve?

  • AHigh-frequency noise performance
  • BDC supply regulation
  • CAntenna mechanical strength
  • DCarrier power efficiency to 100%
Report an error
Correct Answer: A. High-frequency noise performance
Explanation: Pre-emphasis boosts higher message frequencies before transmission and de-emphasis restores the response at the receiver while reducing high-frequency noise.
Reference: Standard communication systems: frequency modulation
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