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SAIL MCQs

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

Question 301

Network TheoryAC Circuit Analysis

At 50 Hz, the inductive reactance of a 0.1 H inductor is closest to?

A3.14 ohm
B31.4 ohm
C50 ohm
D314 ohm

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Correct Answer: B. 31.4 ohm

Explanation: XL = 2πfL = 2π×50×0.1 ≈ 31.4 ohm.

Reference: Standard network theory: ac circuit analysis

Question 302

Network TheoryAC Circuit Analysis

At 50 Hz, the capacitive reactance magnitude of a 100 microfarad capacitor is closest to?

A3.18 ohm
B31.8 ohm
C100 ohm
D318 ohm

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Correct Answer: B. 31.8 ohm

Explanation: XC = 1/(2πfC) = 1/(2π×50×100×10^-6) ≈ 31.8 ohm.

Reference: Standard network theory: ac circuit analysis

Question 303

Network TheoryAC Circuit Analysis

A series circuit has R = 3 ohm and inductive reactance XL = 4 ohm. The magnitude of its impedance is?

A1 ohm
B5 ohm
C7 ohm
D12 ohm

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Correct Answer: B. 5 ohm

Explanation: For Z = R+jXL, |Z| = sqrt(R^2+XL^2) = sqrt(9+16) = 5 ohm.

Reference: Standard network theory: ac circuit analysis

Question 304

Network TheoryAC Circuit Analysis

A series circuit has R = 6 ohm, XL = 8 ohm and negligible capacitive reactance. If supplied by 100 V RMS, the current magnitude is?

A5 A
B10 A
C12.5 A
D16.67 A

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Correct Answer: B. 10 A

Explanation: |Z| = sqrt(6^2+8^2) = 10 ohm, so I = 100/10 = 10 A.

Reference: Standard network theory: ac circuit analysis

Question 305

Network TheoryAC Circuit Analysis

Admittance is defined as?

AThe reciprocal of impedance
BThe square of impedance
CResistance plus reactance only
DVoltage divided by power

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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 306

Network TheoryNodal Analysis

A node is connected to ground through a 5 ohm resistor and a 2 A current source injects current into the node. With no other branches, the node voltage is?

A2.5 V
B5 V
C10 V
D20 V

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Correct Answer: C. 10 V

Explanation: By KCL, V/5 = 2 A, so V = 10 V.

Reference: Standard network theory: nodal analysis

Question 307

Network TheoryAC Circuit Analysis

The reciprocal of resistance is called?

AReactance
BConductance
CSusceptance
DInductance

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Correct Answer: B. Conductance

Explanation: Conductance G = 1/R and is measured in siemens.

Reference: Standard network theory: ac circuit analysis

Question 308

Network TheoryMesh Analysis

In mesh analysis, the principal unknown quantities are usually?

ANode voltages
BMesh currents
CCapacitances only
DSource powers only

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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 309

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

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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 310

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

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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 311

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

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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 312

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

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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 313

Network TheoryResonance

The resonant angular frequency of an ideal series RLC circuit is?

AR/L
B1/sqrt(LC)
Csqrt(LC)
D1/(RC)

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Correct Answer: B. 1/sqrt(LC)

Explanation: At resonance XL = XC, giving omega0 = 1/sqrt(LC).

Reference: Standard network theory: resonance

Question 314

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

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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 315

Network TheoryResonance

A series RLC circuit has L = 10 mH and C = 10 microfarad. Its resonant frequency is closest to?

A50.3 Hz
B159 Hz
C503 Hz
D1.59 kHz

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Correct Answer: C. 503 Hz

Explanation: f0 = 1/(2πsqrt(LC)). With L=0.01 H and C=10^-5 F, f0 ≈ 503 Hz.

Reference: Standard network theory: resonance

Question 316

Network TheoryStar-Delta Networks

A balanced star network has each arm equal to 6 ohm. Each resistance of its equivalent balanced delta network is?

A2 ohm
B6 ohm
C12 ohm
D18 ohm

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Correct Answer: D. 18 ohm

Explanation: For a balanced star-to-delta conversion, each delta resistance is 3 times the star resistance: 3×6 = 18 ohm.

Reference: Standard network theory: star-delta networks

Question 317

Network TheoryResonance

At resonance, the impedance of an ideal series RLC circuit reduces to?

AR
BXL
CXC
DInfinite impedance

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Correct Answer: A. R

Explanation: At series resonance XL and XC cancel, leaving the net impedance equal to the resistance R.

Reference: Standard network theory: resonance

Question 318

Network TheoryStar-Delta Networks

A balanced delta network has each resistance equal to 12 ohm. Each arm of its equivalent balanced star network is?

A3 ohm
B4 ohm
C6 ohm
D36 ohm

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Correct Answer: B. 4 ohm

Explanation: For a balanced delta-to-star conversion, each star resistance equals one-third of the delta resistance: 12/3 = 4 ohm.

Reference: Standard network theory: star-delta networks

Question 319

Network TheoryResonance

At series resonance, the power factor of an ideal RLC circuit is?

AZero lagging
BZero leading
CUnity
DAlways 0.5

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Correct Answer: C. Unity

Explanation: At resonance the net reactance is zero, so voltage and current are in phase and power factor is unity.

Reference: Standard network theory: resonance

Question 320

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

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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 321

Network TheoryResonance

A series resonant circuit has resonant frequency 10 kHz and bandwidth 500 Hz. Its quality factor Q is?

A5
B20
C50
D200

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Correct Answer: B. 20

Explanation: For a series resonant circuit, Q = f0/BW = 10000/500 = 20.

Reference: Standard network theory: resonance

Question 322

Network TheoryNetwork Theorems

If a test voltage of 10 V applied to a two-terminal network causes a current of 2 A to enter the network, its equivalent resistance is?

A0.2 ohm
B2 ohm
C5 ohm
D20 ohm

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Correct Answer: C. 5 ohm

Explanation: Req = Vtest/Itest = 10/2 = 5 ohm.

Reference: Standard network theory: network theorems

Question 323

Network TheoryAC Circuit Analysis

The impedance of an ideal inductor in sinusoidal steady state is?

A1/(j omega L)
Bj omega L
CR+jL
Dj/(omega L)

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Correct Answer: B. j omega L

Explanation: An ideal inductor has impedance ZL = j omega L.

Reference: Standard network theory: ac circuit analysis

Question 324

Network TheoryTransient Analysis

An initially uncharged capacitor is connected through a resistor to a DC source V. After one time constant, its voltage is approximately?

A0.368V
B0.5V
C0.632V
DV

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Correct Answer: C. 0.632V

Explanation: For RC charging, vc(t)=V(1-e^(-t/tau)). At t=tau, vc≈V(1-e^-1)=0.632V.

Reference: Standard network theory: transient analysis

Question 325

Network TheorySecond-Order Circuits

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

Aalpha=0
Balpha=omega0
Calpha=2omega0
Domega0=0

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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 326

Network TheoryTransient Analysis

A charged capacitor discharges through a resistor. After one time constant, its voltage is approximately what fraction of its initial value?

A0.368
B0.5
C0.632
D0.865

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Correct Answer: A. 0.368

Explanation: For natural RC discharge, vc(t)=V0e^(-t/tau). At t=tau, vc≈0.368V0.

Reference: Standard network theory: transient analysis

Question 327

Network TheoryTransient Analysis

A series RL circuit with R = 20 ohm and L = 4 H is connected to a DC source. Its time constant is?

A0.05 s
B0.2 s
C5 s
D80 s

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Correct Answer: B. 0.2 s

Explanation: For a series RL circuit, tau=L/R=4/20=0.2 s.

Reference: Standard network theory: transient analysis

Question 328

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

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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 329

Network TheoryLaplace Transform

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

A1
B1/s
Cs
D1/s^2

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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 330

Network TheoryLaplace Transform

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

A1/(s-a)
B1/(s+a)
Cs/(s+a)
Da/(s+a)

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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 331

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

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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 332

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

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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 333

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

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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 334

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

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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 335

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

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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 336

Network TheoryNetwork Functions

A first-order network has transfer function H(s)=1/(s+1000). Its pole is located at?

As=0
Bs=+1000
Cs=-1000
Ds=-1/1000

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Correct Answer: C. s=-1000

Explanation: The pole is the root of s+1000=0, hence s=-1000 rad/s.

Reference: Standard network theory: network functions

Question 337

Network TheoryNetwork Functions

For H(s)=(s+2)/(s+5), the zero and pole are respectively?

A-2 and -5
B-5 and -2
C+2 and +5
D+5 and +2

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Correct Answer: A. -2 and -5

Explanation: The numerator becomes zero at s=-2 and the denominator becomes zero at s=-5.

Reference: Standard network theory: network functions

Question 338

Network TheorySecond-Order Circuits

A series RLC circuit has R = 10 ohm, L = 0.1 H and C = 100 microfarad. Its damping factor alpha = R/(2L) is?

A5 s^-1
B50 s^-1
C100 s^-1
D500 s^-1

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Correct Answer: B. 50 s^-1

Explanation: alpha=R/(2L)=10/(0.2)=50 s^-1.

Reference: Standard network theory: second-order circuits

Question 339

Network TheoryTransient Analysis

Immediately after a switching operation, which quantity of an ideal capacitor cannot change instantaneously?

ACurrent
BVoltage
CPower
DResistance

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Correct Answer: B. Voltage

Explanation: Capacitor voltage cannot change instantaneously because an instantaneous finite voltage change would require an impulse or unbounded current according to i = C dv/dt.

Reference: Standard network theory: transient analysis

Question 340

Network TheorySecond-Order Circuits

For the same RLC circuit with L = 0.1 H and C = 100 microfarad, the undamped natural angular frequency omega0 = 1/sqrt(LC) is?

A100 rad/s
B316.2 rad/s
C1000 rad/s
D3162 rad/s

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Correct Answer: B. 316.2 rad/s

Explanation: LC=0.1×100×10^-6=10^-5, so omega0=1/sqrt(10^-5)≈316.2 rad/s.

Reference: Standard network theory: second-order circuits

Question 341

Network TheoryTransient Analysis

Immediately after a switching operation, which quantity of an ideal inductor cannot change instantaneously?

AVoltage
BCurrent
CResistance
DPower

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Correct Answer: B. Current

Explanation: Inductor current cannot change instantaneously because v = L di/dt; an instantaneous finite current change would require an impulse or unbounded voltage.

Reference: Standard network theory: transient analysis

Question 342

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

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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 343

Network TheoryTwo-Port Networks

For a reciprocal two-port network described by z-parameters, which relation must hold?

Az11=z22 always
Bz12=z21
Cz11=0
Dz12=-z21

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Correct Answer: B. z12=z21

Explanation: A reciprocal two-port has equal transfer impedances: z12=z21.

Reference: Standard network theory: two-port networks

Question 344

Network TheoryTwo-Port Networks

For a symmetrical two-port network described by z-parameters, which relation must hold?

Az11=z22
Bz12=0
Cz21=0
Dz11=-z22

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Correct Answer: A. z11=z22

Explanation: For a symmetrical two-port, interchanging input and output ports does not change its behavior, giving z11=z22.

Reference: Standard network theory: two-port networks

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

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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

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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

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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 348

Network TheoryTwo-Port Networks

A reciprocal two-port network described by ABCD parameters satisfies which condition?

AA+D=0
BAD-BC=1
CAB-CD=0
DA=B=C=D

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Correct Answer: B. AD-BC=1

Explanation: With the standard transmission-parameter convention, reciprocity requires the determinant AD-BC to equal 1.

Reference: Standard network theory: two-port networks

Question 349

Network TheoryThree-Phase Circuits

In a balanced three-phase delta-connected load, the relation between line current IL and phase current Iph is?

AIL=Iph
BIL=√3 Iph
CIL=3Iph
DIL=Iph/√3

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Correct Answer: B. IL=√3 Iph

Explanation: For a balanced delta connection, line current magnitude is √3 times phase current magnitude.

Reference: Standard network theory: three-phase circuits

Question 350

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)

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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 351

Network TheoryThree-Phase Circuits

A balanced three-phase load operates at VL = 400 V, IL = 10 A and unity power factor. Its total real power is closest to?

A2.31 kW
B4.00 kW
C6.93 kW
D12.0 kW

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Correct Answer: C. 6.93 kW

Explanation: P=√3×400×10×1 ≈ 6928 W = 6.93 kW.

Reference: Standard network theory: three-phase circuits

Question 352

Network TheoryLaplace Transform

The initial-value theorem for a function f(t) is commonly written, when applicable, as f(0+) =?

Alim s->0 sF(s)
Blim s->infinity sF(s)
Clim s->infinity F(s)/s
DF(0)

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Correct Answer: B. lim s->infinity sF(s)

Explanation: The initial-value theorem gives f(0+) = lim as s approaches infinity of sF(s), subject to its applicability conditions.

Reference: Standard network theory: laplace transform

Question 353

Network TheoryLaplace Transform

The final-value theorem is commonly written, when applicable, as f(infinity) =?

Alim s->0 sF(s)
Blim s->infinity sF(s)
Clim s->0 F(s)/s
DF(infinity) directly

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Correct Answer: A. lim s->0 sF(s)

Explanation: The final-value theorem gives lim t->infinity f(t)=lim s->0 sF(s), provided the required pole conditions are satisfied.

Reference: Standard network theory: laplace transform

Question 354

Network TheoryLaplace Transform

For F(s)=10/[s(s+2)], the final value of f(t), assuming the final-value theorem applies, is?

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Correct Answer: C. 5

Explanation: lim s->0 sF(s)=lim s->0 10/(s+2)=5.

Reference: Standard network theory: laplace transform

Question 355

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)

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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 356

Network TheoryResonance

A series RLC circuit has R = 20 ohm, L = 0.2 H and C = 50 microfarad. Its resonant frequency is closest to?

A15.9 Hz
B50.3 Hz
C159 Hz
D503 Hz

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Correct Answer: B. 50.3 Hz

Explanation: f0 = 1/(2π√LC). Here LC = 0.2×50×10^-6 = 10^-5, so f0 ≈ 50.3 Hz.

Reference: Standard network theory: resonance

Question 357

Network TheoryNetwork Functions

For a causal system with transfer function H(s)=10/(s+10), the DC gain H(0) is?

A0
B1
C10
D100

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Correct Answer: B. 1

Explanation: H(0)=10/(0+10)=1.

Reference: Standard network theory: network functions

Question 358

Network TheoryResonance

For the same series RLC circuit with R = 20 ohm, L = 0.2 H and C = 50 microfarad, its quality factor Q = omega0 L/R is closest to?

A0.316
B1.0
C3.16
D31.6

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Correct Answer: C. 3.16

Explanation: omega0 = 1/√LC ≈ 316.2 rad/s. Therefore Q = 316.2×0.2/20 ≈ 3.16.

Reference: Standard network theory: resonance

Question 359

Network TheoryNetwork Functions

A transfer function has poles at s=-2 and s=-5. Which pole is dominant in the usual time-response sense?

As=-5
Bs=-2
CBoth are always equally dominant
DNeither pole affects response

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Correct Answer: B. s=-2

Explanation: The pole closer to the imaginary axis, s=-2, corresponds to the slower decaying exponential and generally dominates the long-term transient.

Reference: Standard network theory: network functions

Question 360

Network TheoryResonance

A series RLC circuit has R = 10 ohm and L = 0.1 H. Its bandwidth in rad/s is R/L, equal to?

A10 rad/s
B100 rad/s
C1000 rad/s
D10000 rad/s

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Correct Answer: B. 100 rad/s

Explanation: For a series RLC circuit, bandwidth in angular frequency is Δomega = R/L = 10/0.1 = 100 rad/s.

Reference: Standard network theory: resonance

Question 361

Network TheoryNetwork Functions

A first-order network has a pole at s=-200 rad/s. Its time constant is?

A0.5 ms
B5 ms
C20 ms
D200 ms

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Correct Answer: B. 5 ms

Explanation: For a first-order pole at -1/tau, tau=1/200 s=0.005 s=5 ms.

Reference: Standard network theory: network functions

Question 362

Network TheoryResonance

At parallel resonance in an ideal parallel RLC circuit, the input impedance is ideally?

AMinimum and zero
BMaximum
CEqual to inductive reactance only
DAlways 1 ohm

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Correct Answer: B. Maximum

Explanation: At parallel resonance the reactive branch currents cancel at the input, making the input admittance minimum and impedance maximum in the ideal case.

Reference: Standard network theory: resonance

Question 363

Network TheorySecond-Order Circuits

A second-order characteristic equation is s^2 + 6s + 25 = 0. Comparing with s^2 + 2 zeta omega_n s + omega_n^2, the natural frequency omega_n is?

A5 rad/s
B6 rad/s
C12.5 rad/s
D25 rad/s

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Correct Answer: A. 5 rad/s

Explanation: omega_n^2=25, so omega_n=5 rad/s.

Reference: Standard network theory: second-order circuits

Question 364

Network TheoryAC Power

A coil has resistance 6 ohm and inductive reactance 8 ohm. Its impedance magnitude and power factor are respectively?

A10 ohm and 0.6
B14 ohm and 0.8
C10 ohm and 0.8
D2 ohm and 0.6

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Correct Answer: A. 10 ohm and 0.6

Explanation: |Z|=√(6^2+8^2)=10 ohm. Power factor = R/|Z| = 6/10 = 0.6 lagging.

Reference: Standard network theory: ac power

Question 365

Network TheorySecond-Order Circuits

For s^2 + 6s + 25 = 0, the damping ratio zeta is?

A0.3
B0.6
C1.2
D5

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Correct Answer: B. 0.6

Explanation: 2 zeta omega_n=6 and omega_n=5, so zeta=6/(2×5)=0.6.

Reference: Standard network theory: second-order circuits

Question 366

Network TheoryAC Power

A load consumes 800 W at a power factor of 0.8 lagging. Its apparent power is?

A640 VA
B800 VA
C1000 VA
D1250 VA

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Correct Answer: C. 1000 VA

Explanation: Apparent power S = P/pf = 800/0.8 = 1000 VA.

Reference: Standard network theory: ac power

Question 367

Network TheorySecond-Order Circuits

A second-order network with damping ratio zeta = 0.6 is?

AUndamped
BUnderdamped
CCritically damped
DOverdamped

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Correct Answer: B. Underdamped

Explanation: A second-order system is underdamped when 0<zeta<1.

Reference: Standard network theory: second-order circuits

Question 368

Network TheoryAC Power

A load has apparent power 1000 VA and real power 600 W. The magnitude of reactive power is?

A400 var
B600 var
C800 var
D1600 var

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Correct Answer: C. 800 var

Explanation: Using S^2=P^2+Q^2, Q=√(1000^2-600^2)=800 var.

Reference: Standard network theory: ac power

Question 369

Network TheoryTwo-Port Networks

For a reciprocal two-port network represented by ABCD parameters, the determinant condition is?

AAD+BC=1
BAD-BC=1
CA+D=1
DB=C=0

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Correct Answer: B. AD-BC=1

Explanation: Using the standard transmission-parameter convention, reciprocity requires AD-BC=1.

Reference: Standard network theory: two-port networks

Question 370

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

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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 371

Network TheoryTwo-Port Networks

For a symmetrical two-port network represented by ABCD parameters, which relation holds?

AA=D
BB=C always
CA=0
DD=0

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Correct Answer: A. A=D

Explanation: For a symmetrical two-port, the transmission parameters satisfy A=D.

Reference: Standard network theory: two-port networks

Question 372

Network TheoryThree-Phase Circuits

In a balanced three-phase star-connected load, the relation between line voltage VL and phase voltage Vph is?

AVL=Vph
BVL=√3 Vph
CVL=3Vph
DVL=Vph/√3

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Correct Answer: B. VL=√3 Vph

Explanation: For a balanced star connection, line voltage magnitude is √3 times phase voltage magnitude.

Reference: Standard network theory: three-phase circuits

Question 373

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

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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 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

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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

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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 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

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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 377

Communication SystemsCommunication Fundamentals

If a sinusoidal carrier has frequency 1 MHz, its period is?

A1 ns
B0.1 microsecond
C1 microsecond
D1 millisecond

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Correct Answer: C. 1 microsecond

Explanation: T=1/f=1/(10^6)=1 microsecond.

Reference: Standard communication systems: communication fundamentals

Question 378

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

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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 379

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

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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 380

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

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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 381

Communication SystemsAngle Modulation

In frequency modulation, which parameter of the carrier is varied according to the message?

AAmplitude
BInstantaneous frequency
CAverage power only
DAntenna resistance

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Correct Answer: B. Instantaneous frequency

Explanation: FM varies the instantaneous carrier frequency according to the message while ideally keeping amplitude constant.

Reference: Standard communication systems: angle modulation

Question 382

Communication SystemsAmplitude Modulation

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

AAmplitude
BFrequency
CPhase only
DPropagation velocity

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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 383

Communication SystemsAngle Modulation

In phase modulation, which carrier parameter is directly varied according to the message?

AAmplitude
BPhase
CAverage DC value
DPropagation speed

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Correct Answer: B. Phase

Explanation: PM varies the instantaneous phase of the carrier in accordance with the modulating signal.

Reference: Standard communication systems: angle modulation

Question 384

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

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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 385

Communication SystemsFrequency Modulation

An FM signal has peak frequency deviation 75 kHz and maximum modulating frequency 15 kHz. Its modulation index beta is?

A0.2
B5
C15
D90

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Correct Answer: B. 5

Explanation: For FM, beta=Delta f/fm=75/15=5.

Reference: Standard communication systems: frequency modulation

Question 386

Communication SystemsAmplitude Modulation

An AM signal has carrier amplitude 10 V and modulating-signal amplitude 5 V. Its modulation index is?

A0.25
B0.5
C1.0
D2.0

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Correct Answer: B. 0.5

Explanation: m=Am/Ac=5/10=0.5, corresponding to 50% modulation.

Reference: Standard communication systems: amplitude modulation

Question 387

Communication SystemsFrequency Modulation

Using Carson’s rule, the approximate bandwidth of an FM signal with peak deviation 75 kHz and maximum modulating frequency 15 kHz is?

A90 kHz
B150 kHz
C180 kHz
D300 kHz

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Correct Answer: C. 180 kHz

Explanation: Carson's rule gives B≈2(Delta f+fm)=2(75+15)=180 kHz.

Reference: Standard communication systems: frequency modulation

Question 388

Communication SystemsAmplitude Modulation

For distortion-free conventional AM with a sinusoidal message, the modulation index should normally not exceed?

A0.1
B0.5
C1
D2

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Correct Answer: C. 1

Explanation: When m exceeds 1, overmodulation causes envelope distortion in conventional AM.

Reference: Standard communication systems: amplitude modulation

Question 389

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

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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 390

Communication SystemsAmplitude Modulation

A carrier of 1 MHz is amplitude-modulated by a 5 kHz sinusoid. The upper sideband frequency is?

A995 kHz
B1.000 MHz
C1.005 MHz
D1.500 MHz

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Correct Answer: C. 1.005 MHz

Explanation: The upper sideband is fc+fm=1000 kHz+5 kHz=1005 kHz=1.005 MHz.

Reference: Standard communication systems: amplitude modulation

Question 391

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%

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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

Question 392

Communication SystemsAmplitude Modulation

For the same 1 MHz carrier modulated by 5 kHz, the lower sideband frequency is?

A995 kHz
B1.005 MHz
C1.050 MHz
D5 kHz

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Correct Answer: A. 995 kHz

Explanation: The lower sideband is fc-fm=1000 kHz-5 kHz=995 kHz.

Reference: Standard communication systems: amplitude modulation

Question 393

Communication SystemsAmplitude Modulation

The bandwidth of a conventional AM signal whose highest modulating frequency is 5 kHz is?

A2.5 kHz
B5 kHz
C10 kHz
D1 MHz

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Correct Answer: C. 10 kHz

Explanation: Conventional AM contains upper and lower sidebands, so bandwidth B=2fm(max)=10 kHz.

Reference: Standard communication systems: amplitude modulation

Question 394

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

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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 395

Communication SystemsAmplitude Modulation

For a conventional AM signal with modulation index m=1, the total transmitted power relative to carrier power Pc is?

APc
B1.25Pc
C1.5Pc
D2Pc

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Correct Answer: C. 1.5Pc

Explanation: For single-tone AM, Pt=Pc(1+m^2/2). At m=1, Pt=1.5Pc.

Reference: Standard communication systems: amplitude modulation

Question 396

Communication SystemsDSB-SC & SSB

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

ABoth sidebands
BCarrier
CMessage signal
DReceiver local oscillator

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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 397

Communication SystemsDSB-SC & SSB

Compared with conventional AM, DSB-SC mainly saves transmitted power by eliminating the?

AUpper sideband
BLower sideband
CCarrier
DMessage bandwidth

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Correct Answer: C. Carrier

Explanation: The conventional AM carrier consumes substantial power but carries no information by itself, so suppressing it improves power efficiency.

Reference: Standard communication systems: dsb-sc & ssb

Question 398

Communication SystemsDSB-SC & SSB

The ideal bandwidth of an SSB signal carrying a baseband message of bandwidth 3 kHz is?

A1.5 kHz
B3 kHz
C6 kHz
D12 kHz

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Correct Answer: B. 3 kHz

Explanation: Single-sideband transmission sends only one sideband, so its transmission bandwidth equals the message bandwidth.

Reference: Standard communication systems: dsb-sc & ssb

Question 399

Communication SystemsSampling

According to the sampling theorem, a band-limited signal with maximum frequency fm should ideally be sampled at a rate of at least?

Afm/2
Bfm
C2fm
D4fm only

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Correct Answer: C. 2fm

Explanation: The Nyquist sampling criterion requires fs to be at least 2fm for a signal band-limited to fm, under ideal conditions.

Reference: Standard communication systems: sampling

Question 400

Communication SystemsSampling

A baseband signal contains frequencies up to 5 kHz. Its Nyquist rate is?

A2.5 kHz
B5 kHz
C10 kHz
D20 kHz

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Correct Answer: C. 10 kHz

Explanation: Nyquist rate = 2fm = 2×5 kHz = 10 kHz.

Reference: Standard communication systems: sampling