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NTPC MCQs

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

Question 904
Electromagnetic TheoryBiot-Savart Law

The Biot-Savart law is used to calculate magnetic field produced by?

  • ACurrent elements
  • BStationary electric charges only
  • CDielectric polarization only
  • DScalar potential without current
Report an error
Correct Answer: A. Current elements
Explanation: Biot-Savart law gives the magnetic field contribution from electric current elements.
Reference: Standard electromagnetic theory: biot-savart law
Question 905
Electromagnetic TheoryPotential Equations

In a charge-free region with uniform permittivity, the electrostatic potential V satisfies?

  • ALaplace's equation
  • BPoisson's equation with nonzero charge density
  • CWave equation only
  • DContinuity equation only
Report an error
Correct Answer: A. Laplace's equation
Explanation: When volume charge density is zero, Poisson's equation reduces to Laplace's equation, ∇²V=0.
Reference: Standard electromagnetic theory: potential equations
Question 907
Electromagnetic TheoryBoundary Conditions

At the boundary between two perfect dielectric media with no free surface charge, which component of electric flux density D is continuous?

  • ANormal component
  • BTangential component only
  • CBoth components must be zero
  • DNeither component
Report an error
Correct Answer: A. Normal component
Explanation: The boundary condition is D1n-D2n=ρs. With no free surface charge, the normal components are equal.
Reference: Standard electromagnetic theory: boundary conditions
Question 911
Electromagnetic TheoryCurrent Density

The SI unit of current density J is?

  • AA/m²
  • BA/m
  • CC/m²
  • DV/m²
Report an error
Correct Answer: A. A/m²
Explanation: Current density is electric current per unit cross-sectional area, measured in amperes per square metre.
Reference: Standard electromagnetic theory: current density
Question 913
Electromagnetic TheoryContinuity Equation

The general differential form of the charge continuity equation is?

  • A∇·J = -partial rho_v/partial t
  • B∇×J = -partial rho_v/partial t
  • C∇·J = rho_v
  • D∇×E = J
Report an error
Correct Answer: A. ∇·J = -partial rho_v/partial t
Explanation: Charge conservation is expressed locally by ∇·J=-∂ρv/∂t.
Reference: Standard electromagnetic theory: continuity equation
Question 914
Electromagnetic TheoryContinuity Equation

For steady current conditions, the continuity equation reduces to?

  • A∇·J = 0
  • B∇×J = 0 always
  • CJ = 0
  • D∇·D = 0 in every conductor
Report an error
Correct Answer: A. ∇·J = 0
Explanation: Under steady conditions charge density does not change with time, so ∇·J=0.
Reference: Standard electromagnetic theory: continuity equation
Question 915
Electromagnetic TheoryMagnetostatics

The magnetic flux density B is measured in?

  • ATesla
  • BWeber per metre
  • CAmpere per metre
  • DHenry
Report an error
Correct Answer: A. Tesla
Explanation: The SI unit of magnetic flux density is tesla (T), equivalent to Wb/m².
Reference: Standard electromagnetic theory: magnetostatics
Question 916
Electromagnetic TheoryMagnetostatics

The magnetic field intensity H is measured in?

  • AA/m
  • BTesla
  • CWeber
  • DC/m²
Report an error
Correct Answer: A. A/m
Explanation: Magnetic field intensity H has SI unit ampere per metre.
Reference: Standard electromagnetic theory: magnetostatics
Question 918
Electromagnetic TheoryMagnetic Field

The direction of magnetic field around a long straight current-carrying conductor is determined by the?

  • ARight-hand rule
  • BLeft-hand electrostatic rule
  • CLenz law only
  • DGauss electric law only
Report an error
Correct Answer: A. Right-hand rule
Explanation: Curling the fingers of the right hand around the conductor with the thumb along current gives the magnetic-field direction.
Reference: Standard electromagnetic theory: magnetic field
Question 923
Electromagnetic TheoryMaxwell Equations Basics

The differential form of Gauss’s law for magnetism is?

  • A∇·B = 0
  • B∇×B = 0 always
  • C∇·B = rho_v
  • D∇×B = -partial D/partial t
Report an error
Correct Answer: A. ∇·B = 0
Explanation: The magnetic flux density is divergence-free: ∇·B=0.
Reference: Standard electromagnetic theory: maxwell equations basics
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Question 932
Electromagnetic TheoryInductance

The SI unit of inductance is?

  • AHenry
  • BTesla
  • CWeber per square metre
  • DFarad
Report an error
Correct Answer: A. Henry
Explanation: Inductance is measured in henries (H).
Reference: Standard electromagnetic theory: inductance
Question 933
Electromagnetic TheoryInductance

The voltage across an ideal inductor of constant inductance L is?

  • Av = L di/dt
  • Bv = i/L
  • Cv = Li
  • Dv = L/i
Report an error
Correct Answer: A. v = L di/dt
Explanation: For a constant linear inductance, the induced terminal voltage is proportional to the rate of change of current: v=L di/dt.
Reference: Standard electromagnetic theory: inductance
Question 937
Electromagnetic TheoryFaraday's Law

Faraday’s law states that the induced emf around a closed path is equal to?

  • AThe negative time rate of change of magnetic flux linkage
  • BThe magnetic flux itself
  • CThe electric charge enclosed
  • DThe resistance multiplied by magnetic field
Report an error
Correct Answer: A. The negative time rate of change of magnetic flux linkage
Explanation: Faraday's law gives induced emf as the negative time derivative of magnetic flux linkage.
Reference: Standard electromagnetic theory: faraday's law
Question 938
Electromagnetic TheoryFaraday's Law

The negative sign in Faraday’s law is associated with?

  • ALenz's law
  • BCoulomb's law
  • CGauss's electric law
  • DOhm's law
Report an error
Correct Answer: A. Lenz's law
Explanation: The negative sign expresses Lenz's law: the induced effect opposes the change in magnetic flux that produces it.
Reference: Standard electromagnetic theory: faraday's law
Question 940
Electromagnetic TheoryFaraday's Law

A stationary closed conducting loop is placed in a magnetic field that is constant with time. If the flux through the loop does not change, the transformer-induced emf is?

  • AZero
  • BMaximum
  • CEqual to magnetic flux
  • DAlways 1 V
Report an error
Correct Answer: A. Zero
Explanation: Faraday's law requires a time-varying flux linkage for transformer emf; if flux is constant, induced emf is zero.
Reference: Standard electromagnetic theory: faraday's law
Question 944
Electromagnetic TheoryEM Wave Fundamentals

The intrinsic impedance of free space is approximately?

  • A50 ohm
  • B75 ohm
  • C120 pi ohm
  • D600 ohm
Report an error
Correct Answer: C. 120 pi ohm
Explanation: η0=sqrt(mu0/epsilon0)=120π ohm, approximately 377 ohm.
Reference: Standard electromagnetic theory: em wave fundamentals
Question 946
Electromagnetic TheoryMutual Inductance

Mutual inductance describes the magnetic coupling between?

  • ATwo circuits or coils
  • BOnly two capacitors
  • CA resistor and a battery only
  • DTwo isolated static charges
Report an error
Correct Answer: A. Two circuits or coils
Explanation: Mutual inductance quantifies how changing current in one circuit induces emf in another magnetically coupled circuit.
Reference: Standard electromagnetic theory: mutual inductance
Question 949
Electromagnetic TheoryMaxwell Equations

Maxwell introduced displacement current primarily to extend which law to time-varying fields?

  • AAmpere's circuital law
  • BCoulomb's law
  • CGauss's magnetic law
  • DBiot-Savart law for static point charges
Report an error
Correct Answer: A. Ampere's circuital law
Explanation: The displacement-current term makes Ampere's law consistent with charge conservation in time-varying electromagnetic fields.
Reference: Standard electromagnetic theory: maxwell equations
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Question 951
Electromagnetic TheoryMaxwell Equations

The Maxwell-Ampere equation in differential form is?

  • Acurl H = J + partial D/partial t
  • Bcurl E = J + partial D/partial t
  • Cdiv H = J
  • Ddiv D = J + partial B/partial t
Report an error
Correct Answer: A. curl H = J + partial D/partial t
Explanation: Maxwell-Ampere law is ∇×H=J+∂D/∂t.
Reference: Standard electromagnetic theory: maxwell equations
Question 952
Electromagnetic TheoryMaxwell Equations

Faraday’s law in differential form is?

  • Acurl E = -partial B/partial t
  • Bdiv E = -partial B/partial t
  • Ccurl H = -partial B/partial t
  • Ddiv B = -partial E/partial t
Report an error
Correct Answer: A. curl E = -partial B/partial t
Explanation: The differential Faraday law is ∇×E=-∂B/∂t.
Reference: Standard electromagnetic theory: maxwell equations
Question 953
Electromagnetic TheoryEM Wave Fundamentals

In a source-free lossless homogeneous medium, electromagnetic waves are?

  • ATransverse, with E and H perpendicular to the direction of propagation
  • BPurely longitudinal with E parallel to propagation
  • CPurely electrostatic
  • DUnable to carry energy
Report an error
Correct Answer: A. Transverse, with E and H perpendicular to the direction of propagation
Explanation: Uniform plane electromagnetic waves in a source-free isotropic medium have mutually perpendicular E, H and propagation directions.
Reference: Standard electromagnetic theory: em wave fundamentals
Question 954
Electromagnetic TheoryPoynting Vector

The Poynting vector represents electromagnetic?

  • APower-flow density
  • BCharge density
  • CMagnetic reluctance
  • DElectric potential
Report an error
Correct Answer: A. Power-flow density
Explanation: The Poynting vector S=E×H gives electromagnetic power flow per unit area.
Reference: Standard electromagnetic theory: poynting vector
Question 955
Electromagnetic TheorySkin Effect

For a good conductor, the skin depth is approximately?

  • Asqrt(2/(omega mu sigma))
  • Bsqrt(omega mu sigma/2)
  • Comega mu sigma
  • D2 omega/(mu sigma)
Report an error
Correct Answer: A. sqrt(2/(omega mu sigma))
Explanation: The standard good-conductor approximation is δ=sqrt(2/(ωμσ)).
Reference: Standard electromagnetic theory: skin effect
Question 956
Electromagnetic TheoryReflection & Transmission

The reflection coefficient for electric-field amplitude at normal incidence is defined as?

  • AReflected electric-field amplitude divided by incident electric-field amplitude
  • BIncident field divided by reflected field
  • CTransmitted power divided by incident power only
  • DReflected magnetic field multiplied by incident field
Report an error
Correct Answer: A. Reflected electric-field amplitude divided by incident electric-field amplitude
Explanation: The electric-field reflection coefficient is Γ=Er/Ei at the interface.
Reference: Standard electromagnetic theory: reflection & transmission
Question 957
Electromagnetic TheoryReflection & Transmission

If a wave is incident normally from a medium of intrinsic impedance eta1 onto a medium of impedance eta2, the electric-field reflection coefficient is?

  • A(eta2-eta1)/(eta2+eta1)
  • B(eta2+eta1)/(eta2-eta1)
  • Ceta1/eta2
  • Deta1+eta2
Report an error
Correct Answer: A. (eta2-eta1)/(eta2+eta1)
Explanation: Applying tangential E and H boundary conditions gives Γ=(η2-η1)/(η2+η1).
Reference: Standard electromagnetic theory: reflection & transmission
Question 960
Electromagnetic TheoryStanding Waves

A standing wave is produced by the superposition of?

  • AIncident and reflected waves traveling in opposite directions
  • BTwo DC electric fields only
  • COnly one traveling wave
  • DTwo unrelated static magnetic fields
Report an error
Correct Answer: A. Incident and reflected waves traveling in opposite directions
Explanation: Interference between forward and reflected waves of the same frequency creates a standing-wave pattern.
Reference: Standard electromagnetic theory: standing waves
Question 961
Electromagnetic TheoryPoynting Vector

The SI unit of the Poynting vector is?

  • AW/m²
  • BJ/m
  • CV/m
  • DA/m²
Report an error
Correct Answer: A. W/m²
Explanation: Because the Poynting vector is power per unit area, its SI unit is watt per square metre.
Reference: Standard electromagnetic theory: poynting vector
Question 965
Electromagnetic TheoryWave Propagation

The complex propagation constant gamma is conventionally written as?

  • Aalpha + j beta
  • Bbeta + j alpha only
  • Calpha beta
  • Dj(alpha + beta)
Report an error
Correct Answer: A. alpha + j beta
Explanation: The propagation constant is γ=α+jβ, where α is attenuation constant and β is phase constant.
Reference: Standard electromagnetic theory: wave propagation
Question 966
Electromagnetic TheoryStanding Waves

A VSWR of 1 corresponds to?

  • APerfect matching with no reflection
  • BTotal reflection
  • CA reflection coefficient magnitude of 1
  • DInfinite attenuation
Report an error
Correct Answer: A. Perfect matching with no reflection
Explanation: VSWR=1 occurs only when |Γ|=0, corresponding to a matched condition.
Reference: Standard electromagnetic theory: standing waves
Question 967
Electromagnetic TheoryWave Propagation

The attenuation constant alpha is commonly measured in?

  • ANp/m
  • Brad/m
  • CHz/m
  • DWb/m
Report an error
Correct Answer: A. Np/m
Explanation: The attenuation constant describes exponential amplitude decay and is measured in nepers per metre.
Reference: Standard electromagnetic theory: wave propagation
Question 968
Electromagnetic TheoryPolarization

The polarization of an electromagnetic wave is specified by the behavior of its?

  • AElectric-field vector
  • BPropagation speed only
  • CMagnetic permeability only
  • DFrequency counter reading
Report an error
Correct Answer: A. Electric-field vector
Explanation: Wave polarization is conventionally defined by the locus and orientation of the electric-field vector at a fixed point.
Reference: Standard electromagnetic theory: polarization
Question 969
Electromagnetic TheoryWave Propagation

The phase constant beta is commonly measured in?

  • Arad/m
  • BNp/m
  • CS/m
  • DC/m
Report an error
Correct Answer: A. rad/m
Explanation: The phase constant describes phase change per unit distance and is measured in radians per metre.
Reference: Standard electromagnetic theory: wave propagation
Question 971
Electromagnetic TheoryWave Propagation

The phase constant beta and wavelength lambda are related by?

  • Abeta = 2 pi/lambda
  • Bbeta = lambda/(2 pi)
  • Cbeta = 2 pi lambda
  • Dbeta = 1/lambda²
Report an error
Correct Answer: A. beta = 2 pi/lambda
Explanation: A phase change of 2π radians occurs over one wavelength, hence β=2π/λ.
Reference: Standard electromagnetic theory: wave propagation
Question 973
Electromagnetic TheorySkin Effect

Skin effect causes high-frequency current in a good conductor to concentrate mainly?

  • ANear the conductor surface
  • BUniformly throughout the entire cross-section
  • COnly at the conductor axis
  • DOutside the conductor with zero internal current
Report an error
Correct Answer: A. Near the conductor surface
Explanation: At higher frequency, electromagnetic diffusion causes current density to become concentrated near the surface.
Reference: Standard electromagnetic theory: skin effect
Question 974
Electromagnetic TheorySkin Effect

For a good conductor, skin depth decreases when frequency?

  • AIncreases
  • BDecreases
  • CBecomes zero only
  • DHas no effect
Report an error
Correct Answer: A. Increases
Explanation: For a good conductor, δ≈sqrt(2/(omega mu sigma)), so increasing frequency decreases skin depth.
Reference: Standard electromagnetic theory: skin effect
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Question 977
Electromagnetic TheoryPolarization

Two orthogonal field components generally produce elliptical polarization when they have?

  • ASuitable unequal amplitudes and/or a phase difference other than the special linear/circular cases
  • BZero frequency only
  • CNo electric field
  • DOnly identical phase and identical direction
Report an error
Correct Answer: A. Suitable unequal amplitudes and/or a phase difference other than the special linear/circular cases
Explanation: Elliptical polarization is the general case for orthogonal components with relative amplitude and phase that do not reduce to linear or circular polarization.
Reference: Standard electromagnetic theory: polarization
Question 979
Antenna & Wave PropagationRadiation Pattern

The radiation pattern of an antenna describes the variation of its radiation properties with?

  • ADirection in space
  • BSupply voltage only
  • CConductor resistance only
  • DTime of day
Report an error
Correct Answer: A. Direction in space
Explanation: An antenna radiation pattern shows how radiation intensity, field strength or related quantities vary with direction.
Reference: Standard antenna and wave propagation: radiation pattern
Question 982
Antenna & Wave PropagationRadiation Pattern

A lobe other than the major lobe is generally called a?

  • AMinor lobe
  • BIsotropic lobe
  • CFeed lobe
  • DImpedance lobe
Report an error
Correct Answer: A. Minor lobe
Explanation: Side lobes and back lobes are collectively minor lobes because they are not the principal radiation lobe.
Reference: Standard antenna and wave propagation: radiation pattern
Question 983
Antenna & Wave PropagationIsotropic Radiator

An isotropic radiator is a hypothetical antenna that radiates?

  • AEqually in all directions
  • BOnly along one axis
  • COnly in the horizontal plane
  • DNo power
Report an error
Correct Answer: A. Equally in all directions
Explanation: An isotropic radiator is an ideal reference source with uniform radiation intensity in every direction.
Reference: Standard antenna and wave propagation: isotropic radiator
Question 984
Antenna & Wave PropagationDirectivity & Gain

The directivity of an isotropic radiator is?

  • A1 or 0 dBi
  • B2 or 3 dBi
  • C1.64 or 2.15 dBi
  • DInfinite
Report an error
Correct Answer: A. 1 or 0 dBi
Explanation: By definition, an isotropic radiator has directivity 1, corresponding to 0 dBi.
Reference: Standard antenna and wave propagation: directivity & gain
Question 985
Antenna & Wave PropagationDirectivity & Gain

Antenna directivity is the ratio of radiation intensity in a specified direction to?

  • AAverage radiation intensity over all directions
  • BInput current only
  • COhmic resistance
  • DWavelength squared only
Report an error
Correct Answer: A. Average radiation intensity over all directions
Explanation: Directivity compares radiation intensity in a given direction, usually its maximum, with the average radiation intensity.
Reference: Standard antenna and wave propagation: directivity & gain
Question 986
Antenna & Wave PropagationDirectivity & Gain

Antenna gain differs from directivity because gain also accounts for?

  • AAntenna efficiency
  • BOnly operating frequency
  • COnly polarization direction
  • DSpeed of light
Report an error
Correct Answer: A. Antenna efficiency
Explanation: Gain includes the effect of radiation efficiency, whereas directivity is based on the shape of the radiation pattern.
Reference: Standard antenna and wave propagation: directivity & gain
Question 988
Antenna & Wave PropagationDirectivity & Gain

A power gain of 10 corresponds to approximately?

  • A3 dB
  • B10 dB
  • C20 dB
  • D100 dB
Report an error
Correct Answer: B. 10 dB
Explanation: Gain in decibels is 10log10(10)=10 dB.
Reference: Standard antenna and wave propagation: directivity & gain
Question 990
Antenna & Wave PropagationAntenna Fundamentals

The primary function of a transmitting antenna is to convert?

  • AGuided electromagnetic energy into radiated electromagnetic waves
  • BDC power directly into mechanical energy
  • CSound waves into heat only
  • DDigital data into resistance
Report an error
Correct Answer: A. Guided electromagnetic energy into radiated electromagnetic waves
Explanation: A transmitting antenna couples guided RF energy from a transmission system into electromagnetic waves that propagate through space.
Reference: Standard antenna and wave propagation: antenna fundamentals
Question 991
Antenna & Wave PropagationAntenna Fundamentals

A receiving antenna primarily converts incident electromagnetic waves into?

  • AElectrical signals available at its terminals
  • BMechanical rotation only
  • CDC resistance only
  • DOptical energy only
Report an error
Correct Answer: A. Electrical signals available at its terminals
Explanation: A receiving antenna intercepts electromagnetic energy and produces a corresponding electrical signal at its terminals.
Reference: Standard antenna and wave propagation: antenna fundamentals
Question 992
Antenna & Wave PropagationAntenna Impedance

For maximum power transfer between a transmission line and an antenna at a single frequency, the antenna input impedance should ideally be?

  • AMatched to the line impedance
  • BZero
  • CInfinite
  • DPurely capacitive regardless of the line
Report an error
Correct Answer: A. Matched to the line impedance
Explanation: Impedance matching minimizes reflection and permits efficient transfer of power from the line to the antenna.
Reference: Standard antenna and wave propagation: antenna impedance
Question 993
Antenna & Wave PropagationPolarization

The polarization of an antenna is normally defined by the polarization of the wave it?

  • ARadiates in a specified direction
  • BAbsorbs as heat only
  • CReflects from the ground only
  • DCarries inside a DC cable
Report an error
Correct Answer: A. Radiates in a specified direction
Explanation: Antenna polarization is described by the electric-field polarization of its radiated wave in the direction considered.
Reference: Standard antenna and wave propagation: polarization
Question 994
Antenna & Wave PropagationDipole Antennas

A vertically oriented half-wave dipole ideally produces what polarization in its broadside direction?

  • AVertical linear polarization
  • BHorizontal linear polarization
  • CCircular polarization automatically
  • DUnpolarized radiation
Report an error
Correct Answer: A. Vertical linear polarization
Explanation: The electric field of a thin dipole is oriented parallel to the dipole axis, giving vertical linear polarization for a vertical dipole.
Reference: Standard antenna and wave propagation: dipole antennas
Question 1000
Antenna & Wave PropagationBeamwidth

A narrower main beam generally indicates?

  • AHigher directivity
  • BLower directivity in every case
  • CZero gain
  • DNo radiation
Report an error
Correct Answer: A. Higher directivity
Explanation: Concentrating radiation into a narrower angular region generally increases antenna directivity.
Reference: Standard antenna and wave propagation: beamwidth
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