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RRB MCQs

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

Question 903
Electromagnetic TheoryElectric Field

The SI unit of electric field intensity E is?

  • AV/m
  • BWb/m²
  • CA/m
  • DC/m² only
Report an error
Correct Answer: A. V/m
Explanation: Electric field intensity is measured in N/C, equivalently V/m.
Reference: Standard electromagnetic theory: electric field
Question 906
Electromagnetic TheoryElectric Potential

The SI unit of electric potential is?

  • AVolt
  • BTesla
  • CHenry
  • DFarad per metre
Report an error
Correct Answer: A. Volt
Explanation: Electric potential is measured in volts.
Reference: Standard electromagnetic theory: electric potential
Question 907
Electromagnetic TheoryElectric Potential

Electric field and electric potential are related by?

  • AE = -grad V
  • BE = grad V without a minus sign
  • CE = V²
  • DE = div V
Report an error
Correct Answer: A. E = -grad V
Explanation: The electric field equals the negative gradient of potential.
Reference: Standard electromagnetic theory: electric potential
Question 908
Electromagnetic TheoryElectric Potential

An equipotential surface is a surface on which?

  • AElectric potential is constant
  • BElectric field is always zero everywhere
  • CCharge density is necessarily zero
  • DMagnetic flux is constant by definition
Report an error
Correct Answer: A. Electric potential is constant
Explanation: Every point on an equipotential surface has the same potential.
Reference: Standard electromagnetic theory: electric potential
Question 911
Electromagnetic TheoryElectric Flux Density

The SI unit of electric flux density D is?

  • AC/m²
  • BV/m
  • CA/m
  • DT
Report an error
Correct Answer: A. C/m²
Explanation: Electric flux density is measured in coulombs per square metre.
Reference: Standard electromagnetic theory: electric flux density
Question 912
Electromagnetic TheoryGauss's Law

Gauss’s law for the electric field in integral form states that the total electric flux of D through a closed surface equals?

  • AEnclosed free charge
  • BTotal current through the surface
  • CMagnetic flux inside the surface
  • DElectric potential on the surface
Report an error
Correct Answer: A. Enclosed free charge
Explanation: Gauss's law states that the closed-surface flux of D equals enclosed free charge.
Reference: Standard electromagnetic theory: gauss's law
Question 913
Electromagnetic TheoryMaxwell Equations Basics

The divergence form of Gauss’s law is?

  • Adiv D = rho_v
  • Bcurl D = rho_v
  • Cdiv B = rho_v
  • Dcurl E = rho_v
Report an error
Correct Answer: A. div D = rho_v
Explanation: The differential form is ∇·D=ρv.
Reference: Standard electromagnetic theory: maxwell equations basics
Question 914
Electromagnetic TheoryElectrostatics Fundamentals

In electrostatics, the curl of electric field E is?

  • AZero
  • BEqual to charge density
  • CEqual to current density
  • DAlways infinite
Report an error
Correct Answer: A. Zero
Explanation: An electrostatic electric field is conservative, hence ∇×E=0.
Reference: Standard electromagnetic theory: electrostatics fundamentals
Question 924
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
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Question 926
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 927
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 928
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 929
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 931
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 932
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 934
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 941
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 946
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
Question 948
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 949
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
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Question 951
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 955
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 956
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 960
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 963
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
Question 965
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 966
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 967
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 971
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 973
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 974
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 975
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
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Question 976
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 977
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 978
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 980
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 982
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 983
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
Question 984
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 985
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 986
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 989
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 990
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 996
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 999
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
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