ECE : Electromagnetic Field Theory MCQs with Answers

1 .
The right hand rule for determining the direction of the induced EMF was introduced by
A)  Lenz
B)  Fleming
C)   Maxwell
D)  Faraday

Correct Answer :   Fleming

Explanation : The right hand rule for determining the direction of induced EMF was introduced by Fleming and it is well known as Fleming’s right hand rule. It is used to find the direction of induced emf of a generator.

2 .
A loop antenna is a commonly used for
A)  Radar
B)  Satellite communication
C)  Direction finding
D)  All of the above

Correct Answer :   Direction finding

3 .
ZL = 200 Ω and it is desired that Zi = 50 Ω The quarter wave transformer should have a characteristic impedance of
A)  40 Ω
A)  
B)  100 Ω
B)  
C)  10000 Ω
C)  
D)  100000 Ω
D)  

Correct Answer :   100 Ω

4 .
A broadside array consisting of 200 cm wavelength with 10 half-wave dipole spacing 10 cm. And if each array element feeding with 1 amp. current and operating at same frequency then find the half power beamwidth
A)  2°
A)  
B)  4°
B)  
C)  10°
C)  
D)  16°
D)  

Correct Answer :   2°

Explaination :

5 .
Refractive index of glass is 1.5. Find the wavelength of a beam of light with a frequency of 1014 Hz in glass. Assume velocity of light is 3 x 108 m/sec in vacuum.
A)  4 μm
A)  
B)  3 μm
B)  
C)  2 μm
C)  
D)  1 μm
D)  

Correct Answer :   2 μm

Explaination :

6 .
A broadside array operating at 100 cm wavelength consist of 4 half-wave dipoles spaced 50 cm apart. Each element carries radio frequency current in the same phase and of magnitude 0.5 A. The radiated power will be
A)  18.25 W
A)  
B)  36.5 W
B)  
C)  73 W
C)  
D)  196 W
D)  

Correct Answer :   196 W

Explaination :

7 .
A wave is propagated in a waveguide at frequency of 9 GHz and separation is 2 cm between walls find cut off wavelength for dominant mode.
A)  1 cm
B)  2 cm
C)  4 cm
D)  8 cm

Correct Answer :   4 cm

Explanation :

8 .
Find the radiation resistance of an antenna of length λ/10 meter?
A)  7.8 Ω
B)  8 Ω
C)  78 Ω
D)  780 Ω

Correct Answer :   7.8 Ω

Explanation :

9 .
Two parallel plates are separated by a distance D charged by V volt. The field intensity E is given by,
A)   V × D
B)   V / D
C)   V × D²
D)   V² / D

Correct Answer :   V / D

Explanation : Electric field intensity between two points is always expressed as the potential difference between these two points divided by the distance between them. The strength of electric field or electric field intensity is measured by volt per meter or newton per meter.

10 .
Whenever the magnetic flux changes with respect to an electric conductor or a coil, an EMF is induced in the conductor is Faraday's
A)  first law
B)  second law
C)  third law
D)  fourth law

Correct Answer :   first law

Explanation : Faraday’s law of electromagnetic induction states

1. Whenever a changing flux links with a conductor, there will be an EMF induced in the conductor.
2. The magnitude of this induced EMF is directly proportional to the rate of change of flux linkage with respect to time.

These two statements are well-known as Faraday’s first and second law of electromagnetic induction respectively.

11 .
The divergence of a vector is a scalar, while the curl of a vector is another
A)  Vector
B)  Scalar
C)  Unit vector
D)  None of the above

Correct Answer :   Vector

12 .
Which antenna is a wideband antenna?
A)  Hertz antenna
B)  Marconi antenna
C)  Folded dipole
D)  None of the above

Correct Answer :   Folded dipole

13 .
The potential that appears at a point in space due to the current which caused it is called potential
A)  Oscillating
B)  Retardation
C)  Accelerating
D)  Lagging the current

Correct Answer :   Retardation

14 .
The minimum height of outer atmosphere is
A)  100 km
B)  150 km
C)  200 km
D)  400 km

Correct Answer :   400 km

15 .
The radiation pattern of a parabola antenna is
A)  Highly directional
B)  Omnidirectional
C)  A figure of directional
D)  None of the above

Correct Answer :   Highly directional

16 .
The virtual height of an ionospheric layer is __________ true height
A)  Equal to
B)  Less than
C)  Higher than
D)  None of the above

Correct Answer :   Higher than

17 .
When two vectors are perpendicular, their
A)  Cross product is zero
B)  Dot product is zero
C)  Both are zero
D)  Both are not necessarily zero

Correct Answer :   Dot product is zero

Explanation : Dot product of two perpendicular vectors is given by A.B = |a||b|cos 90, which is zero. Thus, dot product is zero and vectors are perpendicular.

18 .
The cross product of the vectors 3i + 4j – 5k and –i + j – 2k is,
A)  3i – 11j + 7k
B)  -3i – 11j – 7k
C)  -3i + 11j – 7k
D)  -3i + 11j + 7k

Correct Answer :   -3i + 11j + 7k

Explanation : Cross product of two vectors is, A X B = (a2*b3 – b2*a3)i – (a1*b3 – b1*a3)j + (a1*b2 – b1*a2)k. Using the formula, the answer can be calculated.

19 .
The work done of vectors force F and distance d, separated by angle θ can be calculated using,
A)  Dot product
B)  Cross product
C)  Addition of two vectors
D)  Cannot be calculated

Correct Answer :   Dot product

Explanation : Force is a vector quantity, whereas distance is scalar. Work is defined as the product of force and distance, which is given by dot product.

20 .
Find whether the vectors are parallel, (-2,1,-1) and (0,3,1)
A)  Parallel
B)  Not parallel
C)  Data insufficient
D)  Collinearly parallel

Correct Answer :   Not parallel

Explanation : Two vectors are parallel when their cross product is zero. Since their cross product is 4i + 2j – 6k (non-zero), the vectors are not parallel.

21 .
Lorentz force is based on,
A)  Dot product
B)  Cross product
C)  Both dot and cross product
D)  Independent of both

Correct Answer :   Cross product

Explanation : Lorentz force is given by, F = q (v x B).Thus cross product is the answer.

22 .
Which of the following is not true?
A)  A . (B . C) = scalar value
B)  A . (B x C) = scalar value
C)  A x (B . C) = scalar value
D)  A x (B x C) = vector value

Correct Answer :   A x (B . C) = scalar value

Explanation : Cross product of dot product of two vectors is a vector value.

23 .
The Cartesian system is also called as
A)  Space coordinate system
B)  Circular coordinate system
C)  Spherical coordinate system
D)  Rectangular coordinate system

Correct Answer :   Rectangular coordinate system

Explanation : The other name for Cartesian is rectangular system, which is given by (x,y,z).

24 .
The volume of a parallelepiped in Cartesian is
A)  dV = dx dy
B)  dV = dy dz
C)  dV = dx dz
D)  dV = dx dy dz

Correct Answer :   dV = dx dy dz

Explanation : The volume of a parallelepiped is given by product of differential length, breadth and height.

25 .
A charge is placed in a square container. The position of the charge with respect to the origin can be found by
A)  Circular system
B)  Cartesian system
C)  Spherical system
D)  Space coordinate system

Correct Answer :   Cartesian system

Explanation : Since the container possesses dimensions of a square (length, breadth and height), it can be found by Cartesian system.

26 .
The angular separation between the vectors A = 4i + 3j + 5k and B = i – 2j + 2k is (in degrees)
A)  65.8
B)  66.8
C)  67.8
D)  68.8

Correct Answer :   67.8

Explanation : The dot product the vector is 8. Angle of separation is cos θ = 8/ (7.07 X 3) = 0.377 and θ = cos-1(0.377) = 67.8.

27 .
Transform the vector A = 3i – 2j – 4k at P(2,3,3) to cylindrical coordinates
A)  -3.6j – 4k
B)  -3.6j + 4k
C)  3.6j – 4k
D)  3.6j + 4k

Correct Answer :   -3.6j – 4k

Explanation : Convert the Cartesian form to cylindrical form by formula and substitute the points to get -3.6j – 4k.

28 .
Vector transformation followed by coordinate point substitution and vice-versa, both given the same result. Choose the best answer.
A)  Possible in all cases
B)  Possible, when the vector is variable
C)  Possible, when the vector is constant
D)  None of the above

Correct Answer :   Possible, when the vector is constant

Explanation : The order of vector transformation and point substitution will not affect the result, only when the vector is a constant.

29 .
The distance vector is obtained in
A)  Circular coordinate system
B)  Spherical coordinate system
C)  Cartesian coordinate system
D)  Space coordinate system

Correct Answer :   Space coordinate system

Explanation : Vector formed by connecting two points in space is distance vector. Thus, it is obtained in space coordinate system.

30 .
The divergence of distance vector is
A)  0
B)  1
C)  2
D)  3

Correct Answer :   3

Explanation : The distance vector of any coordinates is generally, r = xi + yj + zk. The divergence of r is 1 + 1 + 1 = 3.

31 .
The unit vector to the points p1(0,1,0), p2(1,0,1), p3(0,0,1) is
A)  (-i – j)/1.414
B)  (-i – k)/1.414
C)  (-j – k)/1.414
D)  (-i – j – k)/1.414

Correct Answer :   (-j – k)/1.414

Explanation : The cross product of p1, p2, p3 is a X b = -j – k and its magnitude is 1.414. The unit normal vector is given by, (-j –
k)/1.414.

32 .
The polar form of Cartesian coordinates is
A)  Space coordinates
B)  Circular coordinates
C)  Cartesian coordinates
D)  Spherical coordinates

Correct Answer :   Circular coordinates

Explanation : The radius in the polar coordinates is the Pythagorean triplet-(r,x,y).Thus it is the circular coordinates.

33 .
The work-electric field relation is given by
A)  Line integral
B)  Surface integral
C)  Volume integral
D)  Relation impossible

Correct Answer :   Line integral

Explanation : The work done is given by, W = -Q ∫E dl. Thus it is line integral.

34 .
Find the projection of A on B. Given A = 10j + 3k and B = 4j + 5k.
A)  6
B)  6.25
C)  6.5
D)  6.75

Correct Answer :   6.25

Explanation : Projection of A on B = (A . B)/|B|. Thus the answer is 40/6.4= 6.25.

35 .
The cylindrical coordinate system is also referred to as
A)  Space system
B)  Cartesian system
C)  Spherical system
D)  Circular system

Correct Answer :   Circular system

Explanation : The cylindrical coordinates(r,φ,z) is also called as circular system and is used for systems with circular dimensions.

36 .
Transform the vector B=yi+(x+z)j located at point (-2,6,3) into cylindrical coordinates.
A)  (6.325,73.57,3)
B)  (6.325,71.57,3)
C)  (6.325,-71.57,3)
D)  (6.325,-73.57,3)

Correct Answer :   (6.325,-71.57,3)

Explanation : ρ = √(x2+y2) = √40 = 6.325
Φ = tan-1(y/x) = tan-1(-6/2) = -71.57
z = 3.

37 .
A charge located at point p (5,30⁰,2) is said to be in which coordinate system?
A)  Cylindrical system
B)  Space system
C)  Spherical system
D)  Cartesian system

Correct Answer :   Cylindrical system

Explanation : The cylindrical system is of the form (ρ, φ, z), which relates the point given in the question.

38 .
Transform the spherical system B = (10/r)i + (10cos θ)j + k into cylindrical form at (5, π/2, -2)
A)  2.467i – j + 1.167k
B)  2.467i + j + 1.167k
C)  2.467i – j – 1.167k
D)  2.467i + j – 1.167k

Correct Answer :   2.467i + j + 1.167k

Explanation : The equivalent cylindrical form is given by,
B = (10sin θ/r + rcos2θ)i + j + (10cos θ/r –r sin θ cos θ)k
At (5, π/2, -2), r = √(52+-22) = √29
sin θ = 5/√29 and cos θ = -2/√29
Thus, B = 2.467i + j + 1.167k.

39 .
Rectangular waveguides dominate the circular waveguides. Find the reason.
A)  Easy to design
B)  Low cut-off frequency
C)  More wave propagation
D)  The statement is false

Correct Answer :   Easy to design

Explanation : Due to linear design, the desired dimensions can be easily constructed using rectangular waveguides than circular ones.

40 .
The pressure inside a piston cylinder is a variable of
A)  Radius
B)  Plane angle
C)  Z plane distance
D)  Constant, not a variable

Correct Answer :   Z plane distance

Explanation : Pressure varies up and down in a cylinder due to suction. Thus it is dependent on the z plane distance of the cylinder.

41 .
The mathematical perception of the gradient is said to be
A)  Slope
B)  Arc
C)  Chord
D)  Tangent

Correct Answer :   Slope

Explanation : The gradient is the rate of change of space of flux in electromagnetics. This is analogous to the slope in mathematics.

42 .
Divergence of gradient of a vector function is equivalent to
A)  Null vector
B)  Curl operation
C)  Laplacian operation
D)  Double gradient operation

Correct Answer :   Laplacian operation

Explanation : Div (Grad V) = (Del)2V, which is the Laplacian operation. A function is said to be harmonic in nature, when its Laplacian tends to zero.

43 .
Curl of gradient of a vector is
A)  Zero
B)  Unity
C)  Null vector
D)  Depends on the constants of the vector

Correct Answer :   Null vector

Explanation : Gradient of any function leads to a vector. Similarly curl of that vector gives another vector, which is always zero for all constants of the vector. A zero value in vector is always termed as null vector(not simply a zero).

44 .
The gradient can be replaced by which of the following?
A)  Surface integral
B)  Volume integral
C)  Maxwell equation
D)  Differential equation

Correct Answer :   Differential equation

Explanation : Since gradient is the maximum space rate of change of flux, it can be replaced by differential equations.

45 .
Find the gradient of the function sin x + cos y.
A)  cos x i + sin y j
B)  cos x i – sin y j
C)  sin x i – cos y j
D)  sin x i + cos y j

Correct Answer :   cos x i – sin y j

Explanation : Grad (sin x + cos y) gives partial differentiation of sin x+ cos y with respect to x and partial differentiation of sin x + cos y with respect to y and similarly with respect to z. This gives cos x i – sin y j + 0 k = cos x i – sin y j.

46 .
Compute the divergence of the vector xi + yj + zk.
A)  0
B)  1
C)  2
D)  3

Correct Answer :   3

Explanation : The vector given is a position vector. The divergence of any position vector is always 3.

47 .
Find the divergence of the vector yi + zj + xk.
A)  -1
B)  0
C)  1
D)  2

Correct Answer :   0

Explanation : Div (yi + zj + xk) = Dx(y) + Dy(z) + Dz(x), which is zero. Here D refers to partial differentiation.

48 .
Determine the divergence of F = 30 i + 2xy j + 5xz2 k at (1,1,-0.2) and state the nature of the field
A)  1, solenoidal
A)  
B)  0, solenoidal
B)  
C)  1, divergent
C)  
D)  0, divergent
D)  

Correct Answer :   0, solenoidal

Explaination : Div(F) = Dx(30) + Dy(2xy) + Dz(5xz2) = 0 + 2x + 10xz = 2x + 10xz
Divergence at (1,1,-0.2) will give zero. As the divergence is zero, field is solenoidal.
Alternate/Shortcut: Without calculation, we can easily choose option “0, solenoidal”, as by theory when the divergence is zero, the vector is solenoidal. “0, solenoidal” is the only one which is satisfying this condition.

49 .
Identify the nature of the field, if the divergence is zero and curl is also zero.
A)  Divergent, rotational
B)  Divergent, rotational
C)  Solenoidal, irrotational
D)  Solenoidal, irrotational

Correct Answer :   Solenoidal, irrotational

Explanation : Since the vector field does not diverge (moves in a straight path), the divergence is zero. Also, the path does not possess any curls, so the field is irrotational.

50 .
Which of the following theorem use the curl operation?
A)  Stoke’s theorem
B)  Green’s theorem
C)  Maxwell equation
D)  Gauss Divergence theorem

Correct Answer :   Stoke’s theorem

Explanation : The Stoke’s theorem is given by ∫ A.dl = ∫Curl(A).ds, which uses the curl operation. There can be confusion with Maxwell equation also, but it uses curl in electromagnetics specifically, whereas the Stoke’s theorem uses it in a generalised manner. Thus the best option is Stoke’s theorem.

51 .
Curl cannot be employed in which one of the following?
A)  Magic Tee
B)  Waveguides
C)  Directional coupler
D)  Isolator and Terminator

Correct Answer :   Waveguides

Explanation : In the Directional coupler, Magic Tee, Isolator and Terminator the EM waves travel both in linear and angular motion, which involves curl too. But in waveguides, as the name suggests, only guided propagation occurs (no bending or curl of waves).

52 .
Which of the following Maxwell equations use curl operation?
A)  Maxwell 1st and 2nd equation
B)  Maxwell 3rd and 4th equation
C)  All the four equations
D)  None of the above

Correct Answer :   Maxwell 1st and 2nd equation

Explanation : Maxwell 1st equation, Curl (H) = J (Ampere law)
Maxwell 2nd equation, Curl (E) = -D(B)/Dt (Faraday’s law)
Maxwell 3rd equation, Div (D) = Q (Gauss law for electric field)
Maxwell 4th equation, Div (B) = 0(Gauss law for magnetic field)
It is clear that only 1st and 2nd equations use the curl operation.

53 .
Surface integral is used to compute
A)  Area
B)  Surface
C)  density
D)  Volume

Correct Answer :   Area

Explanation : Surface integral is used to compute area, which is the product of two quantities length and breadth. Thus it is two dimensional integral.

54 .
The ultimate result of the divergence theorem evaluates which one of the following?
A)  Potential
B)  Field density
C)  Field intensity
D)  Charge and flux

Correct Answer :   Charge and flux

Explanation : Gauss law states that the electric flux passing through any closed surface is equal to the total charge enclosed by the surface. Thus, it is given by, ψ = ∫∫ D.ds= Q, where the divergence theorem computes the charge and flux, which are both the same.

55 .
If D = 2xy i + 3yz j + 4xz k, how much flux passes through x = 3 plane for which -1<y<2 and 0<z<4?
A)  12
A)  
B)  24
B)  
C)  36
C)  
D)  48
D)  

Correct Answer :   36

Explaination : By Gauss law, ψ = ∫∫ D.ds, where ds = dydz i at the x-plane. Put x = 3 and integrate at -1<y<2 and 0<z<4, we get 12 X 3 = 36.

56 .
The divergence theorem converts
A)  Surface to line integral
B)  Volume to line integral
C)  Line to surface integral
D)  Surface to volume integral

Correct Answer :   Surface to volume integral

Explanation : The divergence theorem is given by, ∫∫ D.ds = ∫∫∫ Div (D) dv. It is clear that it converts surface (double) integral to volume(triple) integral.

57 .
Using volume integral, which quantity can be calculated?
A)  area of cube
B)  volume of cube
C)  area of cuboid
D)  distance of vector

Correct Answer :   volume of cube

Explanation : The volume integral gives the volume of a vector in a region. Thus volume of a cube can be computed.

58 .
Find the value of Stoke’s theorem for y i + z j + x k.
A)  i + j
B)  j + k
C)  –i – j – k
D)  i + j + k

Correct Answer :   –i – j – k

Explanation :  The curl of y i + z j + x k is i(0-1) – j(1-0) + k(0-1) =
-i –j –k. Since the curl is zero, the value of Stoke’s theorem is zero. The function is said to be irrotational.

59 .
The Stoke's theorem uses which of the following operation?
A)  Curl
B)  Gradient
C)  Laplacian
D)  Divergence

Correct Answer :   Curl

Explanation : ∫A.dl = ∫∫ Curl (A).ds is the expression for Stoke’s theorem. It is clear that the theorem uses curl operation.

60 .
Which of the following theorem convert line integral to surface integral?
A)  Stoke’s theorem only
B)  Green’ s theorem only
C)  Stoke’s and Green’s theorem
D)  Gauss divergence and Stoke’s theorem

Correct Answer :   Stoke’s and Green’s theorem

Explanation : The Stoke’s theorem is given by ∫A.dl = ∫∫ Curl (A).ds. Green’s theorem is given by, ∫ F dx + G dy = ∫∫ (dG/dx – dF/dy) dx dy. It is clear that both the theorems convert line to surface integral.

61 .
Find the value of Stoke’s theorem for A = x i + y j + z k. The state of the function will be
A)  Divergent
B)  Solenoidal
C)  Rotational
D)  Curl free

Correct Answer :   Curl free

Explanation : Since curl is required, we need not bother about divergence property. The curl of the function will be i(0-0) – j(0-0) + k(0-0) = 0. The curl is zero, thus the function is said to be irrotational or curl free.

62 .
The Stoke's theorem can be used to find which of the following?
A)  Area enclosed by a function in the given region
B)  Linear distance
C)  Curl of the function
D)  Volume enclosed by a function in the given region

Correct Answer :   Area enclosed by a function in the given region

Explanation : It states that the line integral of a function gives the surface area of the function enclosed by the given region. This is computed using the double integral of the curl of the function.

63 .
The conductivity of a material with current density 1 unit and electric field 200 μV is
A)  2000
B)  3000
C)  4000
D)  5000

Correct Answer :   5000

Explanation : The current density is given by, J = σE. To find conductivity, σ = J/E = 1/200 X 10-6 = 5000.

64 .
The resistivity of a material with resistance 200 ohm, length 10m and area twice that of the length is
A)  200
B)  300
C)  400
D)  500

Correct Answer :   400

Explanation : Resistance calculated from Ohm’s law and Stoke’s theorem will be R = ρL/A. To get resistivity, ρ = RA/L = 200 X 20/10 = 400.

65 .
Mathematically, the functions in Green's theorem will be
A)  Continuous partial derivatives
B)  Discrete derivatives
C)  Continuous derivatives
D)  Discrete partial derivatives

Correct Answer :   Continuous partial derivatives

Explanation : The Green’s theorem states that if L and M are functions of (x,y) in an open region containing D and having continuous partial derivatives then,
∫ (F dx + G dy) = ∫∫(dG/dx – dF/dy)dx dy, with path taken anticlockwise.

66 .
Which of the following is not an application of Green's theorem?
A)  Area surveying
B)  Volume of plane figures
C)  Centroid of plane figures
D)  Solving two dimensional flow integrals

Correct Answer :   Volume of plane figures

Explanation : In physics, Green’s theorem is used to find the two dimensional flow integrals. In plane geometry, it is used to find the area and centroid of plane figures.

67 .
Applications of Green's theorem are meant to be in
A)  One dimensional
B)  Two dimensional
C)  Three dimensional
D)  Four dimensional

Correct Answer :   Two dimensional

Explanation : Since Green’s theorem converts line integral to surface integral, we get the value as two dimensional. In other words the functions are variable with respect to x,y, which is two dimensional.

68 .
The Green's theorem can be related to which of the following theorems mathematically?
A)  Stoke’s theorem
B)  Euler’s theorem
C)  Leibnitz’s theorem
D)  Gauss divergence theorem

Correct Answer :   Stoke’s theorem

Explanation : The Green’s theorem is a special case of the Kelvin- Stokes theorem, when applied to a region in the x-y plane. It is a widely used theorem in mathematics and physics.

69 .
The transmitting antennas for lower frequencies (below 500 kHz) are generally
A)  Parabolic reflector type
B)  Horizontal suspended wire type
C)  Both (A) and (B)
D)  Vertical grounded wire type

Correct Answer :   Vertical grounded wire type

70 .
Which of the following will increase the antenna radiation efficiency?
A)  Providing insulation on conductor
B)  Use of larger section of conductor
C)  Top loading of antenna
D)  Any of the above

Correct Answer :   Top loading of antenna

71 .
According to maximum power transfer theorem, the maximum power is absorbed by one network from another network when
A)  The impedance of one is equal to that of the other
B)  The impedance of one is the complex conjugate of the other
C)  The impedance of one of the networks is half that of the other
D)  None of the above

Correct Answer :   The impedance of one is the complex conjugate of the other

72 .
A square corner reflector is used in which of the following?
A)  TV broadcast
B)  Radio astronomy
C)  Point-to-point communication
D)  All of the above

Correct Answer :   All of the above

73 .
In an impedance smith chart, a clockwise movement along a constant resistance circle gives rise to
A)  Decrease in the value of reactance
B)  An increase in the value of reactance
C)  No change in the reactance value
D)  No change in the impedance value

Correct Answer :   An increase in the value of reactance

74 .
An open wire transmission line having a characteristic impedance of 600 ohms is terminated by a resistive load of 900 O. The standing wave ratio will be
A)  1.5
A)  
B)  2.5
B)  
C)  3.5
C)  
D)  4.5
D)  

Correct Answer :   1.5

75 .
Which of the following is multiband HF receiving antenna?
A)  Log-periodic
B)  Conical horn
C)  Square loop
D)  Folded dipole

Correct Answer :   Log-periodic

76 .
In H-plane metal plate lens the travelling wave front is
A)  Retarded
B)  Accelerated
C)  Totally retarded
D)  Neither accelerated nor retarded

Correct Answer :   Retarded

77 .
It is best to use for coupling a coaxial line to a parallel wire transmission line.
A)  Tee
B)  Balun
C)  Slotted line
D)  Directional Coupler

Correct Answer :   Balun

78 .
In a perfect conductor the incident and reflected wave combine to produce
A)  A stronger reflected wave
B)  A stronger incident wave
C)  A standing wave which is not progressing
D)  None of the above

Correct Answer :   A standing wave which is not progressing

79 .
In case of surface waves the field strength at a point is directly proportional to
A)  Wave frequency
B)  Antenna height
C)  Current of the antenna
D)  Distance of the point from the antenna

Correct Answer :   Distance of the point from the antenna

80 .
The radiation pattern of Hertzian dipole in the plane perpendicular to dipole is a
A)  Null
B)  Circle
C)  Figure of eight
D)  None of the above

Correct Answer :   Circle

81 .
Which of the following represents ohms law
A)   V = RI
B)   J = σE
C)   I = GV
D)   All of the above

Correct Answer :   All of the above

Explanation :

82 .
Conductor is static and the field is varying then emf will be induced. This principle is called
A)  virtually induced emf.
B)  static induced emf.
C)  dynamically induced emf.
D)  None of the above

Correct Answer :   static induced emf.

Explanation : According to the Faraday's law of electromagnetic induction principle, the emf will be induced whenever conductor cuts a varying field or vice versa. The emf will be induced when an alternating magnetic field cuts the rotor conductor.

83 .
As a result of reflection from a plane conducting wall, electromagnetic waves acquire an apparent velocity greater than the velocity of light in space. This is called the
A)  phase velocity.
A)  
B)  group velocity.
B)  
C)  normal velocity.
C)  
D)  velocity of propagation.
D)  

Correct Answer :   phase velocity.

Explaination : The phase velocity of a wave is the rate at which the phase of the wave propagates in space. This is the speed at which the phase of any one frequency component of the wave travels. Basically, the speed of this velocity is greater than the velocity of light in space.

84 .
Inside a hollow conducting sphere
A)  electric field is zero.
B)  electric field is a non zero constant.
C)  electric field changes with distance from the center of the sphere.
D)  electric field changes with magnitude of the charge given to the conductor.

Correct Answer :   electric field is zero.

Explanation : For any conducting sphere, the charge enclosed is zero and hence, the electric field inside it is zero. This is an application of the Gauss Law. In fact Gaussian surface includes no charges inside it.

85 .
A conductor of length L has current I passing through it, when it is placed parallel to strong magnetic field. The force experienced by the conductor will be
A)  BIL
B)  BL²I
C)  BI²L.
D)  zero.

Correct Answer :   zero.

Explanation : The force can be found with the given expression F = I × L × B × sinθ and θ is the angle between I and B. When that current carrying conductor is placed parallel to the magnetic field, then the angle between current and magnetic field is zero. So, sinθ = sin0° = 0. Hence, the force experienced by the conductor is zero.

86 .
For F1 layer the maximum ionic density is 2.3 x 104 electrons per cc. The critical frequency for this layer will be
A)  1.36 MHz
A)  
B)  13.6 MHz
B)  
C)  136 MHz
C)  
D)  1360 MHz
D)  

Correct Answer :   13.6 MHz

87 .
The phase angle corresponding to λ/4 in a standing-wave pattern is
A)  30°
B)  90°
C)  135°
D)  180°

Correct Answer :   90°

88 .
A hollow rectangular waveguide has dimensions a = 2b. Calculate the amount of attenuation, if the frequency is 3 GHz, and b = 1 cm.
A)  47.33
B)  49
C)  50
D)  50.33

Correct Answer :   47.33

Explanation :

89 .
A plane electromagnetic wave travels in dielectric medium of relative permittivity 9. Relative to free space, the velocity of propagation in the dielectric is
A)  unchanged
A)  
B)  increased by a factor of 3
B)  
C)  increased by a factor of 9
C)  
D)  reduced by a factor of 1/3
D)  

Correct Answer :   reduced by a factor of 1/3

90 .
Consider a loss less antenna with a directive gain of + 6 dB. If 1 mW of power is fed to it the total power radiated by the antenna will be
A)  1/4 mW
B)  1 mW
C)  4 mW
D)  7 mW

Correct Answer :   4 mW

Explanation :

91 .
Which of the following should dominant wave have?
A)  Highest cut off frequency
B)  No attenuation
C)  Lowest cut off frequency
D)  No phase shift

Correct Answer :   Lowest cut off frequency

Explanation : Lowest cut off frequency or highest wave-length in a waveguide gives dominant modes.

92 .
Calculate the wave impedance for TM mode in rectangular waveguide for dominant mode at 3 GHz having
A)  (120π) Ω
B)  226 Ω
C)  377 Ω
D)  629 Ω

Correct Answer :   226 Ω

Explanation :

93 .
For a 400 kHz transmission line having L = 0.5 mH/km, C = 0.08 mF and negligible R and G, the value of propagation constant P will be
A)  15.9 radians/km
A)  
B)  31.8 radians/km
B)  
C)  63.6 radians/km
C)  
D)  105.4 radians/km
D)  

Correct Answer :   15.9 radians/km

Explaination :

94 .
The Depth of penetration of EM wave in medium having conductivity σ at a frequency of 1 MHz is 25 cm. The depth of penetration at a frequency of 4 MHz will be
A)  6.25 cm
A)  
B)  12.50 cm
B)  
C)  50 cm
C)  
D)  100 cm
D)  

Correct Answer :   12.50 cm

Explaination :

95 .
What is the characteristic impedance at 10 MHz?
A)  .547 Ω
B)  5.47 Ω
C)  54.7 Ω
D)  547.7 Ω

Correct Answer :   547.7 Ω

96 .
A rectangular waveguide measures 3 x 4.5 cm internally and has a 10 GHz signal propagated in it. Calculate the wave impedance for dominant mode.
A)  1.3 π
A)  
B)  12 π
B)  
C)  120 π
C)  
D)  130 π
D)  

Correct Answer :   1.3 π

97 .
Calculate wave impedance for TE mode
A)  160 Ω
B)  226 Ω
C)  (377)Ω
D)  629 Ω

Correct Answer :   629 Ω

Explanation :

98 .
In a 100 turn coil, if the flux through each turn is (t3 - 2t)mWb, the magnitude of the induced emf in the coil at a time of 4 sec is
A)  4.6 V
A)  
B)  5.6 V
B)  
C)  46 mV
C)  
D)  56 mV
D)  

Correct Answer :   4.6 V

Explaination :

99 .
A parallel polarized wave is incident from air into paraffin having relative permittivity 3, the value of its Brewster angle is
A)  0°
B)  30°
C)  45°
D)  60°

Correct Answer :   60°

100 .
In a conductor which of the following relations hold good?
A)  ∇ . D = r
B)  ∇ x D = r
C)  ∇ x D = 0
D)  ∇ . D = 0

Correct Answer :   ∇ x D = 0

Explanation : Inside a conductor free charge is zero, hence, ∇ x D = 0.

101 .
The radiation resistance of a λ/16 wire dipole in free space will be nearly
A)  30 Ω
B)  13 Ω
C)  3 Ω
D)  1 Ω

Correct Answer :   30 Ω

102 .
Find the noise factor for an antenna at 27°C with equivalent noise temperature 30°K
A)  300
B)  100
C)  20
D)  1.1

Correct Answer :   1.1

Explanation :

103 .
Characteristic impedance of a transmission line is 50 Ω. Input impedance of the open circuited line.
Zoc = 100 + J150 Ω. When transmission line is short circuited, then value of the input impedance will be
A)  50 Ω
A)  
B)  100 + J150 Ω
B)  
C)  7.69 - J11.54 Ω
C)  
D)  7.69 + J11.54Ω
D)  

Correct Answer :   7.69 - J11.54 Ω

Explaination :

104 .
A material has conductivity of 10-2 mho/m and a relative permittivity of 4. The frequency at which conduction current in the medium is equal to displacement current is
A)  45 MHz
A)  
B)  90 MHz
B)  
C)  450 MHz
C)  
D)  900 MHz
D)  

Correct Answer :   45 MHz

Explaination :

105 .
A transmission line is feeding 1 watt of power to a horn antenna having a gain of 10 dB. The antenna is matched to the transmission line. The total power radiated by the horn antenna into the free space is
A)  0.01 watt
A)  
B)  0.1 watt
B)  
C)  1 watt
C)  
D)  10 watt
D)  

Correct Answer :   10 watt

106 .
An end fire array consisting of several half-wave lengths of directive gain 40, then find the width of major lobe
A)  50
A)  
B)  60
B)  
C)  51.25
C)  
D)  None of the above
D)  

Correct Answer :   51.25

Explaination :

107 .
A uniform plane EM wave incident normally on a plane surface of a dielectric material is reflected with a VSWR of 3. What percentage of incident power that is reflected?
A)  10%
A)  
B)  25%
B)  
C)  50%
C)  
D)  75%
D)  

Correct Answer :   25%

Explaination :

108 .
Poynting vector is associated with which of the following?
A)  Flux in magnetic field
B)  Charge in electrostatic field
C)  Current in electrostatic field
D)  Power flow in electromagnetic

Correct Answer :   Power flow in electromagnetic

Explanation : P = E x H

109 .
If wave of critical frequency 30 MHz is departing at an angle of 60°, then the MUF is given to be
A)  10 MHz
B)  15 MHz
C)  30 MHz
D)  60 MHz

Correct Answer :   60 MHz

Explanation :

MUF = fc sec θ

110 .
A 10 GHz signal propagates in a waveguide with a phase velocity of 4 x 108 m/s. If the signal produces standing wave in the guide, then the distance between successive minimal will be
A)  10 mm
A)  
B)  20 mm
B)  
C)  30 mm
C)  
D)  40 mm
D)  

Correct Answer :   20 mm

Explaination :

111 .
A transmission line of characteristic impedance z0 = 50 Ω. Phase Velocity = 2 x 108 m/sec, and length l = 1 m is terminated by a load z1 = (30 - j 40) ohms. The input impedance of the line for a frequency of 100 MHz will be
A)  (50 - j 40) Ω
A)  
B)  (30 - j 40) Ω
B)  
C)  (50 + j x 40) Ω
C)  
D)  (30 + j x 40) Ω
D)  

Correct Answer :   (30 - j 40) Ω

Explaination :

112 .
A transmission line has characteristics impedance of (75 + j 0.01) Ω and is terminated in a load impedance of (70 + j 50) Ω. The transmission coefficient will be
A)  0.08 + j 0.32
A)  
B)  1.32 + j 1.38
B)  
C)  1.70 - j 2.97
C)  
D)  1.08 + j 0.32
D)  

Correct Answer :   1.08 + j 0.32

Explaination :

113 .
A TV. transmitting aerial is fixed on top of a 150 metre tower located on a mountain 1200 m height. The range of transmitter is
A)  51 km
A)  
B)  51 m
B)  
C)  152 km
C)  
D)  152 m
D)  

Correct Answer :   152 km

Explaination :

114 .
A vertical wire of 1 meter length carries a current of 1 A at 10 MHz. The total radiated power is nearly
A)  0.13 W
B)  0.88 W
C)  7.3 W
D)  73 W

Correct Answer :   73 W

Explanation :

P = I2 . R => (1)2 . 73 => 73 watt.

Here, vertical wire will be considered as dipole.

115 .
The length of half-wave antenna is at 30 MHz
A)  2.5 meter
B)  5 meter
C)  10 meter
D)  100 meter

Correct Answer :   5 meter

Explanation :

116 .
Beamwidth (between first nulls) will be for an antenna at 3 MHz with directivity of 100
A)  60°
B)  70°
C)  140°
D)  210°

Correct Answer :   140°

Explanation :

117 .
Calculate the wave number in waveguide having dimensions 4 x 2 cm at 3 GHz
A)  0
B)  6.28
C)  8.4
D)  62.8

Correct Answer :   62.8

Explanation :

118 .
A dipole antenna of λ/8 length has an equivalent total loss resistance of 1.5 Ω. The efficiency of the antenna is
A)  0.89159%
B)  8.9159%
C)  89.159%
D)  891.59%

Correct Answer :   89.159%

Explanation :

119 .
The I/P impedance of a short circuited quarter wave long transmission line is
A)  purely reactive
B)  purely resistive
C)  depend on the characteristic impedance of the line
D)  None of the above

Correct Answer :   None of the above

Explanation :

120 .
The force between two long parallel conductors is inversely proportional to
A)  distance between the conductors.
B)  radius of conductors.
C)  current in one conductor.
D)  product of current in two conductors.

Correct Answer :   distance between the conductors.

Explanation : If the current is flowing through the two different conductors ‘d’ distance apart, in the same direction, then the force between the two conductors is directly proportional to the product of the currents and inversely proportional to the distance between the two conductors.

121 .
Gain of an antenna with a circular aperture of diameter 4 meter at frequency of 10 GHz, with directivity 60
A)  30
B)  60
C)  90
D)  100

Correct Answer :   60

Explanation :

122 .
Polarization of a wave is
A)  direction of electric field
B)  direction of magnetic field at some fixed point in space
C)  Either (A) or (B)
D)  None of the above

Correct Answer :   direction of electric field

Explanation : Direction of electric field is to be taken as reference.

123 .
Calculate the directivity of a given linear end fire, uniform array of 20 element, each separated by λ/3
A)  10
B)  26.66
C)  30
D)  100

Correct Answer :   26.66

Explanation :

124 .
Antenna efficiency of antenna is, if radiation resistance is 370 Ω and loss resistance is 100 Ω
A)  21.27%
B)  78%
C)  80%
D)  87%

Correct Answer :   78%

Explanation :

125 .
Calculate cut off frequency for dominant mode in rectangular waveguide if dimensions are a = 2, b = 1 cm.
A)  150 GHz
B)  15 GHz
C)  7.5 GHz
D)  1.5 GHz

Correct Answer :   7.5 GHz

Explanation :

126 .
The input impedance for a half dipole if radii of both the antenna is 4 and 8 meter respectively
A)  100 Ω
B)  600 Ω
C)  650 Ω
D)  657 Ω

Correct Answer :   657 Ω

Explanation :

127 .
A rectangular waveguide measures 3 x 4.5 cm internally and has a 10 GHz signal propagated in it. Calculate the cut off frequency for dominant mode.
A)  4 GHz
B)  5 GHz
C)  7.5 GHz
D)  10 GHz

Correct Answer :   5 GHz

Explanation :

128 .
The refractive index of E layer, if angle of incidence is 30°
A)  0.5
B)  0.25
C)  0
D)  1

Correct Answer :   0.5

Explanation : μ = sin i

129 .
A transmission line having 50 Ω impedance is terminated in a load of (40 + j 30) Ω. The VSWR is
A)  j 0.033
B)  0.8.+ j 0.6
C)  1
D)  2

Correct Answer :   2

Explanation :

130 .
Two long parallel conductors carry 100 A. If the conductors are separated by 20 mm, the force per meter of length of each conductor will be
A)  0.01 N.
B)  0.1 N.
C)  1 N.
D)  100 N.

Correct Answer :   0.1 N.

Explanation :

131 .
Coulomb is the unit of which quantity?
A)  Charge
B)  Force
C)  Permittivity
D)  Field strength

Correct Answer :   Charge

Explanation : The standard unit of charge is Coulomb. One coulomb is defined as the 1 Newton of force applied on 1 unit of electric field.

132 .
Coulomb law is employed in
A)  Magnetostatics
B)  Maxwell theory
C)  Electrostatics
D)  Electromagnetics

Correct Answer :   Electrostatics

Explanation : Coulomb law is applied to static charges. It states that force between any two point charges is proportional to the product of the charges and inversely proportional to square of the distance between them. Thus it is employed in electrostatics.

133 .
Two charges 1C and -4C exists in air. What is the direction of force?
A)  Away from 1C
B)  Away from -4C
C)  From -4C to 1C
D)  From 1C to -4C

Correct Answer :   From 1C to -4C

Explanation : Since the charges are unlike, the force will be attractive. Thus the force directs from 1C to -4C.

134 .
Find the force between two charges when they are brought in contact and separated by 4cm apart, charges are 2nC and -1nC, in μN.
A)  1.44
B)  1.404
C)  2.44
D)  2.404

Correct Answer :   1.404

Explanation : Before the charges are brought into contact, F = 11.234 μN.
After charges are brought into contact and then separated, charge on each sphere is, (q1 + q2)/2 = 0.5nC
On calculating the force with q1 = q2 = 0.5nC, F = 1.404μN.

135 .
For a charge Q1, the effect of charge Q2 on Q1 will be,
A)  F1 = F2
B)  F1 = -F2
C)  F1 = F2 = 0
D)  F1 and F2 are not equal

Correct Answer :   F1 = -F2

Explanation : The force of two charges with respect with each other is given by F1 and F2. Thus F1 + F2 = 0 and F1 = -F2.

136 .
The electric field intensity is defined as
A)  Force per unit charge
B)  Force on a test charge
C)  Product of force and charge
D)  Force per unit charge on a test charge

Correct Answer :   Force per unit charge on a test charge

Explanation : The electric field intensity is the force per unit charge on a test charge, i.e, q1 = 1C. E = F/Q = Q/(4∏εr2).

137 .
Find the force on a charge 2C in a field 1V/m.
A)  0
B)  1
C)  2
D)  3

Correct Answer :   2

Explanation : Force is the product of charge and electric field.
F = q X E = 2 X 1 = 2 N.

138 .
What is the electric field intensity at a distance of 20cm from a charge 2 X 10-6 C in vacuum?
A)  250,000
A)  
B)  350,000
B)  
C)  450,000
C)  
D)  550,000
D)  

Correct Answer :   450,000

Explaination : E = Q/ (4∏εor2)
= (2 X 10-6)/(4∏ X εo X 0.22) = 450,000 V/m.

139 .
Electric field intensity due to infinite sheet of charge σ is
A)  Zero
B)  Unity
C)  σ/ε
D)  σ/2ε

Correct Answer :   σ/2ε

Explanation : E = σ/2ε.(1- cos α), where α = h/(√(h2+a2))
Here, h is the distance of the sheet from point P and a is the radius of the sheet. For infinite sheet, α = 90. Thus E = σ/2ε.

140 .
In electromagnetic waves, the electric field will be perpendicular to which of the following?
A)  Wave propagation
B)  Magnetic field intensity
C)  Both H and wave direction
D)  It propagates independently

Correct Answer :   Both H and wave direction

Explanation : In an electromagnetic wave, the electric field and magnetic field will be perpendicular to each other. Both of these fields will be perpendicular to the wave propagation.

141 .
The lines of force are said to be
A)  Real
B)  Imaginary
C)  Not significant
D)  Drawn to trace the direction

Correct Answer :   Drawn to trace the direction

Explanation : The lines drawn to trace the direction in which a positive test charge will experience force due to the main charge are called lines of force. They are not real but drawn for our interpretation.

142 .
Electric flux density in electric field is referred to as
A)  Number of flux lines
B)  Flux lines per unit area
C)  Direction of flux at a point
D)  Ratio of flux lines crossing a surface and the surface area

Correct Answer :   Ratio of flux lines crossing a surface and the surface area

Explanation : Electric flux density is given by the ratio between number of flux lines crossing a surface normal to the lines and the surface area. The direction of D at a point is the direction of the flux lines at that point.

143 .
The electric flux density is the
A)  Product of number of flux lines and permittivity
B)  Product of permittivity and electric field intensity
C)  Product of number of flux lines and permeability
D)  Product of permeability and electric field intensity

Correct Answer :   Product of permittivity and electric field intensity

Explanation : D= εE, where ε=εoεr is the permittivity of electric field and E is the electric field intensity. Thus electric flux density is the product of permittivity and electric field intensity.

144 .
Which of the following correctly states Gauss law?
A)  Electric flux is equal to charge
B)  Electric field is equal to charge density
C)  Electric flux per unit volume is equal to volume charge density
D)  Electric flux per unit volume is equal to charge

Correct Answer :   Electric flux per unit volume is equal to volume charge density

Explanation : The electric flux passing through any closed surface is equal to the total charge enclosed by that surface. In other words, electric flux per unit volume leaving a point (vanishing small volume), is equal to the volume charge density.

145 .
Find the flux density of line charge of radius (cylinder is the Gaussian surface) 2m and charge density is 3.14 units?
A)  0.25
B)  0.5
C)  0.75
D)  1

Correct Answer :   0.25

Explanation : The electric field of a line charge is given by, E = λ/(2περ), where ρ is the radius of cylinder, which is the Gaussian surface and λ is the charge density. The density D = εE = λ/(2πρ) = 3.14/(2π X 2) = 1/4 = 0.25.

146 .
If the radius of a sphere is 1/(4π)m and the electric flux density is 16π units, the total flux is given by,
A)  2
B)  3
C)  4
D)  5

Correct Answer :   4

Explanation : Total flux leaving the entire surface is, ψ = 4πr2D from Gauss law. Ψ = 4π(1/16π2) X 16π = 4

147 .
A point charge 2nC is located at origin. What is the potential at (1,0,0)?
A)  12
B)  14
C)  16
D)  18

Correct Answer :   18

Explanation : V = Q/(4πεr), where r = 1m
V = (2 X 10-9)/(4πε x 1) = 18 volts.

148 .
Six equal point charges Q = 10nC are located at 2,3,4,5,6,7m. Find the potential at origin.
A)  140.35
B)  141.35
C)  142.35
D)  143.35

Correct Answer :   143.35

Explanation : V = (1/4πεo) ∑Q/r = (10 X 10-9/4πεo)
(0.5 + 0.33 + 0.25 + 0.2 + 0.166 + 0.142) = 143.35 volts.

149 .
Find the potential of V = 60sin θ/r2 at P(3,60,25)
A)  5.774
A)  
B)  6.774
B)  
C)  7.774
C)  
D)  8.774
D)  

Correct Answer :   5.774

Explaination : V = 60sin θ/r2, put r = 3m, θ = 60 and φ = 25, V = 60 sin 60/32 = 5.774 volts.

150 .
The voltage at any point in an ac circuit will be
A)  Peak voltage
B)  RMS voltage
C)  Source voltage
D)  Average voltage

Correct Answer :   RMS voltage

Explanation : In any ac circuit, the voltage measured will not be exact maximum. In order to normalise, we assume the instantaneous voltage at any point be 70.7% of the peak value, which is called the root mean square (RMS)voltage.

151 .
The potential taken between two points across a resistor will be
A)  Zero
B)  Positive
C)  Negative
D)  Infinity

Correct Answer :   Negative

Explanation : The resistor will absorb power and dissipate it in the form of heat energy. The potential between two points across a resistor will be negative.

152 .
Gauss law can be used to compute which of the following?
A)  Permittivity
B)  Permeability
C)  Electric potential
D)  Radius of Gaussian surface

Correct Answer :   Radius of Gaussian surface

Explanation : Gauss law relates the electric flux density and the charge density. Thus it can be used to compute radius of the Gaussian surface. Permittivity and permeability are constants for a particular material.

153 .
Three charged cylindrical sheets are present in three spaces with σ = 5 at R = 2m, σ = -2 at R = 4m and σ =-3 at R = 5m. Find the flux density at R = 4.5m.
A)  1/4.5
A)  
B)  2/4.5
B)  
C)  3/4.5
C)  
D)  4/4.5
D)  

Correct Answer :   2/4.5

Explaination : The Gaussian cylinder of R = 4.5m encloses sum of charges of two cylinders (R = 2m and R = 4m).
By Gauss law, ψ = Q
D(2πRL) = σ(2πRL), D(2π X 4.5) = Q1 + Q2 = σ1(2π X 2) + σ2(2π X 4), here σ1 = 5 and σ2 = -2. We get D = 2/4.5 units.

154 .
Gauss law can be evaluated in which coordinate system?
A)  Cylinder
B)  Spherical
C)  Cartesian
D)  Depends on the Gaussian surface

Correct Answer :   Depends on the Gaussian surface

Explanation : The Gauss law exists for all materials. Depending on the Gaussian surface of the material, we take the coordinate systems accordingly. Suppose if the material is a coaxial cable, the Gaussian surface is in the form of cylinder. Thus we take Cylinder/Circular coordinate system.

155 .
Gauss law cannot be expressed in which of the following forms?
A)  Point
B)  Integral
C)  Stokes theorem
D)  Differential

Correct Answer :   Stokes theorem

Explanation : Gauss law can be expressed in differential or point form as,
Div (D)= ρv and in integral form as ∫∫ D.ds = Q = ψ . It is not possible to express it using Stoke’s theorem.

156 .
With Gauss law as reference which of the following law can be derived?
A)  Ohm’s law
B)  Coulomb’s law
C)  Ampere law
D)  Faraday’s law

Correct Answer :   Coulomb’s law

Explanation : From Gauss law, we can compute the electric flux density. This in turn can be used to find electric field intensity. We know that F = qE. Hence force can be computed. This gives the Coulomb’s law.

157 .
The electric flux density and electric field intensity have which of the following relation?
A)  Linear
B)  Nonlinear
C)  Inversely linear
D)  Inversely nonlinear

Correct Answer :   Linear

Explanation : The electric flux density is directly proportional to electric field intensity. The proportionality constant is permittivity. D=ε E. It is clear that both are in linear relationship.

158 .
Find the electric potential for an electric field 3units at a distance of 2m.
A)  4
B)  6
C)  9
D)  3/2

Correct Answer :   6

Explanation : The electric field intensity is the ratio of electric potential to the distance. E = V/d. To get V = E X d = 3 X 2 = 6units.

159 .
Find the work done moving a charge 2C having potential V = 24volts is
A)  12
B)  24
C)  36
D)  48

Correct Answer :   48

Explanation : The work done is the product of charge and potential.
W = Q X V = 2 X 24 = 48 units.

160 .
Calculate the capacitance of a material in air with area 20 units and distance between plates is 5m.
A)  3.536nF
B)  3.536pF
C)  35.36pF
D)  35.36nF

Correct Answer :   35.36pF

Explanation : The capacitance of any material is given by, C = εA/d, where ε = εoεr is the permittivity in air and the material respectively. Thus C = 1 X 8.854 X 10-12 X 20/5 = 35.36pF.

161 .
Find the inductance of a coil with permeability 3.5, turns 100 and length 2m. Assume the area to be thrice the length.
A)  94.131H
A)  
B)  94.131mH
B)  
C)  131.94H
C)  
D)  131.94mH
D)  

Correct Answer :   131.94mH

Explaination : The inductance is given by L = μ N2A/l, where μ= μoμr is the permeability of air and the material respectively. N = 100 and Area = 3 X 2 = 6. L = 4π X 10-7 X 1002 X 6/2 = 131.94mH

162 .
Find the current density of a material with resistivity 20 units and electric field intensity 2000 units.
A)  100
B)  200
C)  300
D)  400

Correct Answer :   100

Explanation : The current density is given by J = σ E, where σ is the conductivity. Thus resistivity ρ = 1/σ. J = E/ρ = 2000/20 = 100 units.

163 .
Find the current in a conductor with resistance 2 ohm, electric field 2 units and distance 100cm.
A)  1A
B)  10A
C)  10mA
D)  100mA

Correct Answer :   1A

Explanation : We know that E = V/d. To get potential, V = E X d = 2 X 1 = 2 volts. From Ohm’s law, V = IR and current I = V/R = 2/2 = 1A.

164 .
In electric fields, D= ε E. The correct expression which is analogous in magnetic fields will be
A)  A = μ B
B)  B = μ H
C)  H = μ A
D)  H = μ B

Correct Answer :   B = μ H

Explanation :  In electric fields, the flux density is a product of permittivity and field intensity. Similarly, for magnetic fields, the magnetic flux density is the product of permeability and magnetic field intensity, given by B= μ H.

165 .
Find the force on a conductor of length 12m and magnetic flux density 20 units when a current of 0.5A is flowing through it.
A)  60
A)  
B)  120
B)  
C)  180
C)  
D)  200
D)  

Correct Answer :   120

Explaination : The force on a conductor is given by F = BIL, where B = 20, I = 0.5 and L = 12. Force F = 20 X 0.5 x 12 = 120 N.

166 .
Calculate the power of a material with electric field 100 units at a distance of 10cm with a current of 2A flowing through it.
A)  10
A)  
B)  20
B)  
C)  30
C)  
D)  40
D)  

Correct Answer :   20

Explaination : Power is defined as the product of voltage and current.
P = V X I, where V = E X d. Thus P = E X d X I = 100 X 0.1 X 2 = 20 units.

167 .
The electrostatic energy in an electric field does not depend on which of the following?
A)  Flux lines
B)  Permittivity
C)  Applied electric field
D)  Magnitude of charges

Correct Answer :   Applied electric field

Explanation : The energy in an electric field directly magnitude of charges. Thus electric field and flux density are also dependent. But the applied field affects only the polarisation and it is independent of the energy in the field.

168 .
Calculate the energy in an electric field with permittivity of 56 and field intensity of 36π(in μJ)
A)  3.16
B)  5.16
C)  7.16
D)  9.16

Correct Answer :   3.16

Explanation : The energy in an electric field is given by, W = 0.5 x D x E. Since D = εE, we get W = 0.5 x ε x E2. On substituting the data, we get 3.16 microjoule.

169 .
Equipotential surface is a
A)  Real surface
B)  Complex surface
C)  Imaginary surface
D)  Not existing surface

Correct Answer :   Imaginary surface

Explanation : Equipotential surface is an imaginary surface in an electric field of a given charge distribution in which all the points on the surface are at the same electric potential.

170 .
If the electric potential is given, which of the following cannot be calculated?
A)  Electrostatic energy
B)  Permittivity
C)  Electric flux density
D)  Electric field intensity

Correct Answer :   Electrostatic energy

Explanation : Using potential, we can calculate electric field directly by gradient operation. From E, the flux density D can also be calculated. Thus it is not possible to calculate energy directly from potential.

171 .
Superconductors exhibit which of the following properties?
A)  Polarisation
B)  Diamagnetism
C)  Ferrimagnetism
D)  Ferromagnetism

Correct Answer :   Diamagnetism

Explanation : Since superconductors have very good conductivity at low temperatures (σ->∞), they have nearly zero resistivity and exhibit perfect diamagnetism.

172 .
Ceramic materials possess which of the following properties?
A)  Rigid and low dielectric constant
B)  Brittle and low dielectric constant
C)  Rigid and high dielectric constant
D)  Brittle and high dielectric constant

Correct Answer :   Brittle and high dielectric constant

Explanation : Ceramic materials are generally brittle. Since these materials are used in capacitors, they have higher dielectric constant than polymer. With respect to energy, they possess high electrostatic energy due to very high dielectric constant (W α ε).

173 .
Debye is the unit used to measure
A)  Permittivity
B)  Susceptibility
C)  Electric dipole moment
D)  Magnetic dipole moment

Correct Answer :   Electric dipole moment

174 .
Which of the following are conductors?
A)  Mercury
B)  Plastics
C)  Rubber
D)  Ceramics

Correct Answer :   Mercury

Explanation : Normally, metals are said to be good conductors. Here mercury is the only metal (which is in liquid form). The other options are insulators.

175 .
Conduction in metals is due to
A)  Holes only
B)  Electrons only
C)  Electrons and holes
D)  Applied electric field

Correct Answer :   Electrons only

Explanation : Conduction in metals is only due to majority carriers, which are electrons. Electrons and holes are responsible for conduction in a semiconductor.

176 .
Find the band gap energy when a light of wavelength 1240nm is incident on it.
A)  1eV
B)  2eV
C)  3eV
D)  4eV

Correct Answer :   1eV

Explanation : The band gap energy in electron volt when wavelength is given is, Eg = 1.24(μm)/λ = 1.24 x 10<sup>-6</sup>/1240 x 10<sup>-9</sup> = 1eV.

177 .
Alternating current measured in a transmission line will be
A)  Zero
B)  Peak value
C)  Average value
D)  RMS value

Correct Answer :   RMS value

Explanation : The instantaneous current flowing in a transmission line, when measured using an ammeter, will give RMS current value. This value is 70.7% of the peak value. This is because, due to oscillations in AC, it is not possible to measure peak value. Hence to normalise, we consider current at any time in a line will be the RMS current.

178 .
The current in a metal at any frequency is due to
A)  Displacement current
B)  Both conduction and displacement current
C)  Conduction current
D)  Neither conduction nor displacement current

Correct Answer :   Conduction current

Explanation : At any frequency, the current through the metal will be due to conduction current. Only at high frequencies and when medium is air, the conduction is due to displacement current. Thus in general the current in metal is due to conduction current, which depends on the mobility of the carriers.

179 .
Find the conduction current density when conductivity of a material is 500 units and corresponding electric field is 2 units.
A)  250
B)  500
C)  1000
D)  2000

Correct Answer :   1000

180 .
Calculate the convection current when electron density of 200 units is travelling at a speed of 12m/s.
A)  2880
B)  2400
C)  16.67
D)  0.06

Correct Answer :   2400

Explanation : The convection current density is given by, J = ρeV
J = 200 X 12= 2400 units.

181 .
Identify a good dielectric.
A)  Iron
B)  Ceramics
C)  Plastic
D)  Magnesium

Correct Answer :   Ceramics

Explanation : Iron and magnesium are metals. Hence they need not be considered. Both ceramics and plastic are insulators. But dielectric constant is more for ceramics always. Hence ceramics is the best dielectric.

182 .
A dielectric can be made a conductor by
A)  Heating
B)  Doping
C)  Freezing
D)  Compression

Correct Answer :   Heating

Explanation : On increasing the temperature, the free electrons in an insulator can be promoted from valence to conduction band. Gradually, it can act as a conductor through heating process. This condition is called dielectric breakdown, wherein the insulator loses its dielectric property and starts to conduct.

183 .
Find the dielectric constant for a material with electric susceptibility of 4.
A)  3
B)  5
C)  8
D)  16

Correct Answer :   5

Explanation : The electric susceptibility is given by χe = εr – 1. For a susceptibility of 4, the dielectric constant will be 5. It has no unit.

184 .
For a dielectric which of the following properties hold good?
A)  They can never become a superconductor
B)  They are superconductors at high temperatures
C)  They are superconductors at low temperatures
D)  They have very less dielectric breakdown voltage

Correct Answer :   They are superconductors at low temperatures

Explanation : Superconductors are characterised by diamagnetism behaviour and zero resistivity, which true for a dielectric. They occur only at low temperature. Thus a dielectric can become a superconductor at low temperatures with very high dielectric breakdown voltage.

185 .
The magnetic field which destroys the superconductivity is called
A)  Critical field
B)  Ferrimagnetic field
C)  Diamagnetic field
D)  Ferromagnetic field

Correct Answer :   Critical field

Explanation : Critical field is that strong magnetic field which can destroy the superconductivity of a material. The temperature at which this occurs is called transition temperature.

186 .
The magnetic susceptibility in a superconductor will be
A)  Zero
B)  Infinity
C)  Positive
D)  Negative

Correct Answer :   Negative

Explanation : Due to perfect diamagnetism in a superconductor, its magnetic susceptibility will be negative. This phenomenon is called Meissner effect.

187 .
Find the conductivity of a material with conduction current density 100 units and electric field of 4 units.
A)  25
B)  400
C)  1600
D)  1800

Correct Answer :   25

Explanation : The conduction current density is given by, Jc = σE. To get conductivity, σ = J/E = 100/4 = 25 units.

188 .
Calculate the displacement current density when the electric flux density is 20sin 0.5t.
A)  10sin 0.5t
B)  10cos 0.5t
C)  20sin 2t
D)  20cos 2t

Correct Answer :   10cos 0.5t

Explanation : The displacement current density is given by, Jd = dD/dt.
Jd = d(20sin 0.5t)/dt = 20cos 0.5t (0.5) = 10cos 0.5t.

189 .
Calculate the frequency at which the conduction and displacement currents become equal with unity conductivity in a material of permittivity 2.
A)  9 GHz
A)  
B)  18 GHz
B)  
C)  24 GHz
C)  
D)  36 GHz
D)  

Correct Answer :   9 GHz

Explaination : When Jd = Jc , we get εωE = σE. Thus εo(2∏f) = σ. On substituting conductivity as one and permittivity as 2, we get f = 9GHz.

190 .
The ratio of conduction to displacement current density is referred to as
A)  Dielectric constant
B)  Attenuation constant
C)  Loss tangent
D)  Propagation constant

Correct Answer :   Loss tangent

Explanation : Jc /Jd is a standard ratio, which is referred to as loss tangent given by σ /ε ω. The loss tangent is used to determine if the material is a conductor or dielectric.

191 .
If the loss tangent is very less, then the material will be a
A)  Insulator
B)  Conductor
C)  Lossless dielectric
D)  Lossy dielectric

Correct Answer :   Lossless dielectric

Explanation : If loss tangent is less, then σ /ε ω <<1. This implies the conductivity is very poor and the material should be a dielectric. Since it is specifically mentioned very less, assuming the conductivity to be zero, the dielectric will be lossless (ideal).

192 .
In good conductors, the electric and magnetic fields will be
A)  45 in phase
B)  45 out of phase
C)  90 in phase
D)  90 out of phase

Correct Answer :   45 out of phase

Explanation : The electric and magnetic fields will be out of phase by 45 in good conductors. This is because their intrinsic impedance is given by η = √(ωμ/σ) X (1+j). In polar form we get 45 out of phase.

193 .
In free space, which of the following will be zero?
A)  Conductivity
B)  Resistivity
C)  Permittivity
D)  Permeability

Correct Answer :   Conductivity

Explanation : In free space, ε = ε0 and μ = μ0. The relative permittivity and permeability will be unity. Since the free space will contain no charges in it, the conductivity will be zero.

194 .
If the intrinsic angle is 20, then find the loss tangent.
A)  tan 20
B)   tan 40
C)  tan 60
D)  tan 80

Correct Answer :   tan 40

Explanation : The loss tangent is given by tan 2θn, where θn = 20. Thus the loss tangent will be tan 40.

195 .
The intrinsic impedance of free space is given by
A)  272 ohm
B)  377 ohm
C)  412 ohm
D)  740 ohm

Correct Answer :   377 ohm

Explanation : The intrinsic impedance is given by η = √(μo/εo) ohm. Here εo = 8.854 x 10-12 and μo = 4π x 10-7.
On substituting the values, we get η = 377 ohm.

196 .
The best definition of polarisation is
A)  Orientation of dipole moments
B)  Change in polarity of every dipole
C)  Orientation of dipoles in random direction
D)  Electric dipole moment per unit volume

Correct Answer :   Electric dipole moment per unit volume

Explanation : The polarisation is defined mathematically as the electric dipole moment per unit volume. It is also referred to as the orientation of the dipoles in the direction of applied electric field.

197 .
Polarizability is defined as the
A)  Ratio of dipole moment to electric field
B)  Ratio of electric field to dipole moment
C)  Product of dipole moment and electric field
D)  Product of dielectric constant and dipole moment

Correct Answer :   Ratio of dipole moment to electric field

Explanation : Polarizability is a constant that is defined as the ratio of elemental dipole moment to the electric field strength.

198 .
Identify which type of polarisation depends on temperature.
A)  Ionic
B)  Electronic
C)  Orientational
D)  Interfacial

Correct Answer :   Orientational

Explanation : The electronic, ionic and interfacial polarisation depends on the atoms which are independent with respect to temperature. Only the orientational polarisation is dependent on the temperature and is inversely proportional to it.

199 .
In isotropic materials, which of the following quantities will be independent of the direction?
A)  Polarisation
B)  Permeability
C)  Permittivity
D)  Polarizability

Correct Answer :   Permittivity

Explanation : Isotropic materials are those with radiate or absorb energy uniformly in all directions (eg. Isotropic antenna). Thus it is independent of the direction.

200 .
The total polarisation of a material is the
A)  Product of all types of polarisation
B)  Sum of all types of polarisation
C)  Orientation directions of the dipoles
D)  Total dipole moments in the material

Correct Answer :   Sum of all types of polarisation

Explanation : The total polarisation of a material is given by the sum of electronic, ionic, orientational and interfacial polarisation of the material.

201 .
Solids do not have which type of polarisation?
A)  Ionic
B)  Interfacial
C)  Electronic
D)  Orientational

Correct Answer :   Interfacial

Explanation : Solids possess permanent dipole moments. Moreover they do not have junction like semiconductors. Thus, solids neglect the interfacial and space charge polarisation. They possess only electronic, ionic and orientational polarisations.

202 .
Which of the following is not an example of elemental solid dielectric?
A)  Silicon
B)  Sulphur
C)  Diamond
D)  Germanium

Correct Answer :   Silicon

Explanation : Elemental solid dielectrics are the materials consisting of single type of atoms. Such materials have neither ions nor permanent dipoles and possess only electronic polarisation. Its examples are diamond, sulphur and germanium.

203 .
Compute the refractive index when the dielectric constant is 256 in air.
A)  16
B)  64
C)  256
D)  2562

Correct Answer :   16

Explanation : By Maxwell relation, εr = n2, where εro is the dielectric constant at optical frequencies and n is the refractive index.For the given dielectric constant we get n = 16.

204 .
The continuity equation is a combination of which of the two laws?
A)  Ohm’s law and Gauss law
B)  Ohm’s law and Ampere law
C)  Ampere law and Gauss law
D)  Maxwell law and Ampere law

Correct Answer :   Ampere law and Gauss law

Explanation : I = ∫ J.ds is the integral form of Ohm’s law and Div (J) = dq/dt is the Gauss law analogous to D. Through these two equations, we get Div(J) = -dρ/dt. This is the continuity equation.

205 .
Calculate the charge density for the current density given 20sin x i + ycos z j at the origin.
A)  19t
B)  -20t
C)  20t
D)  21t

Correct Answer :   21t

Explanation : Using continuity equation, the problem can be solved. Div(J) =
– dρ/dt. Div(J) = 20cos x + cos z. At origin, we get 20cos 0 + cos 0 = 21. To get ρ, on integrating the Div(J) with respect to t, the charge density will be 21t.

206 .
Compute the conductivity when the current density is 12 units and the electric field is 20 units. Also identify the nature of the material.
A)  0.6, conductor
A)  
B)  0.6, dielectric
B)  
C)  1.67, dielectric
C)  
D)  1.67, conductor
D)  

Correct Answer :   0.6, dielectric

Explaination : The current density is the product of conductivity and electric field intensity. J = σE. To get σ, put J = 12 and E = 20. σ = 12/20 = 0.6. Since the conductivity is less than unity, the material is a dielectric.

207 .
Find the electron density when convection current density is 120 units and the velocity is 5m/s.
A)  12
B)  24
C)  600
D)  720

Correct Answer :   24

Explanation : The convection current density is given by J = ρe x v. To get ρe, put J = 120 and v = 5. ρe = 120/5 = 24 units.

208 .
Find the mobility of the electrons when the drift velocity is 23 units and the electric field is 11 units.
A)  0.9
B)  1.1
C)  2.2
D)  3.2

Correct Answer :   2.2

Explanation : The mobility is defined as the drift velocity per unit electric field. Thus μe = vd/E = 23/11 = 2.1 units.

209 .
Find the resistance of a cylinder of area 200 units and length 100m with conductivity of 12 units.
A)  1/12
B)  1/24
C)  1/48
D)  1/96

Correct Answer :   1/24

Explanation : The resistance is given by R = ρL/A = L/σA. Put L = 100, σ = 12 and A = 200, we get R = 100/(12 x 200) = 1/24 units.

210 .
Calculate the potential when a conductor of length 2m is having an electric field of 12.3units.
A)  24.6
B)  26.4
C)  42.6
D)  64.2

Correct Answer :   24.6

Explanation : The electric field is given by E = V/L. To get V, put E = 12.3 and L = 2.Thus we get V = E x L = 12.3 x 2 = 24.6 units.

211 .
For a conservative field which of the following equations holds good?
A)  ∫ H.dl = 0
B)  ∫ B.dl = 0
C)  ∫ D.dl = 0
D)  ∫ E.dl = 0

Correct Answer :   ∫ E.dl = 0

Explanation : A conservative field implies the work done in a closed path will be zero. This is given by ∫ E.dl = 0.

212 .
Find the flux density at the boundary when the charge density is given by 24 units.
A)  12
B)  24
C)  48
D)  96

Correct Answer :   24

Explanation : At the boundary of a conductor- free space interface, the flux density is equal to the charge density. Thus D = ρv = 24 units.

213 .
Which component of the electric field intensity is always continuous at the boundary?
A)  Normal
B)  Vertical
C)  Tangential
D)  Horizontal

Correct Answer :   Tangential

Explanation : At the boundary of the dielectric-dielectric, the tangential component of the electric field intensity is always continuous. We get Et1 = Et2.

214 .
The electric flux density of a surface with permittivity of 2 is given by 12 units. What the flux density of the surface in air?
A)  0
B)  1/6
C)  6
D)  24

Correct Answer :   6

Explanation : The relation between electric field and permittivity is given by Dt1/Dt2 = ε1/ε2. Put Dt1 = 12, ε1 = 2 and ε2 =1, we get Dt2 = 12 x 1/ 2 = 6 units.

215 .
A wave incident on a surface at an angle 60 degree is having field intensity of 6 units. The reflected wave is at an angle of 30 degree. Find the field intensity after reflection.
A)  7.4
A)  
B)  8.4
B)  
C)  9.4
C)  
D)  10.4
D)  

Correct Answer :   10.4

Explaination : By Snell’s law, the relation between incident and reflected waves is given by, E1 sin θ1 = E2 sin θ2. Thus 6 sin 60 = E2 sin 30. We get E2 = 6 x 1.732 = 10.4 units.

216 .
Which of the following statement regarding waveguides is incorrect?
A)  At waveguide can be coupled to a coaxial cable
B)  Waveguides can handle large power at UHF and microwaves
C)  At frequencies below the cut off value the wave progresses across the waveguide after total reflections
D)  Waveguides are usually air filled hollow conducting metallic tubes for transmitting UHF and microwaves

Correct Answer :   At waveguide can be coupled to a coaxial cable

217 .
A rectangular waveguide is a
A)  Tube antenna to transmit and receive electromagnetic waves
B)  Hollow rectangular walled room carrying electromagnetic wave
C)  Rectangular conducting wire to propagate electromagnetic waves
D)  Hollow rectangular conducting tube through which electromagnetic waves can be propagat-ed

Correct Answer :   Hollow rectangular conducting tube through which electromagnetic waves can be propagat-ed

218 .
Tropospheric scatter is used with frequencies in the
A)  HF
B)  UHF
C)  VHF
D)  VLF

Correct Answer :   UHF

219 .
A Yagi antenna has a driven antenna
A)  Only
B)  With a reflector
C)  With one or more directors
D)  With a reflector and one or more directors

Correct Answer :   With a reflector and one or more directors

220 .
In case of antenna the ratio of the power radiated in the desired direction to the power radiated in the opposite direction is known as
A)  Loss coefficient
A)  
B)  Front to back ratio
B)  
C)  Transmission efficiency
C)  
D)  None of the above
D)  

Correct Answer :   Front to back ratio

221 .
The frequency range for satellite communication is
A)  3 to 30 kHz
B)  300 to 3000 kHz
C)  3000 to 30000 MHz
D)  30000 to 300000 MHz

Correct Answer :   3000 to 30000 MHz

222 .
The static electric field in a conductor is
A)  Zero
B)  Unity
C)  Infinity
D)  None of the above

Correct Answer :   Zero

223 .
Parabolic and lens antenna used at
A)  Low frequency
B)  High frequency
C)  Medium frequency
D)  Microwave frequency

Correct Answer :   Microwave frequency

224 .
The field at any point on the axis of a current carrying coil will be
A)  zero
B)  parallel to axis.
C)  perpendicular to the axis.
D)  at angle of 45° with the axis.

Correct Answer :   parallel to axis.

Explanation : A continuous current in a current carrying coil is divided into multiple current elements. Using the superposition principle and the Biot-Savarts law, each discrete element generates its own magnetic field and when it is integrated with each field that produces a resultant field and it is aligned parallel to the axis of the coil.

225 .
Two straight parallel conductors carry equal currents in opposite direction. The force between them is
A)  zero
B)  repulsive
C)  attractive
D)  None of the above

Correct Answer :   repulsive

Explanation : When two current carrying conductors are placed parallelly, there will be a force acting between them. The force is attractive if direction of currents in the conductor is same and it is repulsive if the direction of the currents is opposite. This can easily be explained by right hand rule.

226 .
The change of cross sectional area of conductor in magnetic field will affect
A)  resistance of conductor
B)  reluctance of conductor.
C)  (A) and (B) both in the same way.
D)  None of the above

Correct Answer :   (A) and (B) both in the same way.

Explanation : We know that the cross sectional area is inversely proportional to the resistance of the conductor. In magnetic circuits, reluctance is analogous to the resistance. Hence, the resistance and reluctance would be affected in the same way.

227 .
Biot-Savarts law states the relation between magnetic intensity and
A)  surface current only
B)  volume current only
C)   filament current only
D)  All of the above

Correct Answer :   All of the above

Explanation : Biot-Savarts law states that the differential magnetic field intensity dH produced at a point P by the differential current element Idl. This is the only one law is available to relate the magnetic intensity and the different type of current distribution. The given equations show the different relations between the magnetic intensity and the currents.

228 .
If the height of transmitting and receiving antenna in a LOS system are 49 meter and a 9 meter respectively then the distance up to which communication may be possible is about
A)  40 km
A)  
B)  110 km
B)  
C)  400 km
C)  
D)  1100 km
D)  

Correct Answer :   40 km

229 .
In a line VSWR of a load is 6 dB. The reflection coefficient will be
A)  0.033
B)  0.33
C)  0.66
D)  3.3

Correct Answer :   0.66

Explanation :

230 .
A rhombic antenna is a
A)  resonant antenna
B)  coupled antenna
C)  non-resonant antenna
D)  None of the above

Correct Answer :   non-resonant antenna

231 .
Diffraction of electromagnetic waves
A)  is caused by reflections from the ground
B)  arises only with the spherical wave fronts
C)  may occur around the edge of a sharp obstacle
D)  will occur when the waves pass through a large slot

Correct Answer :   may occur around the edge of a sharp obstacle

232 .
When a particular mode is excited in a waveguide, these appears an extra electric components in the direction of propagation. The resulting mode is
A)  Longitudinal
B)  Transverse magnetic
C)  Transverse electric
D)  Transverse Electromagnetic

Correct Answer :   Transverse magnetic

233 .
An antenna has a gain of 44 dB. Assuming that the main beam of the antenna is circular in cross-section the beamwidth will be
A)  0.4456°
B)  1.4456°
C)  2.4456°
D)  3.4456°

Correct Answer :   2.4456°

Explanation :

234 .
In cellphone communication base antennas are connected to other base antennas in
A)  ionospheric propagation
B)  ground wave propagation
C)  medium wave propagation
D)  line of sight communication

Correct Answer :   line of sight communication

235 .
For frequencies upto 1650 kHz __________ antenna is used
A)  yagi
B)  turnstile
C)  marconi
D)  grounded

Correct Answer :   yagi

236 .
Due to which of the following reasons, the ground wave eventually disappears, as one moves away from the transmitter?
A)  Tilting
B)  Loss of line-of-eight conditions
C)  Interference from the sky wave
D)  Maximum single hop distance limitation

Correct Answer :   Tilting

237 .
A loop antenna may be of
A)  circular shape
B)  hexagonal shape
C)  square on triangular shape
D)  Any of the above

Correct Answer :   Any of the above

238 .
The absorption of radio waves by atmosphere depends on
A)  the polarization of the waves
B)  their frequency
C)  the polarization of atmosphere
D)  their distance from the transmitter

Correct Answer :   their frequency

239 .
For transmission-line matching over range of frequencies, it is best to use a
A)  balun
B)  double stub
C)  broadband directional coupler
D)  single stub of adjustable position

Correct Answer :   double stub

240 .
Microwave signals transmitted towards the sky are
A)  strongly reflected by the ionosphere
B)  strongly absorbed by the ionosphere
C)  transmitted through the ionosphere
D)  unable to reach the ionosphere because of strong absorption in the lower atmosphere

Correct Answer :   transmitted through the ionosphere

241 .
The drawback of Daltons atomic structure is that, it says
A)  unique nature of atom.
B)  most of the volume of an atom is empty space.
C)  the atoms can neither be created nor be destroyed.
D)  None of the above

Correct Answer :   the atoms can neither be created nor be destroyed.

Explanation : The Dalton’s atomic theory deals with chemical reactions. During chemical reactions, an atom can neither be created nor be destroyed. But, in radio active reaction, new atoms can be created by dividing other atoms. Thus, this is the very big drawback of this method.

242 .
According to Coulomb’s law, the force of attraction or repulsion, between to electrical charges is
A)  directly proportional to the distance between them
B)  inversely proportional to the distance between them
C)  directly proportional to the square of the distance between them
D)  inversely proportional to the square of the distance between them.

Correct Answer :   inversely proportional to the square of the distance between them.

Explanation : Coulomb’s law states that the force of attraction or repulsion, F between two charges q1 and q2 coulombs, connected at two different points in a medium, is directly proportional to the product of their magnitude and inversely proportional to the square of distance r between them.

243 .
A metal surface with 1 meter radius and surface charge density of 20 coulombs / m2 is enclosed in a 10 m side cube. The total outward electric displacement normal to the surface of the cube is
A)  80π coulombs
A)  
B)  40π coulombs
B)  
C)  10π coulombs
C)  
D)  None of the above
D)  

Correct Answer :   80π coulombs

Explaination :

244 .
The energy stored in the magnetic field in a solenoid 30 cm long and 3 cm diameter wound with 1000 turns of wire carrying a current at 10 amp, is
A)  1.15 joule
B)  0.15 joule
C)  0.015 joule
D)  0.015 joule

Correct Answer :   0.15 joule

Explanation :

245 .
MUF is depend upon
A)  11 year sun spot cycle
B)  Height of ionospheric layer
C)  Received frequency by receiver
D)  Electron density of the ionospheric layer

Correct Answer :   Received frequency by receiver

246 .
The radiation pattern of loop antenna is
A)  Circle
B)  Elliptical
C)  Semicircle
D)  Cardoid or Limacon

Correct Answer :   Cardoid or Limacon

247 .
When a current carrying conductor is brought into magnetic field, the force that moves the conductor depends upon
A)  The value of current
B)  The weight of the conductor
C)  The direction of the conductor
D)  None of the above

Correct Answer :   The value of current

248 .
If a and b are the dimensions of waveguide then
A)  a = 3b
B)  a = 2b
C)  a = b
D)  None of the above

Correct Answer :   a = 2b

249 .
When a wave is incident from the more dense into a less dense medium at an angle equal to or exceeding the critical angle, the wave suffers total internal __________ .
A)  Refraction
A)  
B)  Reflection
B)  
C)  Transmission
C)  
D)  None of the above
D)  

Correct Answer :   Refraction

250 .
Due to which of the following reasons a lightning conductor on top of a building is made into a pointed spike?
A)  Rain drops may not collect
B)  Dust particles may not accumulate
C)  Charge per unit area becomes very high for lightening to discharge
D)  None of the above

Correct Answer :   Charge per unit area becomes very high for lightening to discharge

251 .
When the phase velocity of an EM wave depends on frequency in any medium the phenomenon is called
A)  Absorption
B)  Polarisation
C)  Scattering
D)  Dispersion

Correct Answer :   Polarisation

252 .
A satellite that simply reflect back the signals from one region of the earth to the other region is known as
A)  Passive satellite
B)  Active satellite
C)  Orbiting satellite
D)  Geostationary satellite

Correct Answer :   Passive satellite

253 .
The main disadvantage of the two-hole directional coupler is
A)  Poor directivity
B)  Low directional coupling
C)  Narrow bandwidth
D)  High standing wave ratio

Correct Answer :   Narrow bandwidth

254 .
In microwave communication links, when fading due to rain attenuation occurs then technique adopted for solving the problem would include
A)  Polarization shifting and code diversity
A)  
B)  Amplitude timing and phase correction
B)  
C)  Antenna replacement and feed correction
C)  
D)  Path diversity and frequency diversity
D)  

Correct Answer :   Path diversity and frequency diversity

255 .
The power gain of a half-wave dipole with respect to an isotropic radiator is
A)  2.15 db
B)  3 db
C)  4.15 db
D)  6 db

Correct Answer :   2.15 db

256 .
The attenuation in waveguide above to cut off frequency
A)  Zero
B)  Very low
C)  Very high
D)  Infinite

Correct Answer :   Very low

257 .
A waveguide operated below cut off frequency can be used as
A)  An isolator
B)  Phase shifter
C)  An attenuator
D)  None of the above

Correct Answer :   An attenuator

258 .
The wave in wave guide has
A)  Larger frequency than in the free space
B)  Diminishing wavelength than in the free space
C)  Group velocity inversely proportional to wavelength
D)  Larger wavelength than in the free space

Correct Answer :   Larger wavelength than in the free space

259 .
Which of the following impedance inversion is obtained?
A)  Balun transformer
B)  A quarter wave line
C)  Short-circuited stub
D)  A half wave line

Correct Answer :   A quarter wave line

260 .
Radiation intensity in a given direction is the
A)  Energy radiated per square metre
B)  Power radiated per square metre
C)  Power radiated per unit solid angle in that direction
D)  None of the above

Correct Answer :   Power radiated per unit solid angle in that direction

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