# Electromagnetics & Transmission Lines Questions and Answers

1)   In accordance to Newton’s law, if two bodies m1 & m2 are separated by a distance R, then what would be the value of gravitational force between them?

a. m1m2 G/R2
b. m1m2/R2
c. m1m2 G2/R
d. (m1m2)2 G/R

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

b. Difference of charges
c. Product of charges
d. Integration 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

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

5)   Flux lines never _________

1. Cross each other
2. Depend on the medium where the charges are located
4. Start from positive charge

a. 1 & 2
b. 3 & 4
c. 1 & 4
d. 2 & 3

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. ∞

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

a. Expansion
b. Compression
d. Reflection

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

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

a. Parallel
b. Perpendicular
c. Opposite

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

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

a. Mass action
b. Energy
c. Charge
d. Momentum

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

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. Dt = ε0 Et
b. Et = ε0 Dt
c. Dt = Et0
d. (Dt + Et) = 1

ANSWER: (a) Dt = ε0 Et

15)   In the equation DN = ρs, 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

16)   Which among the following is not a boundary condition between the conductor and the dielectric (ε = ε0 εr)?

a. Et = 0
b. Dt = 1
c. DN = ρs
d. EN = ρs / ε0εr

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

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

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

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

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

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

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

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

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

28)   Which points have maximum magnitude along the line?

a. Nodes
b. Antinodes
c. Both a and b
d. None of the above

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

30)   What does the line showing termination at R0 with an absence of standing wave and node/anti-node, known as?

a. Smooth line
b. Rough line
d. Point 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 F21, 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

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

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

38)   Along the parabola x = 2y2, what will be the value of work done in carrying the charge of -4μJ, from point P1 (3,1,-1) to P2 (4,2,-1) in the electric field E = y ax + x ay ?

a. 4 μJ
b. 14 μJ
c. 28 μJ
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

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

a. Field
b. Ground
c. VCC
d. None of the above

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

a. 0
b. 0.5
c. 1
d. ∞

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

44)   Poisson’s equation is derived from ________

a. Laplace equation
b. Guass law
c. Thevenin’s theorem
d. Kirchoff’s 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 = – (ρv / ε)
b. ▾2 V = – ρv
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 = -(V0 / r) [ab / a-b] + V0[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

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

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

b. Elliptical
c. Parabolic
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

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

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

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)

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

a. Inductive reactance
b. Capacitive susceptance
c. Shunt conductance

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

b. Subtraction
c. Differentiation
d. Integration

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

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

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

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

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

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

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

Equation: ▾.D = (∂Dx / ∂x) + (∂Dy / ∂y) + (∂Dz / ∂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

67)   Which among the following represents a scalar quantity?

a. Velocity
b. Momentum
c. Force
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)

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

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

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/m2
b. 3.89 x 10-15 c/m2
c. 4.24 x 10-15 c/m2
d. 5.64 x 10-15 c/m2

ANSWER:  (c) 4.24 x 10-15 c/m2

72)   For an estimated value of polarization (P) = 4 .42 x 10-10 c/m2 and the availability of 4 x 1018dipoles/m3, 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

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

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

a. C = ε0 εr A / d
b. C = 4π ε0 εr [ab / a – b]
c. C = 2π ε0 εr L / ln (b/a)
d. C = 2π ε0 εr R

ANSWER: (c) C = 2π ε0 εr 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

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

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 107?

a. 46.72 μm
b. 56.90 μm
c. 66.08 μm
d. 76.34 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 103 km/sec
b. 1.50 x 103 km/sec
c. 2.46 x 103 km/sec
d. 4.58 x 103 km/sec
ANSWER: (c) 2.46 x 103 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

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°

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

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

a. Conductor
b. Insulator
c. Semiconductor
d. Power regulator

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 ∞