# Electromagnetics & Transmission Lines Questions and Answers

**1) In accordance to Newton’s law, if two bodies m _{1} & m_{2} are separated by a distance R, then what would be the value of gravitational force between them?**

**a.** m_{1}m_{2} G/R^{2}

**b.** m_{1}m_{2}/R^{2}

**c.** m_{1}m_{2} G^{2}/R

**d.** (m_{1}m_{2})^{2} G/R

**ANSWER: (a) m _{1}m_{2} G/R^{2}**

**2) According to coulomb’s law, what do the force between two point charges proportional to?**

**a.** Addition of charges

**b.** Difference of charges

**c.** Product of charges

**d.** Integration of charges

**ANSWER: (c) Product of charges**

**3) Which type of phenomenon is likely to occur, if two charges possess opposite sign?**

**a.** Force of attraction

**b.** Force of repulsion

**c.** Force of stability

**d.** Force of equality

**ANSWER: (a) Force of attraction**

**4) If a negative charge is absent corresponding to Faraday’s experiment of concentric spheres, then where do the flux lines show termination?**

**a.** At zero

**b.** At unity

**c.** At infinity

**d.** At radial field

**ANSWER: (c) At infinity**

**5) Flux lines never _________**

1. Cross each other

2. Depend on the medium where the charges are located

3. Show radial outward direction

4. Start from positive charge

**a.** 1 & 2

**b.** 3 & 4

**c.** 1 & 4

**d.** 2 & 3

**ANSWER: (a) 1 & 2**

**6) During the representation of relationship between flux density and electric field density, what would be the value of relative permittivity for air medium?**

**a.** 0

**b.** 1

**c.** 8.85 x 10^{-12} F/m

**d.** ∞

**ANSWER: (b) 1**

**7) During the movement of a charge, potential energy undergoes _________**

**a.** Expansion

**b.** Compression

**c.** Radiation

**d.** Reflection

**ANSWER: (a) Expansion**

**8) The phenomenon of work done while moving a point charge in presence of an electric field is independent of _______**

**a.** Position

**b.** Force

**c.** Path

**d.** All of the above

**ANSWER: (c) Path**

**9) Work done becomes zero, if the selected path is located in _______ direction to electric field intensity (E)**

**a.** Parallel

**b.** Perpendicular

**c.** Opposite

**d.** Adjacent

**ANSWER: (b) Perpendicular**

**10) If the motion of charge (Q) is against the electric field with an additional requirement of external force, then what would be the nature of work done?**

**a.** Positive

**b.** Negative

**c.** Null (zero)

**d.** Infinity

**ANSWER: (a) Positive**

**11) Which law/principle of conservation provides the basis for the continuity equation of current?**

**a.** Mass action

**b.** Energy

**c.** Charge

**d.** Momentum

**ANSWER: (c) Charge**

**12) Rate of decrease in charge for volume ‘V’ bounded by a surface is equal to ______**

**a.** Incoming current rate

**b.** Outgoing current rate

**c.** Stable current rate

**d.** None of the above

**ANSWER: (b) Outgoing current rate**

**13) Which among the following elements is/are not possessed by steady state current?**

**a.** Source

**b.** Sink

**c.** Both a and b

**d.** None of the above

**ANSWER: (c) Both a and b**

**14) Which among the following equation shows the correct relationship between electric field intensity and electric flux density?**

**a.** D_{t} = ε_{0} E_{t}

**b.** E_{t} = ε_{0} D_{t}

**c.** D_{t} = E_{t}/ε_{0}

**d.** (D_{t} + E_{t}) = 1

**ANSWER: (a) D _{t} = ε_{0} E_{t}**

**15) In the equation D _{N} = ρ_{s}, the normal component of electric flux density is equal to __________ **

**a.** Surface charge density

**b.** Volume charge density

**c.** Line charge density

**d.** Surface area

**ANSWER: (a) Surface charge density**

**16) Which among the following is not a boundary condition between the conductor and the dielectric (ε = ε _{0} ε_{r})?**

**a.** E_{t} = 0

**b.** D_{t} = 1

**c.** D_{N} = ρ_{s}

**d.** EN = ρ_{s} / ε_{0}ε_{r}

**ANSWER: (b) D _{t} = 1**

**17) Consider the statements related to the case of boundary between two conductors. Which among them is/are incorrect?**

**a.** Electric field must be parallel to the surface of good conductor

**b.** Static electric field inside the conductor is always zero

**c.** Surface of conductor is always an equipotential surface

**d.** All of the above

**ANSWER: (a) Electric field must be parallel to the surface of good conductor**

**18) In a magnetic flux density, the total magnetic lines of force crossing a unit area in plane to the direction of flux are at _______**

**a.** Acute angles

**b.** Obtuse angles

**c.** Right angles

**d.** None of the above

**ANSWER: (c) Right angles**

**19) What does the constant ‘μ’ indicate, while specifying the relation between magnetic flux density (B) and magnetic field intensity (H)?**

**a.** Persistivity

**b.** Permittivity

**c.** Permissibility

**d.** Permeability

**ANSWER: (d) Permeability**

**20) In magnetism, Biot-Savart law is well-known as _____ law of current element**

**a.** Ampere’s

**b.** Coulomb’s

**c.** Joule’s

**d.** Ohm’s

**ANSWER: (a) Ampere’s**

**21) According to Biot-Savart law, which parameter/s exhibit/s an/the inverse relationship to the differential magnetic field intensity (dH)?**

**a.** Current

**b.** Magnitude of differential length

**c.** Sine of angle between filament & line connecting differential length to point

**d.** Square of the distance from differential element to point

**ANSWER: (d) Square of the distance from differential element to point**

**22) What does Maxwell’s equation derived from Faraday’s law, known as?**

**a.** Motional Induction

**b.** Stationary Induction

**c.** Transformer Induction

**d.** Transistor Induction

**ANSWER: (c) Transformer Induction**

**23) According to Lenz’s law, if a magnet is moved away from the coil, which pole should be produced in the core by the current in order to resist the movement of magnet?**

**a.** North pole

**b.** South pole

**c.** Both a and b

**d.** None of the above

**ANSWER: (b) South pole**

**24) Which conceptual notion introduced by Maxwell, indicates the generation of magnetic field in an empty free space?**

**a.** Displacement current

**b.** Velocity Vector current

**c.** Acceleration current

**d.** Projectile current

**ANSWER: (a) Displacement current**

**25) Which among the following is also regarded as Twin-lead transmission line?**

**a.** Open-wire

**b.** Underground cable

**c.** Co-axial cable

**d.** Waveguide

**ANSWER: (a) Open-wire**

**26) Which type of transmission line/s exhibit/s less capacitance in comparison to underground cables?**

**a.** Open-wire

**b.** Co-axial cables

**c.** Waveguides

**d.** All of the above

**ANSWER: (a) Open-wire**

**27) By which phenomenon does the energy transmission take place between the walls of the tube in waveguides?**

**a.** Reflection

**b.** Refraction

**c.** Dispersion

**d.** Absorption

**ANSWER: (a) Reflection**

**28) Which points have maximum magnitude along the line?**

**a.** Nodes

**b.** Antinodes

**c.** Both a and b

**d.** None of the above

**ANSWER: (b) Antinodes**

**29) What is the magnitude of current or voltage at the nodes of a line?**

**a.** Zero

**b.** Unity

**c.** Infinite

**d.** None of the above

**ANSWER: (a) Zero**

**30) What does the line showing termination at R _{0} with an absence of standing wave and node/anti-node, known as?**

**a.** Smooth line

**b.** Rough line

**c.** Load line

**d.** Point line

**ANSWER: (a) Smooth line**

**31) On which factors does the magnitude of force depend, according to Coulomb’s law?**

**a.** Size and shape of charges

**b.** Sign (polarity) of charges

**c.** Medium in which charges are placed

**d.** Displacement shown by the charges

**ANSWER: (c) Medium in which charges are placed**

**32) Which among the following statements related to point charge is/are true?**

**a.** Geometrical dimensions of point charges are negligible

**b.** Point charge is basically an electric charge located at any surface or space

**c.** Variation in the number of electrons in an atom constitutes the charge

**d.** All of the above

**ANSWER: (d) All of the above**

**33) In the vector notation of force F _{21}, what does the second number at suffix indicate?**

**a.** Force exerted by the point charge

**b.** Force exerted on a point charge

**c.** Both a and b

**d.** None of the above

**ANSWER: (b) Force exerted on a point charge**

**34) What is the purpose of Gauss’s law?**

**a.** To determine the enclosed charge

**b.** To estimate the flux passing through the closed surface

**c.** Both a and b

**d.** None of the above

**ANSWER: (c) Both a and b**

**35) The field is said to have zero divergence, if the number of field lines arriving are ______ to/than the number of field lines departing the volume**

**a.** Less

**b.** Greater

**c.** Equal

**d.** None of the above

**ANSWER: (c) Equal**

**36) According to Maxwell’s first equation, the electric flux departing per unit volume is equal to _______**

**a.** Line charge density

**b.** Surface charge density

**c.** Volume charge density

**d.** None of the above

**ANSWER: (c) Volume charge density**

**37) Under which condition/s of the selected path, is the work done said to be zero?**

**a.** Open loop

**b.** Closed loop

**c.** Both a and b

**d.** None of the above

**ANSWER: (b) Closed loop**

**38) Along the parabola x = 2y ^{2}, what will be the value of work done in carrying the charge of -4μJ, from point P_{1} (3,1,-1) to P_{2} (4,2,-1) in the electric field E = y a_{x} + x a_{y} ?**

**a.** 4 μJ

**b.** 14 μJ

**c.** 28 μJ

**d.** 56 μJ

**ANSWER: (d) 56 μJ**

**39) Electric field intensity is defined as the ratio of _____ to the test charge.**

**a.** Displacement

**b.** Pressure

**c.** Force

**d.** Current

**ANSWER: (c) Force**

**40) Which parameter is considered as a reference for the measurement of zero potential? **

**a.** Field

**b.** Ground

**c.** V_{CC}

**d.** None of the above

**ANSWER: (b) Ground**

**41) What is the value of rate of change of charge density for steady state current?**

**a.** 0

**b.** 0.5

**c.** 1

**d.** ∞

**ANSWER: (a) 0**

**42) Which consequence/s is/are likely to occur due to polarization?**

**a.** Increase in electric flux density

**b.** Decrease in electric flux density

**c.** Stability in electric flux density

**d.** None of the above

**ANSWER: (a) Increase in electric flux density**

**43) If the material is isotropic and linear, what would be the direction of electric field intensity and the polarization at each point?**

**a.** Parallel

**b.** Perpendicular

**c.** Both a and b

**d.** None of the above

**ANSWER: (a) Parallel**

**44) Poisson’s equation is derived from ________**

**a.** Laplace equation

**b.** Guass law

**c.** Thevenin’s theorem

**d.** Kirchoff’s law

**ANSWER: (b) Guass law**

**45) If the volume charge density is found to be zero, then what would be the transformed type of Poisson’s equation especially due to presence of line, point or surface charge?**

**a.** ▾^{2} V = – (ρ_{v} / ε)

**b.** ▾^{2} V = – ρ_{v}

**c.** ▾^{2} V = 1

**d.** ▾^{2} V = 0

**ANSWER: (d) ▾ ^{2} V = 0**

**46) Consider the equation of spherical capacitor given below. What does the potential between the spheres specify?**

Equation: V = -(V_{0} / r) [ab / a-b] + V_{0}[a / a-b]

**a.** As an integral of capacitance

**b.** As a derivative of radius

**c.** As an index of radial direction

**d.** As a function of position

**ANSWER: (d) As a function of position**

**47) What is the value of cross product for two similar unit vectors?**

**a.** Zero

**b.** Infinity

**c.** Third unit vector

**d.** Negative vector

**ANSWER: (a) Zero**

**48) Which co-ordinate/s serve/s to be a function of magnitude of magnetic field intensity due to infinite long straight filament?**

**a.** 0

**b.** Φ

**c.** z

**d.** r

**ANSWER: (d) r**

**49) What is the direction of magnetic field intensity vector due to infinite long straight filament?**

**a.** Radial

**b.** Elliptical

**c.** Parabolic

**d.** Circumferential

**ANSWER: (d) Circumferential**

**50) In Ampere’s circuital law, what is the purpose of an ‘Amperian Path’?**

**a.** Computation of magnetic field intensity

**b.** Determination of differential element of path length

**c.** Estimation of electric flux density

**d.** Detection of loop in a constant plane

**ANSWER: (a) Computation of magnetic field intensity**

**51) Which nature of applied voltage results in the flow of conduction current in the displacement current concept?**

**a.** Constant

**b.** Variable

**c.** Both a and b

**d.** None of the above

**ANSWER: (b) Variable**

**52) Which form of Maxwell’s equation specifies the fundamental relationship between the electric and magnetic fields in time varying field?**

**a.** Point form

**b.** Integral form

**c.** Exponential form

**d.** None of the above

**ANSWER: (a) Point form**

**53) Maxwell’s second equation of static field is a point form of _________**

**a.** Ampere’s circuital law

**b.** Guass’s law

**c.** Lenz law

**d.** Biot Savart law

**ANSWER: (a) Ampere’s circuital law**

**54) If the rate of attenuation is high for good conductors at radio frequency, where does an input wave get reduced to?**

**a.** Zero

**b.** Infinity

**c.** Minor proportion of its initial strength value

**d.** Major proportion of its final strength value

**ANSWER: (c) Minor proportion of its initial strength value**

**55) Which primary constant of transmission line is exhibits its dependency of value on the cross-sectional area of conductors?**

**a.** Resistance (R)

**b.** Inductance (I)

**c.** Conductance (G)

**d.** Capacitance (C)

**ANSWER: (a) Resistance (R)**

**56) Which parameter is much larger than the resistance at radio frequencies in RF circuits?**

**a.** Inductive reactance

**b.** Capacitive susceptance

**c.** Shunt conductance

**d.** Series admittance

**ANSWER: (a) Inductive reactance**

**57) Which operation is performed over the in phase incident and reflected waves in order to obtain maximum voltage of SWR?**

**a.** Addition

**b.** Subtraction

**c.** Differentiation

**d.** Integration

**ANSWER: (a) Addition**

**58) What would be the Standing Wave Ratio (SWR) for a line with reflection coefficient equal to 0.49?**

**a.** 0.01

**b.** 2.12

**c.** 2.921

**d.** 3.545

**ANSWER: (c) 2.921**

**59) How does the short-circuited line behave for the first λ/4 distance if input impedance is purely reactive?**

**a.** As an inductance

**b.** As a resistance

**c.** As a capacitance

**d.** As a conductance

**ANSWER: (a) As an inductance**

**60) An electric field exhibits variation corresponding to _________**

**a.** Position

**b.** Time

**c.** Both a and b

**d.** None of the above

**ANSWER: (c) Both a and b**

**61) At which point it becomes necessary to determine the electric field intensity?**

**a.** Field Point

**b.** Source Point

**c.** Sink Point

**d.** Static Point

**ANSWER: (a) Field Point**

**62) What kind of function is an electric field intensity with respect to the value of charge?**

**a.** Linear

**b.** Angular

**c.** Delta

**d.** Sinc

**ANSWER: (a) Linear**

**63) Under which category of charge distribution does the cathode ray tube belong to? **

**a.** Point Charge

**b.** Line Charge

**c.** Surface Charge

**d.** Volume Charge

**ANSWER: (d) Volume Charge**

**64) Which form of Gauss’s law is regarded as Maxwell’s first equation?**

**a.** Point form

**b.** Line form

**c.** Angular form

**d.** Exponential form

**ANSWER: (a) Point form**

**65) Consider the equation given below. What does it represent from the following?**

Equation: ▾.D = (∂D_{x} / ∂x) + (∂D_{y} / ∂y) + (∂D_{z} / ∂z)

**a.** Divergence in Cartesian system

**b.** Divergence in Cylindrical system

**c.** Divergence in Spherical system

**d.** None of the above

**ANSWER: (a) Divergence in Cartesian system**

**66) Basically, the flux lines which are represented by the lines of force are regarded as _________**

**a.** Branch lines

**b.** Node lines

**c.** Stream lines

**d.** Loop lines

**ANSWER: (c) Stream lines**

**67) Which among the following represents a scalar quantity?**

**a.** Velocity

**b.** Momentum

**c.** Force

**d.** Potential

**ANSWER: (d) Potential**

**68) If a point ‘P’ has spherical coordinates (r = 5000, θ = 0°, ∅ = 0°), then what will be its equivalent value (x,y,z) in Cartesian co-ordinate system?**

**a.** (5000, 0, 0)

**b.** (0, 5000, 0)

**c.** (0, 0, 5000)

**d.** (0, 0, 0)

**ANSWER: (c) (0, 0, 5000)**

**69) Consider a point charge of about 10nC is located at origin. If V = 4V at (0,5,7) and point A (-6,4,12), then what would be the value of potential at point B (2,10,14)?**

**a.** 1.261 V

**b.** -1.261 V

**c.** 2.696 V

**d.** -2.696 V

**ANSWER: (b) -1.261 V**

**70) According to the definition of dielectric strength of dielectric medium, which value of electric field give rise to an occurrence of dielectric breakdown phenomenon?**

**a.** Maximum

**b.** Minimum

**c.** Initial

**d.** Final

**ANSWER: (b) Minimum**

**71) If the magnitude of E for a dielectric material is 0.12 mV/m along with electric susceptibility of about 4, what would be the magnitude of polarization?**

**a.** 2.20 x 10^{-15} c/m^{2}

**b.** 3.89 x 10^{-15} c/m^{2}

**c.** 4.24 x 10^{-15} c/m^{2}

**d.** 5.64 x 10^{-15} c/m^{2}

**ANSWER: (c) 4.24 x 10 ^{-15} c/m^{2}**

**72) For an estimated value of polarization (P) = 4 .42 x 10 ^{-10} c/m^{2} and the availability of 4 x 10^{18}dipoles/m^{3}, what will be the value of average dipole moment for dielectric material?**

**a.** 0.05 x 10^{-28}

**b.** 1.105 x 10^{-28}

**c.** 1.205 x 10^{-28}

**d.** 1.405 x 10^{-28}

**ANSWER: (b) 1.105 x 10 ^{-28}**

**73) Which type of capacitor possesses magnitude of flux density equivalent to its surface charge density?**

**a.** Parallel Plate capacitor

**b.** Spherical Capacitor

**c.** Co-axial cable capacitor

**d.** None of the above

**ANSWER: (a) Parallel Plate capacitor**

**74) If the medium is different than air, then what would be the equation of capacitance for a co-axial cable capacitor?**

**a.** C = ε_{0} ε_{r} A / d

**b.** C = 4π ε_{0} ε_{r} [ab / a – b]

**c.** C = 2π ε_{0} ε_{r} L / ln (b/a)

**d.** C = 2π ε_{0} ε_{r} R

**ANSWER: (c) C = 2π ε _{0} ε_{r} L / ln (b/a)**

**75) According to Maxwell’s first equation in a point form for the static field, the electric flux per unit volume by leaving a small value is equal to __________**

**a.** Zero

**b.** Current density

**c.** Volume charge density

**d.** Magnetic field intensity

**ANSWER: (c) Volume charge density**

**76) How is the relation between energy transfer and the electric and magnetic fields specified?**

**a.** By Poynting theorem

**b.** By Stoke’s theorem

**c.** By Helmholtz theorem

**d.** By Lagrange’s theorem

**ANSWER: (a) By Poynting theorem**

**77) The ratio of magnitudes of electric field intensity to the magnetic field intensity is regarded as ________**

**a.** Intrinsic Impedance

**b.** Characteristic Impedance

**c.** Both a and b

**d.** None of the above

**ANSWER: (c) Both a and b**

**78) What would be the depth of penetration for copper at 2 MHz frequency with σ = 5.8 x 10 ^{7}?**

**a.** 46.72 μm

**b.** 56.90 μm

**c.** 66.08 μm

**d.** 76.34 μm

**ANSWER: (a) 46.72 μm**

**79) For a transmission line with propagation constant γ = 0.650 + j 2.55, what will be the value of phase velocity for 1 kHz frequency?**

**a.** 1.18 x 10^{3} km/sec

**b.** 1.50 x 10^{3} km/sec

**c.** 2.46 x 10^{3} km/sec

**d.** 4.58 x 10^{3} km/sec

**ANSWER: (c) 2.46 x 10 ^{3} km/sec**

**80) Which lossless element is inserted between source and load in addition to an ideal transformer in order to reduce the effect of reflection loss phenomenon by image matching?**

**a.** Amplitude shifter

**b.** Phase shifter

**c.** Frequency divider

**d.** Voltage divider

**ANSWER: (b) Phase shifter**

**81) What is the phase variation range for reflection coefficient in the transmission lines?**

**a.** 0° to 90°

**b.** 90° to 150°

**c.** 0° to 180°

**d.** 90° to 360°

**ANSWER: (c) 0° to 180°**

**82) After what wavelength does the nature of graph get reversed for the input impedance of open-circuited line?**

**a.** λ/2

**b.** λ/4

**c.** λ/8

**d.** λ/16

**ANSWER: (b) λ/4**

**83) If the quarter line is short-circuited, then it acts as _______**

**a.** Conductor

**b.** Insulator

**c.** Semiconductor

**d.** Power regulator

**ANSWER: (b) Insulator**

**84) According to Smith diagram, where should be the position of reflection coefficient value for a unity circle with unity radius?**

**a.** On or inside the circle

**b.** Outside the circle

**c.** Both a and b

**d.** None of the above

**ANSWER: (a) On or inside the circle**

**85) The constant x-circles of Smith chart becomes smaller due to increase in the value of ‘x’ from ______**

**a.** 0 to π

**b.** 0 to 2π

**c.** 0 to π /2

**d.** 0 to ∞

**ANSWER: (d) 0 to ∞**