# Electromagnetics | Subject Wise

## Electromagnetics Subject wise

 Question 1
Radiation resistance of a small dipole current element of length l at a frequency of 3 GHz is 3 ohms. If the length is changed by 1%, then the percentage change in the radiation resistance, rounded off to two decimal places, is _________%.
 A Fill in the Blank Type Question
Question 1 Explanation:
 Question 2
What is the electric flux  through a quarter-cylinder of height H (as shown in the figure) due to an infinitely long line charge along the axis of the cylinder with a charge density of Q?

 A B C D
Question 2 Explanation:
 Question 3
In the table shown, List I and List II, respectively, contain terms appearing on the left-hand side and the right-hand side of Maxwell’s equations (in their standard form). Match the left-hand side with the corresponding right-hand side.

 A 1 – Q, 2 – R, 3 – P, 4 – S B 1 – Q, 2 – S, 3 – P, 4 – R C 1 – R, 2 – Q, 3 – S, 4 – P D 1 – P, 2 – R, 3 – Q, 4 – S
Question 3 Explanation:
 Question 4
A rectangular waveguide of width w and height h has cut-off frequencies for TE10 and TE11 modes in the ratio 1 :2 . The aspect ratio w/h, rounded off to two decimal places, is ____________.
 A Fill in the Blank Type Question
Question 4 Explanation:
 Question 5
Two identical copper wires W1 and W2, placed in parallel as shown in the figure, carry currents I and 2I, respectively, in opposite directions. If the two wires are separated by a distance of 4r, then the magnitude of the magnetic field  between the wires at a distance r from W1 is

 A B C D
Question 5 Explanation:
 Question 6
The dispersion equation of a waveguide, which relates the wavenumber k to the frequency ω, is . where the speed of light c = 3 × 108 m/s, and ωo is a constant. If the group velocity is 2 × 108 m/s, then the phase velocity is
 A 1.5 × 108 m/s B 2 × 108 m/s C 4.5 × 108 m/s D 3 × 108 m/s
Question 6 Explanation:
 Question 7
The solid angle subtended by the sun as viewed from the earth is f/ = 4x10-5 steradian. A microwave antenna designed to be used for studying the microwave radiation from the sun has a very narrow beam whose equivalent solid angle is approximately equal to that subtended by the sun. What is the approximate directivity, D?
 A 105 B x105 C x106 D 106
Question 7 Explanation:
Given=>σ= 4 x 10-5 , and we have to find the approximate directivity (D)
Directivity D= 4π/σ =>
=4π/(4×10−5)
=π×10−5
 Question 8
The voltage of an electromagnetic wave propagating in a coaxial cable with uniform characteristic impedance is V(l) = volts, where ‘I’ is the distance along the length of the cable in meters. is the complex propagation constant , and is the angular frequency. The absolute value of the attenuation in the cable in dB/meter is ____
 A Fill in the Blank Type Question
Question 8 Explanation:
 Question 9
Consider a wireless communication link between a transmitter and a receiver located in free space, with finite and strictly positive capacity. If the effective areas of the transmitter and the receiver antennas, and the distance between them are all doubled, and everything else remains unchanged, the maximum capacity of the wireless link
 A increases by a factor of 2 B decrease by a factor 2 C remains unchanged D decreases by a factor of
Question 9 Explanation:
C= Blog2
Channel capacity remain same.
 Question 10
An optical fiber is kept along the z direction. The refractive indices for the electric fields along x and y directions in the fiber are n x=1.5000 and n y =1.5001, respectively (n x≠ n y due to the imperfection in the fiber cross-section). The free space wavelength of a light wave propagating in the fiber is 1.5μm. If the light wave is circularly polarized at the input of the fiber, the minimum propagation distance after which it becomes linearly polarized, in centimeter, is
 A Fill in the Blank Type Question
Question 10 Explanation:
 Question 11
The expression for an electric field in free space is  where x, y, z represent the spatial coordinates, t represents time, and ω, k are constants. This electric field
 A does not represent a plane wave B represents a circular polarized plane wave propagating normal to the z-axis C represents an elliptically polarized plane wave propagating along x-y plane. D represents a linearly polarized plane wave
Question 11 Explanation:
Given
 Question 12
A half wavelength dipole is kept in the x-y plane and oriented along 45from the x-axis. Determine the direction of null in the radiation pattern for 0≤θ≤π. Here the angle θ (0≤θ≤π) is measured from the z-axis, and the angle ∅(0≤∅≤2π) is measured from the x-axis in the x-y plane.
 A Θ=90 °, ∅=45 ° B Θ=45 °, ∅=90 ° C Θ=90 °, ∅=135 ° D Θ=45 °, ∅=135 °
Question 12 Explanation:
The Correct Answer Among All the Options is A
Null occurs along axis of the antenna which is θ=90 °, ∅=45 °
 Question 13
The points and shows on the Smith chart (normalized impedance chart) in the following figure represent:
 A Open Circuit, Short Circuit, Matched Load B Open Circuit, Matched Load, Short Circuit C Short Circuit, Matched Load, Open Circuit D Short Circuit, Open Circuit, Matched Load
Question 13 Explanation:
For Short circuit z = Re(z) = Im(z) = 0 => Point "P"
For Open circuit z = ∞ => Point "R"
For Matched load z = Re(z) = 1 and Im(z) = 0 => Point "Q"
P : Short Circuit, Q : Matched Load, R : Open Circuit
 Question 14
A lossy transmission line has resistance per unit length The line is distortionless and has characteristic impendace of The attenuation constant (in Np/m, correct to three decimal places) of the line is _____________.
 A Fill in the Blank Type Question
Question 14 Explanation:
 Question 15
A uniform plane wave traveling in free space and having the electric field

is incident on a dielectric medium (relative permittivity > 1, relative permeability = 1) as shown in the figure and there is no reflected wave.

The relative permittivity (correct to two decimal places) of the dielectric medium is _____________.
 A Fill in the Blank Type Question
Question 15 Explanation:
 Question 16
The cut-off frequency of mode of an air filled rectangular waveguide having inner dimensions is twice that of the dominant. mode. When the waveguide is operated at a frequency which is 25% higher than the cut-off frequency of the dominant mode, the guide wavelength is found to be 4 cm. The value of b (in cm, correct to two decimal places) is ____________.
 A Fill in the Blank Type Question
Question 16 Explanation:
 Question 17
The distance (in meters) a wave has to propagate in a medium having a skin depth of 0.1 m so that the amplitude of the wave attenuates by 20 dB, is
 A 0.12 B 0.23 C 0.46 D 2.3
Question 17 Explanation:
Attenuation constant is related with skin depth as follows
According to given condition of 20 dB Attenuation
we can get required depth by following calculation
 Question 18
Two conducting spheres S1 and S2 of radii a and b (b>A. respectively, are placed far apart and connected by a long, thin conducting wire, as shown in the figure.

For some charge placed on this structure, the potential and surface electric field on S1 are Va and Ea and that on S2 are Vb and Eb respectively, which of the following is CORRECT?
 A and B and C and D and
Question 18 Explanation:
two spheres are joined with a conducting wire, the voltage on two spheres is same.

We know Q = CV

 Question 19
A two – wire transmission line terminates in a television set. The VSWR measured on the line is 5.8. The percentage of power that is reflected from the television set is ______
 A Fill in the Blank Type Question
Question 19 Explanation:
Percentage of power reflected is = ×100

% Power reflected =×100=49.82%
 Question 20
An electron (q1) is moving in free space with velocity towards a stationary electron (q2) far away. The closest distance that this moving electron gets to the stationary electron before the repulsive force diverts its path is _____.
[Given, mass of electron m
charge of electron , and permittivity -
]
 A Fill in the Blank Type Question
Question 20 Explanation:
Work done due to field and external agent must be zero
qV=

Answer Range : (4.55 to 5.55)
 Question 21
Standard air – filled rectangular waveguides of dimensions a = 2.29 cm and b= 1.02 cm are designed for radar applications. It is desired that these waveguides operate only in the dominant TE10 mode with the operating frequency atleast 25% above the cutoff frequency of TE10 mode but not higher than 95% of the next higher cutoff frequency. The range of the allowable operating frequency f is.
 A B C D
Question 21 Explanation:
 Question 22
The permittivity of water at optical frequencies is 1.75ε.It is found that an isotropic light source at a distance d under-water forms an illuminated circular area of radius 5m, as shown in the figure. The critical angle is θc. The value of d (in meter) is _____
 A Fill in the Blank Type Question
Question 22 Explanation:
 Question 23
Concentric spherical shells of radii 2 m, 4 m, and 8 m carry uniform surface charge densities of respectively. The value of required to ensure that the electric flux density at radius 10 m is ______.
 A Fill in the Blank Type Question
Question 23 Explanation:
Consider a Gaussian surface a sphere of radius 10m
To ensure at radius 10m, the total charge enclosed by Gaussian surface is zero.
Qenc = 0
=20 x 22 - 4 x 42 -Ps x 82 = 0
Therefore, Ps = -0.25nC/m2
 Question 24
The region specified by  in cylindrical coordinates has volume of
 A Fill in the Blank Type Question
Question 24 Explanation:
 Question 25
The current density in a medium is given by

The total current and the average current density flowing through the portion of a spherical surface
are given, respectively, by
 A B C D none of these
Question 25 Explanation:
The Correct Answer Among All the Options is D

Refer the Topic Wise Question for Electrostatics Electromagnetics
 Question 26
An antenna pointing in a certain direction has a noise temperature of 50K. The ambient temperature is 290 K. The antenna is connected to a pre-amplifier that has a noise figure of 2 dB and an available gain of 40 dB over an effective bandwidth of 12 MHz. The effective input noise temperature Te for the amplifier and the noise power Paoat the output of the preamplifier, respectively, are
 A B C D
Question 26 Explanation:
 Question 27
Two lossless X-band horn antennas are separated by a distance of 200. The amplitude reflection coefficients at the terminals of the transmitting and receiving antennas are 0.15 and 0.18, respectively. The maximum directivities of the transmitting and receiving antennas (over the isotropic antenna) are 18 dB and 22 dB, respectively. Assuming that the input power in the lossless transmission line connected to the antenna is 2 W, and that the antennas are perfectly aligned and polarization matched, the power (in mW) delivered to the load at the receiver is ___.
 A Fill in the Blank Type Question
Question 27 Explanation:
Given Lossless horn antennas
ηT = ηR = 1

 Question 28
The electric field of a uniform plane wave travelling along the negative z direction is given by the following equation:

This wave is incident upon a receiving antenna placed at the origin and whose radiated electric field towards the incident wave is given by the following equation:

The polarization of the incident wave, the polarization of the antenna and losses due to the polarization mismatch are, respectively,
 A Linear, Circular (clockwise), —5dB B Circular (clockwise), Linear, —5dB C Circular (clockwise), Linear, —3dB D Elliptical, Linear, —3dB
Question 28 Explanation:

 Question 29
The far-zone power density radiated by a helical antenna is approximated as:

The radiated power density is symmetrical with respect to (I) and exists only in the upper hemisphere: is a constant. The power radiated by the antenna (in watts) and the maximum directivity of the antenna, respectively, are
 A 1.5CO, 10dB B 1.256C0, 10dB C 1.256CO. 12dB D 1.5CO, 12dB
Question 29 Explanation:
 Question 30
The electric field component of a plane wave traveling in a lossless dielectric medium is given by V/m. The wavelength (in m) for the wave is ___________.
 A Fill in the Blank Type Question
Question 30 Explanation:
 Question 31
A vector is given by . Which one of the following statements is TRUE?
 A is solenoidal, but not irrotational B is irrotational, but not solenoidal C is neither solenoidal nor irrotational D is both solenoidal and irrotational
Question 31 Explanation:
The Correct Answer Among All the Options is A

For solenoidal

is solenoidal
 Question 32
The longitudinal component of the magnetic field inside an air-filled rectangular waveguide made of a perfect electric conductor is given by the following expression
(A/m)
The cross-sectional dimensions of the waveguide are given as a = 0.08 m and b = 0.033 m. The mode of propagation inside the waveguide is
 A TM12 B TM21 C TE21 D TE12
Question 32 Explanation:

Axial component is H ⇒ the propagating
Mode is TEmn, m, n can be found by

The mode of propagation is TE21.
 Question 33
The electric field intensity of a plane wave traveling in free space is given by the following expression

In this field, consider a square area 10 cm x 10 cm on a plane x + y = 1. The total time-averaged power (in mW) passing through the square area is __________.
 A Fill in the Blank Type Question
Question 33 Explanation:

Power density

Time average power

 Question 34
Consider a uniform plane wave with amplitude (E0) of 10 V/m and 1.1 GHz frequency travelling in air, and incident normally on a dielectric medium with complex relative permittivity and permeability as shown in the figure.

The magnitude of the transmitted electric field component (in V/m) after it has travelled a distance of 10 cm inside the dielectric region is ________.
 A Fill in the Blank Type Question
Question 34 Explanation:
Given,

Attenuation constant of the medium is given by

Where

At a distance of 10 cm |E| is given by
 Question 35
A uniform and constant magnetic field exists in the direction in vacuum. A particle of mass m with a small charge q is introduced into this region with an initial velocity Given that are all non-zero, which one of the following describes the eventual trajectory of the particle?
 A Helical motion in the direction. B Circular motion in the xy plane. C Linear motion in the direction. D Linear motion in the direction.
Question 35 Explanation:
 Question 36
Let the electric field vector of a plane electromagnetic wave propagating in a homogenous medium be expressed as , where the propagation constant is a function of the angular frequency . Assume that and are known and are real. From the information available, which one of the following CANNOT be determined?
 A The type of polarization of the wave. B The group velocity of the wave. C The phase velocity of the wave. D The power flux through the z = 0 plane.
Question 36 Explanation:
Option (A) The polarization is linear
Option(B)

Option(C)
Option(D) It is not possible to find the intrinsic impedance of the medium. So, it is not possible to find power flux.
 Question 37
Light from free space is incident at an angle 0, to the normal of the facet of a step-index large core optical fibre. The core and cladding refractive indices are n1 =1.5 and n2 = 1.4, respectively. The maximum value of (in degrees) for which the incident light will be guided in the core of the fibre is ______
 A Fill in the Blank Type Question
Question 37 Explanation:
Given n1 = 1.5, n2 = 1.4
The maximum angle over which the incident light rays entering the fiber is called acceptance angle, Θi
 Question 38
The parallel-plate capacitor shown in the figure has movable plates. The capacitor is charged so that the energy stored in it is E when the plate separation is d. The capacitor is then isolated electrically and the plates are moved such that d the plate separation becomes 2d. At this new plate separation, what is an effect stored in the capacitor, neglecting fringing the energy?
 A 2E B C E D E/2
Question 38 Explanation:

If capacitor is electrically isolated then charge is same
We know and
If `d' is doubled then C will be C/2 and V will be 2V
Given

 Question 39
A microwave circuit consisting of lossless transmission lines T1 and T2 is shown in the figure. The plot shows the magnitude of the input reflection coefficient Γ as a function of frequency f. The phase velocity of the signal in the transmission lines is 2 × 108m/s. The length L(in meters) of T2 is_________
 A Fill in the Blank Type Question
Question 39 Explanation:
 Question 40
A positive charge q is placed at x = 0 between two infinite metal plates placed at x = −d and at x = +d respectively. The metal plates lie in the yz plane. The charge is at rest at t = 0, when a voltage +V is applied to the plate at −d and voltage −V is applied to the plate at x = +d. Assume that the quantity of the charge q is small enough that it does not perturb the field set up by the metal plates. The time that the charge q takes to reach the right plate is proportional to
 A d/V B √d/V C d/√V D √(d/V)
Question 40 Explanation:

When there is no external field,
Change at rest having potential energy only
P.E = qv
By an application of an external field, change carries acquire some kinetic energy, with velocity v.

 Question 41
If a right-handed circularly polarized wave is incident normally on a plane perfect conductor, then the reflected wave will be
 A Right-handed circularly polarized B Left-handed circularly polarized C Elliptically polarized with a tilt angle of 45 ° D Horizontally polarized
Question 41 Explanation:
If incident wave is right handed polarized then the reflected wave is left handed polarized.
 Question 42
Faraday’s law of electromagnetic induction is mathematically described by which one of the following equations?
 A B C D
Question 42 Explanation:
Differential from of Faraday’s law in given by
 Question 43
Consider an air-filled rectangular waveguide with dimensions a = 2.286 cm and b = 1.016 cm. At 10 GHz operating frequency, the value of the propagation constant (per meter) of the corresponding propagating mode is _________.
 A Fill in the Blank Type Question
Question 43 Explanation:
 Question 44
Consider an air-filled rectangular waveguide with dimensions a = 2.286 cm and b = 1.016 cm. The increasing order of the cut-off frequencies for different modes is
 A B C D
Question 44 Explanation:
 Question 45
A radar operating at 5 GHz uses a common antenna for transmission and reception. The antenna has a gain of 150 and is aligned for maximum directional radiation and reception to a target 1 km away having radar cross-section of . If it transmits 100 kW, then the received power (in )is _____.
 A Fill in the Blank Type Question
Question 45 Explanation:
 Question 46
The directivity of an antenna array can be increased by adding more antenna elements, as a larger number of elements
 A improves the radiation efficiency B increases the effective area of the antenna C results in a better impedance matching D allows more power to be transmitted by the antenna
Question 46 Explanation:
As increasing no. of antennas, increases the effective area.
Effective area ( Ae) and directivity (D) are related by,

Therefore, the directivity of an antenna array can be increased by increasing the effective area of the antenna.
 Question 47
A coaxial cable is made of two brass conductors. The spacing between the conductors is filled with Teflon (er = 2.1, tan  = 0). Which one of the following circuits can represent the lumped element model of a small piece of this cable having length z?
 A B C D
Question 47 Explanation:
It is given that

So,
G -> Conductivity of the dielectric material
Hence, conductivity is
So G = 0

Exp-2
Since Loss tangent is zero between conductors hence loss will be zero in between medium.
 Question 48
In the circuit using an ideal opamp, the 3-dB cut-off frequency (in Hz) is __________.
 A Fill in the Blank Type Question
Question 48 Explanation:
 Question 49
Consider the 3 m long lossless air-filled transmission line shown in the figure. It has a characteristic impedance of 120pW, is terminated by a short circuit, and is excited with a frequency of 37.5 MHz. What is the nature of the input impedance (Zin)?
 A Open B Short C Inductive D Capacitive
Question 49 Explanation:

Hence, input impedance is capacitive in nature.
 Question 50
The electric field of a uniform plane electromagnetic wave is

The polarization of the wave is
 A Right handed circular B Right handed elliptical C Left handed circular D Left handed elliptical
Question 50 Explanation:
 Question 51
In a source free region in vacuum, if the electrostatic potential = 2x2 + y2 + cz2, the value of constant c must be________________
 A -2 B -3 C -4 D -5
Question 51 Explanation:
Given electrostatic potential

So, the electric field is obtained as

In source free region,

Substituting equation (1), we get

or – 4 –2 – 2C = 0
or C = – 3
 Question 52
Two half-wave dipole antennas placed as shown in the figure are excited with sinusoidally varying currents of frequency 3 MHz and phase shift of π/2 between them (the element at the origin leads in phase). If the maximum radiated E-field at the point P in the x-y plane occurs at an azimuthal angle of 60o the distance d (in meters) between the antennas is ____________.
 A 25 B 30 C 50 D 100
Question 52 Explanation:
For maximum electric field, we have

Where

θ = Azimuthal angle = 60 º
α = Phase shift
Substituting these values in equation (1), we get
 Question 53
An air-filled rectangular waveguide of internal dimensions a cm × b cm(a > b) has a cutoff frequency of 6 GHz for the dominant TE10 mode. For the same waveguide, if the cutoff frequency of the TM11 mode is 15 GHz, the cutoff frequency of the TE01 mode in GHz is ___________.
 A 27 B 12.5 C 15 D 13.74
Question 53 Explanation:
 Question 54
The force on a point charge +q kept at a distance d from the surface of an infinite grounded metal plate in a medium of permittivity is
 A 0 B C D
Question 54 Explanation:
 Question 55
In spherical coordinates, let denote until vectors along the directions.
represent the electric and magnetic field components of the EM wave of large distances r from a dipole antenna, in free space. The average power (W) crossing the hemispherical shell located at
 A 45.5 B 55.5 C 65.5 D 75.5
Question 55 Explanation:
 Question 56
For a parallel plate transmission line, let v be the speed of propagation and Z be the characteristic impedance. Neglecting fringe effects, a reduction of the spacing between the plates by a factor of two results in
 A Halving of v and no change in Z B No changes in v and halving of Z C No change in both v and Z D Halving of both v and Z
Question 56 Explanation:

d distance between the two plates
so, z0 – changes, if the spacing between the plates changes.
independent of spacing between the plates
 Question 57
The input impedance of a λ/8 section of a lossless transmission line of characteristic impedance 50Ω is found to be real when the other end is terminated by a load ZL(=R + jX)Ω. If X is 30Ω, the value of R (in Ω ) is _______
 A 30 B 40 C 50 D 60
Question 57 Explanation:
 Question 58
To maximize power transfer, a lossless transmission line is to be matched to a resistive load impedance via a transformer as shown.

The characteristic impedance (in) of the transformer is _________.
 A 60.85 B 67.5 C 70.7 D 75.2
Question 58 Explanation:
Given the input impedance,
Zin = 50Ω
ZL = 100Ω
For a λ/4 transformer, the input impedance is given as
Zin = (Zo)2/ZL
Here impedance is matched by using QWT
 Question 59
Which one of the following field patterns represents a TEM wave travelling in the positive x direction?
 A B C D
Question 59 Explanation:
For TEM wave
Electric field (E), Magnetic field (H) and
Direction of propagation (P) are orthogonal to each other.
Here P = + ax
By verification

i.e. the TEM wave travelling in positive x -direction.
 Question 60
If the electric field of a plane wave is

the polarization state of the plane wave is
 A Left elliptical B Left circular C Right elliptical D Right circular
Question 60 Explanation:
 Question 61
In the transmission line shown, the impedance Zin (in ohms) between node A and the ground is _________.
 A 22.22 B 33.33 C 44.44 D 55.55
Question 61 Explanation:
 Question 62
For a rectangular waveguide of internal dimensions a × b(a > b) , the cut-off frequency for the mode is the arithmetic mean of the cut-off frequencies for mode and mode. If the value of b (in cm) is _____.
 A 1 cm B 2 cm C 4 cm D 8 cm
Question 62 Explanation:
 Question 63
Consider an air filled rectangular waveguide with a cross-section of 5 cm × 3 cm. For this waveguide, the cut-off frequency (in MHz) of mode is _________.
 A 7420 MHz B 7640 MHz C 7810 MHz D 8410 MHz
Question 63 Explanation:
 Question 64
In the following figure, the transmitter Tx sends a wideband modulated RF signal via a coaxial cable to the receiver Rx. The output impedance of Tx, the characteristic impedance of the cable and the input impedance of Rx are all real.

Which one of the following statements is TRUE about the distortion of the received signal due to impedance mismatch?
 A The signal gets distorted if irrespective of the value of B The signal gets distorted if irrespective of the value of C Signal distortion implies impedance mismatch at both ends: D Impedance mismatches do NOT result in signal distortion but reduce power transfer efficiency
Question 64 Explanation:
1. If either of ZR and ZT is matched with Zo , it will cause complete absorption of signal travelling on the line. So, for distorted signal, We have both conditions ZT ≠ Zo and ZR ≠ Zo
2. Signal distortion implies impedance mismatch at both ends. i.e.,
 Question 65
Given the vector where denote unit vectors along x, y directions, respectively. The magnitude of curl of A is ___
 A 0 B 1 C 2 D sinx
Question 65 Explanation:
 Question 66
A region shown below contains a perfect conducting half-space and air. The surface current on the surface of the perfect conductor is amperes per meter. The tangential field in the air just above the perfect conductor is
 A B C D
Question 66 Explanation:
 Question 67
Assume that a plane wave in air with an electric field V/m is incident on a non-magnetic dielectric slab of relative permittivity 3 which covers the region. Z > 0 The angle of transmission in the dielectric slab is _________________ degrees.
 A 300 B 450 C 600 D 900
Question 67 Explanation:
 Question 68
For an antenna radiating in free space, the electric field at a distance of 1 km is found to be 12mV/m. Given that intrinsic impedance of the free space is , the magnitude of average power density due to this antenna at a distance of 2 km from the antenna is________________.
 A 50.7 B 48.7 C 45.7 D 47.7
Question 68 Explanation:
 Question 69
Match column A with column B
 A B C D
Question 69 Explanation:
A Yagi–Uda antenna, commonly known as a Yagi antenna, is a directional antenna consisting of multiple parallel elements in a line Also called a "beam antenna", or "parasitic array", the Yagi is very widely used as a high-gain antenna on the HF, VHF and UHF bands. It has moderate to high gain which depends on the number of elements used, typically limited to about 20 dBi, linear polarization, unidirectional (end-fire) beam pattern with high front-to-back ratio of up to 20 dB. and is lightweight, inexpensive and simple to construct.
Refer : https://en.wikipedia.org/Uda_antenna
• Point electromagnetic source, can radiate fields in all directions equally, so isotropic.
• Dish antenna             →    highly directional
• Yagi – uda antenna  →    End fire

Figure: Yagi-uda antenna
 Question 70
The electric field (assumed to be one-dimensional) between two points A and B is shown. Let be the electrostatic potentials at A and B, respectively. The value of in Volts is _________.
 A 10 B -10 C 15 D -15
Question 70 Explanation:
 Question 71
Given If S represents the portion of the sphere x2 + y2 + z2 = 1 for z ≥ 0, then
 A 2.14 B 2.75 C 3.14 D 3.75
Question 71 Explanation:
 Question 72
Consider a vector field . The closed loop line integral can be expressed as
 A over the closed surface bounded by the loop B over the closed volume bounded by the loop C over open volume bounded by the loop D over the open surface bounded by the loop
Question 72 Explanation:
Stoke’s theorem states that the circulation a vector field around a closed path l is equal to the surface integral of the curl of over the open surface S bounded by l.
i.e.,
Here, line integral is taken across a closed path which is denoted by a small circle on the integral notation where as, the surface integral of is taken over open surface bounded by the loop.
Hence correct option is D.
 Question 73
The return loss of a device is found to be 20 dB. The voltage standing wave ratio (VSWR) and magnitude of reflection coefficient are respectively
 A 1.22 and 0.1 B 0.81 and 0.1 C – 1.22 and 0.1 D 2.44 and 0.2
Question 73 Explanation:
 Question 74
A plane wave propagation in air with V/m is incident on a perfectly conducting slab positioned at x ≤ 0. The field of the reflected wave is
 A B C D
Question 74 Explanation:

Since perfect conductor will reflect wave totally. Let reflected wave is
tangential component of incident wave is

Since at the boundary net tangential field will be zero.
For this tangential component of reflected wave and tangential component of incident wave must cancel out each other, for this

• Reflected wave will have normal component such that it will cancel out the normal component of incident wave so it will be .
• Also the direction of propagation will be in -x direction.
 Question 75
The electric field of a uniform plane electromagnetic wave in free space, along the positive x direction, is given by . The frequency and polarization of the wave, respectively, are
 A 1.2 GHz and left circular B 4 Hz and left circular C 1.2 GHz and right circular D 4 Hz and right circular
Question 75 Explanation:
 Question 76
A coacial cable with an inner diameter of 1 mm and outer diameter of 2.4 mm is field with a dielectric of relative permittivity 10.89. Given , , the characteristic impedance of the cable is
 A 330 Ω B 100 Ω C 143.2 Ω D 15.89 Ω
Question 76 Explanation:
Characteristics impedance of the co-axial cable is given by
 Question 77
The radiation pattern of an antenna in spherical co-ordinates is given by

The directivity of the antenna is
 A 10 dB B 12.6 dB C 11.5 Db D 18 dB
Question 77 Explanation:

we know that directivity D is
……(1)
F(θ) is nothing but radiation intensity u(θ, ) and is radiated power.
……(2)
above equation is written from the formula

Where dΩ is solid angle and
So from (2)

…(3)
So,

In dB directivity = 10 log10 D = 10 dB
 Question 78
A transmission line with a characteristic impedance of 100 Ω is used to match a 50 Ω section to a 200 Ω section. If the matching is to be done both at 429 MHz and 1 GHz. the length of the transmission line can be approximately
 A 82.5 cm B 1.05 m C 1.58 m D 1.75 m
Question 78 Explanation:

 Question 79
The direction of vector A is radially outward from the origin, with |A| = krn where r2 = x2 + y2 + z2 and k is a constant. The value of n for which is
 A –2 B 2 C 1 D 0
Question 79 Explanation:
|A|=krn
in spherical coordinate is

So, will be zero if will be zero and will be zero if rn+2 will be constant and this is possible if
n + 2 = 0
n = -2
 Question 80
An infinitely long uniform solid wire of radius a carries a uniform dc current of density .
The magnetic field at a distance r from the centre of the wire is proportional to
 A r for r < a and l/r2 for r > a B 0 for r a C r for r < a and 1/r for r > a D 0 for r2 for r > a
Question 80 Explanation:
We know that magnetic flux density at a distance r from the wire is

So,

So,
for r > a
 Question 81
An infinitely long uniform solid wire of radius a carries a uniform dc current of density.
A hole of radius b(b < a) is now drilled along the length of the wire at a distance d from the center of the wire as shown below.

The magnetic field inside the hole is
 A Uniform and depends only on d B Uniform and depends only on b C Uniform and depends on both b and d D Non uniform
Question 81 Explanation:
Magnetic field inside hole depends on radius of hole i.e. b and also on the location of hole from center of the conductor  i.e d. As hole has uniform cross section , magnetic field is uniform.
 Question 82
The vector RAB extends from A(1, 2, 3) to B. If the length of RAB is 10 units and its direction is given by

the coordinates of B will be
 A B C D
Question 82 Explanation:
 Question 83
What is the value for the total charge enclosed in an incremental volume of 10-9 m3 located at the origin if ?
 A 8 nC B 4 nC C 2 nC D 1 nC
Question 83 Explanation:
 Question 84
The unit vector extending from origin toward the point G(2, -2. -1) is
 A B C D
Question 84 Explanation:

0(0,0,0) & G (2,–2,–1)
 Question 85
Ground waves progress along the surface of the earth and must be polarized
 A horizontally B circularly C elliptically D vertically
Question 85 Explanation:
Ground waves are vertically polarized waves because Vertical polarization has considerably less attenuation than horizontally polarization.
 Question 86
For a lossless line terminated in a short circuit, the stationary voltage minima and maxima are separated by
 A B C D
Question 86 Explanation:
In standing waves voltage maxima are separated by λ/2
In standing waves voltage minima are separated by λ/2
Therefore voltage maxima and voltage minima are separated by λ/4
 Question 87
The characteristic impedance of an 80 cm long lossless transmission line having L = 0.25 μH/m and C = 100 pF/m will be
 A 25 Ω B 40 Ω C 50 Ω D 80 Ω
Question 87 Explanation:
Given L = 0.25 μH/m and C = 100 pF/m

As it is lossless transmission line so R=G=0
Characteristic impedance = =

= 50Ω
 Question 88
It is required to match a 200 Ω load to a 300 Ω transmission line to reduce the SWR along the line to 1. If it is connected directly to the load, the characteristic impedance of the quarterwave transformer used for this purpose will be
 A 275 Ω B 260 Ω C 245 Ω D 230 Ω
Question 88 Explanation:
= 200Ω, = 300Ω

∴ (√6 * 100 Ω) = 245Ω
 Question 89
For a standard rectangular waveguide having an aspect ratio of 2: 1 the cutoff wavelength for TM1,1 mode will be nearly
 A 0.9a B 0.7a C 0.5a D 0.3a
Question 89 Explanation:
Aspect ratio

λC11 = 0.9 a
 Question 90
The irises in the rectangular metallic waveguide may be
1) inductive
2) resistive
3) capacitive
Select the correct answer using the code given below.
 A 1, 2 and 3 B 1 and 2 only C 1 and 3 only D 2 and 3 only
Question 90 Explanation:
The irises in the metallic wave guide can be classify as
1. Inductive
2. Capacities
3. Tune circuit (LC)
In option we are seeing inductive or capacitive so Option(C) is correct
 Question 91
A 10 GHz signal is propagated in a waveguide whose wall separation is 6 cm. The greatest number of half-waves of electric intensity will be possible to establish between the two walls. The guide wavelength for this mode of propagation will be
 A 6.48 cm B 4.54 cm C 2.48 cm D 1.54 cm
Question 91 Explanation:
 Question 92
In Tem, n mode m and n are integers denoting the number of
 A the wavelengths of intensity between each pair of walls B the wavelengths of intensity between each pair of walls C the wavelengths of intensity between each pair of walls D the wavelengths of intensity between each pair of walls
Question 92 Explanation:
In TEm,n modes
m, n stands for feed connection machanism and positioning of feed.
m & n are determined by number of feed connection
and also they define number of Halfcycle between guide walls
 Question 93
Consider the following statements with reference to dipole arrays:
1) In broadside array, all the dipoles are fed in the same phase from the same source.
2) In end-fire array, the magnitude of the current in each element is same and there is no phase difference between these currents.
Which of the above statements is/are correct?
 A 1 only B 2 only C Both 1 and 2 D Neither 1 nor 2
Question 93 Explanation:
We know that E = 2Eo cos (Ψ/2)
For broad side array Qmax must be 90o or 270o
For E to be maximum Ψ = 0
Ψ = α + β d cos Q = 0
α + β d cos (90) = 0
α = 0
For end fire array Qmax must be 0o or 180o
Ψ = α + β d cos Q = 0
α + β d cos ( 0 or 180o) = 0
α = ± β d
Endfire array α = ± βd
so only statement 1 is correct
 Question 94
An antenna is fed with 200 W power. The efficiency of the antenna is 75%. If the radiation pattern of the antenna is pattern of the antenna is for (azimuth angle) and (elevation angle). =0 elsewhere
Question 94 Explanation:
The Correct Answer Among All the Options is A

= =>
Maximum radiation intensity is given by,
=> , where
Also it is given , for (azimuth angle) and (elevation angle).
For a given radiation pattern ,
=
=
=
Now, => = 225 watt/str
Refer the Topic Wise Question for Antenna Electromagnetics
 Question 95
Two communication antennas A and B, are operating at 300 MHz and other at 3 GHz respectively and having same gain, are illuminated with identical flux density of -100 dBW/m2. What is the relation between the received powers (PA : PB)?
 A 1:10 B 10:1 C 1:100 D 100:1
Question 95 Explanation:
The Correct Answer Among All the Options is D
For receiving antenna

=

=
=100:1
Refer the Topic Wise Question for Antenna Electromagnetics
 Question 96
Design a single section, quarter wave impedance transformer at 5 GHz from 3.75 cm x 2 cm guide to 3.75 cm x 1 cm guide. Assume air filled wave guide with transformer section having same width as that of the input and output sections.
 A Height = 1.414 cm, Length = 3 cm B Height = 1.5 cm, Length = 2.5 cm C Height = 1.414 cm, Length = 2.5 cm D Height = 1.5 cm, Length = 3 cm
Question 96 Explanation:
The Correct Answer Among All the Options is C
height =1.414cm
Length = 2.5cm
Refer the Topic Wise Question for Waveguides Electromagnetics
 Question 97
A cell phone transmits at a power level of 800mW with an antenna gain of 3.0 dB. The cell tower has an antenna gain of 10.0 dB and is at a distance of 5 km away. Transmission frequency is 600 MHz. Noise level at Receiver Input is -95 dBm and required Signal to Noise ratio to close the link is 5dB. Find the link margin in dB. (assume )
 A 150 dB B 60 dB C 30 dB D 35 dB
Question 97 Explanation:
The Correct Answer Among All the Options is C

= transmitted power
=transmitter gain =3dB=10=>
=effective aperture =
R= distance from transmitter
= =10dB = 10 =>
On putting values, we get, =
Given noise(N) in dB=-95dBm =10
ratio in dB :
10 =10log - 10logN
=10 log - (-95)
=35dB
Required ratio in dB = 5dB
= 30dB
Refer the Topic Wise Question for RADAR and Optical Fibers Electromagnetics
 Question 98
What is the value of magnetic flux in Weber, if it is 2000 in Maxwell?
 A 2 x 10-5 B 2 x 10-3 C 2 x 105 D 2 x 103
Question 98 Explanation:
The Correct Answer Among All the Options is A
1 Maxwell =
2000 Maxwell = 2000
= 2
Refer the Topic Wise Question for Electrostatics Electromagnetics
 Question 99
A monostatic pulsed radar operating at 30GHz has a transmitter with 2KW O/P power and an antenna with 30dB gain. Minimum detectable signal in the receiver is -100dBm. Determine the maximum range of the radar, if it is requidred to detect a target having radar cross section of 10sq.m (consider log10 4 = 1.1). Assume EM wave propagate under ideal conditions.
 A 10 km B 21.5 km C 56 km D 100 km
Question 99 Explanation:
The Correct Answer Among All the Options is A
Given data are
F=30GHz =>

30 =>

R =(
On putting all values. We get
R = m=10km
Refer the Topic Wise Question for RADAR and Optical Fibers Electromagnetics
 Question 100
Which of the following statement is not true about delay line cancellers?
 A It eliminates DC components of fixed targets and passes AC components of moving targets B It is used in moving target indicator radar C Time delay in one channel of the delay line canceller is one half of the pulse repetition period D It rejects any moving target whose Doppler frequency happens to be the same as the PRF or a multiple thereof
Question 100 Explanation:
The Correct Answer Among All the Options is C
Delay lines are used in moving target indicator radar. moving target indicator removes the clutter due to stationary targets and ground objects. The basic principle of moving target indicator is to compare a set of received echoes with those received during the previous sweep and cancelling out those whose phase has remain unchanged. Stationary target will give same phase in every cycle unlike moving targey. A single pulse of the received signal at the PRF(pulse repetition frequency) i.e the reciprocal of the time between successive pulses was stored in the delay line. .
Refer the Topic Wise Question for RADAR and Optical Fibers Electromagnetics
 Question 101
An air filled rectangular waveguide with dimensions a = 75 mm, b = 37.5 mm has same guide wavelength at frequencies f1 and f2 when operated at TE10 and TE20 modes respectively. If the frequency f1 is GHz, what is frequency f2 in GHz?
 A 10 B 5 C D
Question 101 Explanation:
The Correct Answer Among All the Options is B
Given , a=75mm
b=37.5mm

As we know, guide wavelength in rectangular waveguide,
Cut-off frequency is given by ,
And Cut-off frequency in case of air-filled waveguide ,
For mode,

For mode,

Now,

=
On solving we get,

Refer the Topic Wise Question for Waveguides Electromagnetics
 Question 102
A waveguide of dimensions a = 15 mm and b = 7.5 mm is used as a high-pass filter. If the stop band attenuation required at 8 GHz is ~109.2 dB, what is the length of the filter? (assume conductor losses to be zero, approximate = 3.14 and 1 Np ~8.69 dB) (log10 e = 0.4343)
 A 100 mm B 869 mm C 86.9 mm D 54.6 mm
Question 102 Explanation:
The Correct Answer Among All the Options is A
a=15mm, b=7.5mm
For
Propagation constant
If , the will become real and it will attenuate.
Therefore,
For m=1, n=0
For dominate mode ,
=10 =40??
So ,
Attenuation at 8GHz= -109.2dB
As we know in a waveguide, if input is then o/p after travelling z distance

20 = -109.2dB
On solving, we get ,
z=100mm
Refer the Topic Wise Question for Waveguides Electromagnetics
 Question 103
An RF signal is applied to a 50 lossless transmission line which is terminated in a load with impedance, ZL = j50. The wavelength is 8 cm. Find the position of voltage and current maximum respectively nearest to the load measured from load end?
 A 1 cm, 3 cm B 3 cm, 1 cm C 3 cm, 5 cm D 5 cm, 3 cm
Question 103 Explanation:
The Correct Answer Among All the Options is A
, it is purely imaginary.
We know,
if load is resistive then waveform of is

if load is purely inductive then waveform of is

, this is equation to find location of maxima.

Reflection coefficient () = =

Therefore,

=1cm (it is voltage maxima)
From the above drawn waveform we have seen that current maxima occurs after distance
= 1+ =1+ = 3cm
Refer the Topic Wise Question for Transmission Lines Electromagnetics
 Question 104
For a conservative vector field F below, which of the following is the scalar Potential?
F = a is an integer
 A Cannot be found B C D
Question 104 Explanation:
The Correct Answer Among All the Options is B
for a conservative /irrotational field
=0
= 0
On solving it for ‘a’, we get
a =1
now, () +() ……………….(1)
as we know , , where V is scalar potential.
…………………(2)
On comparing (1) and (2)

= + f(y, z) {f(y,z) is a constant}
= + f(y, z)
Similarly, =

Therefore V= + +
V=
Refer the Topic Wise Question for Electrostatics Electromagnetics
 Question 105
A cylindrical waveguide with radious of 3.5 cm has waves travelling in TM12 mode. The value of 1st zero of 2nd order Bessel function is 7. Find the cut-off wavelength for this mode.
 A cm B 1.5 cm C 2 cm D /2 cm
Question 105 Explanation:
The Correct Answer Among All the Options is A
for circular waveguide in modes.

n= 1 (first zero);m=2(second order)
Given, , a=3.5cm
Therefore ,
Cut-off wavelength(= =>
Refer the Topic Wise Question for Waveguides Electromagnetics
 Question 106
Relationship between doppler frequency shifts of two radars A and B having 0.1 foot and 0.05 foot wavelengths, approaching the target at 1000 feet per second and 2000 feet per second rate respectively, will be
 A Doppler frequency shift of radar A will be one-fourth of doppler frequency shift of radar B B Doppler frequency shift of radar A will be one-half of doppler frequency shift of radar B C Doppler frequency shift of radar A will be double of doppler frequency shift of radar B D Doppler frequency shifts of radar A and radar B will be same
Question 106 Explanation:
The Correct Answer Among All the Options is A
Velocity of Radar A=1000ft/second, and velocity of radar B=2000ft/second. We have to determine the doppler shift for both the radars to check which one is greater than the other, and by how much.
Now, doppler shift of a radar is generally given by the formula: 2V/λ
Now for radar A=> 2(1000)/0.1λ=> 20,000/λ
And for radar B=> 2(2000)/0.05λ=> 80,000/λ
So, DSB/DSA=> 80,000/λ / 2000/λ
So, clearly we can say that:
Refer the Topic Wise Question for RADAR and Optical Fibers Electromagnetics
 Question 107
The temperature below which certain materials are antiferromagnetic and above which they are paramagnetic is called
 A Weiss temperature B Curie temperature C Neel temperature D None of the above
Question 107 Explanation:
The Correct Answer Among All the Options is C
Neel temperature also called as magnetic ordering temperature is a certain temperature above which antiferro-magnetic materials become paramagnetic. This is the temperature at which the thermal energy of antiferromagnetic material gets to such a point where it becomes large enough to damage the magnetic ordering.
Refer the Topic Wise Question for Electrostatics Electromagnetics
 Question 108
In a specimen of ferromagnetic material with saturation magnetization as 8000 Gauss, as the flux density is increased from 0 to 2.5 T, will
 A Increase B Decrease C First decrease then increase D First increase then decrease
Question 108 Explanation:
The Correct Answer Among All the Options is D
Generally B= µ0 µr(H+M).
Now, from this we can write, µr=(B/ µ0)H
The B-H curve of a ferromagnetic material is shown below:

'H' represents magnetic field strength, and 'B' represents degree of magnetization.
Now, at the origin=> No magnetic field, no magnetization. Now if we apply the magnetic field, then the ferromagnetic material becomes magnetic. The B-H curve generally is an indication of how much µr is changing/varying. So, definitely we can say that answer is option (d)
Refer the Topic Wise Question for Electrostatics Electromagnetics
 Question 109
An electromagnetic wave propagates through a lossless insulator with a velocity 1.5x1010 cm/s. Calculate the electric and magnetic properties of the insulator if its intrinsic impedance is ohms
 A =2.66 =1.5 B =1.5 = 2.66 C =1.2 = 2.0 D =2.0=1.2
Question 109 Explanation:
The Correct Answer Among All the Options is A
Given=> V=1.5 x 1010 cm/s=1.5 x 108 m/sec
Intrinsic impedance (Z0)= 90
We have to determine => ξr and µr
We know that intrinsic impedance is given as:
Z0= 120 =>90=120......................... (a)
And velocity, V= C/
On putting V and C values, we get: µrξr=4.... (b)
From (a) we can write: = 90/120
So=> µr/ξr= 9/16..... (c)
Multiplying (b) and (c) we get: µr=3/2
Again, from (b), putting the value of µr=3/2, we get: ξr=8/3= 2.66, and µr=3/2=1.5
Refer the Topic Wise Question for Waves and Properties Electromagnetics
 Question 110
A square waveguide carries TE11 mode whose axial magnetic field is given by Hz = H0 cos(x/) cos(y/) A/m, where waveguide dimensions are in cm. What is the cut-off frequency of the mode?
 A 5.5 GHz B 6.5 GHz C 7.5 GHz D 8.5 GHz
Question 110 Explanation:
The Correct Answer Among All the Options is C
Given: TE11 mode(Square waveguide)
Axial magnetic field Hz= H0cos(/)cos(y/
We have to determine=> Cut-off frequency of TE11
General form of axial magnetic field is given as:
Hz= H0cos(mx/a)cos(ny/b)
Now, TE11=> m=1, n=1
Comparing with the equation given in question we get: a= and b=
So, cut-off wavelength λc= 2ab/
So, on putting values=> λc=4
So, cut-off frequency fc= C/λ=> 7.5GHz
Refer the Topic Wise Question for Waveguides Electromagnetics
 Question 111
The Eddy current loss is proportional to the
 A Frequency B Square of the frequency C Cube of the frequency D Square root of the frequency
Question 111 Explanation:
The Correct Answer Among All the Options is B
Eddy current loss in a transformer is fixed, and it depends on the core material's magnetic properties. Eddy current loss is given as:
We= PB2max.f2t2watt
So definitely answer is option (b)
Refer the Topic Wise Question for Electrostatics Electromagnetics
 Question 112
From the following Relative amplitude vs Frequency plot, identify the type of noise which the sections A, B, C & D depict.

(i) Thermal Noise (ii) Power line pick up
(iii) Power supply (EPC) switching noise (iv) 1/f noise
 A A-i, B-ii, D-iv B A-ii, B-i, C-iv, D-iii C A-iv, B-ii, C-iii, D-i D B-iv, C-ii, D-i
Question 112 Explanation:
The Correct Answer Among All the Options is C
Here, from the graph we have to determine the type of noise at each region.
First region A=> power is minus, so it is extremely low frequency, which is why it can said as Pink noise or '1/f' noise. The PSD of this noise is inversely proportional to the frequency of the signal.
Next region B=> This is power line pick up noise. Power line noise generally interferes with wireless communication and broadcasting. It can also disrupt television, radio and other important communication systems.
Next region C=> It is the noise that mainly arises in switched mode power supply systems. It is the power supply switching noise.
Last is region D=> It is thermal noise. This noise is also called as Johnson nyquist noise, and it arises due to the thermal distress (charge carriers).
Refer the Topic Wise Question for Waves and Properties Electromagnetics
 Question 113
The electric field of a linearly polarized electromagnetic wave is given by is incident upon a linearly polarized antenna whose electric field polarization is expressed as Find the polarization loss factor.
 A 1/2 B 3/2 C 2/3 D 1/4
Question 113 Explanation:
The Correct Answer Among All the Options is A
Here we have to find out polarization loss factor. Now, Polarization loss is generally given by the formula:
|E(incident). E(transmitted)|2/ |E(incident)|2. |E(transmitted)|2
Now, from the data given in the question, we can put the values in the formula as:
|ax(ax+ay)|2/|ax|2|ax+ay|2
On solving this we get= 1/2
Refer the Topic Wise Question for Waves and Properties Electromagnetics
 Question 114
A lossless T-junction two way power divider has a source impedance, input transmission line impendence and o/p port load impendence of 50. Find the output characterization impedances so that the input power is divided in a 2:1 ratio.
 A z1= 150, z2 = 75 B z1 = 50, z2= 100 C z1= 60, z2= 120 D z1 = 30, z2= 60
Question 114 Explanation:
The Correct Answer Among All the Options is A
The T junction power divider is a network that generally has 3 ports, and is used for power dividing or power combining.
The equivalent electrical circuit is shown below:

Here, Yin= jB+(1/Z1)+(1/Z2)=(1/Zc)
Now, input power(at the matched divider) can be given as: Pin= (1/2)(|V|2/Z1)=Pin/3
So, based on this the other output powers can be calculated as follows:
P1= (1/3)Pin and P2= (2/3)Pin[Since input power is divided in the ratio 2:1]
So, now, Z1 and Z2 can be calculated as:
Z1= 150Ω[Since Z1=3Zc=3(50) is given in the question]
Also, Z2= 75Ω[Since Z2= (3/2)Zc=(3/2)(50)]
Refer the Topic Wise Question for Transmission Lines Electromagnetics
 Question 115
A gain-standard horn is known to have a gain G = 10. It is being used to measure the gain of a large directional antenna by the comparison method. When the antenna being measured is connected to the receiver it is found to be necessary to insert an attenuator adjusted to attenuate by 23 dB in order to have the same receiver output that was observed with the horn connected. What is the gain of the large antenna?
 A 13 dB B 23 dB C 33 dB D 230 dB
Question 115 Explanation:
The Correct Answer Among All the Options is C
Given=> Gain(G) of horn antenna=10
Si, in dB, gain G= 10log10=10dB
Also=> We have a large directional antenna.
Now, gain of large directional antenna - Attenuator=10dB
Let large directional antenna gain = 'X' dB
So, we can write: X-23dB=10dB=>X=33dB
Refer the Topic Wise Question for Waves and Properties Electromagnetics
 Question 116
A paraboloidal-reflector antenna is designed for operation at 3 GHz. Its largest aperture dimension is 20 feet. It is desired to build a scale model of this antenna with the largest aperture dimension scaled to 18 inches. At what frequency must this model be operated in order to have the same pattern as the full-size antenna?
 A 10 GHz B 20 GHz C 40 GHz D 4 GHz
Question 116 Explanation:
The Correct Answer Among All the Options is C
Given=> Frequency(Paraboloid reflector antenna)=3GHz
and D=20 feet
We know that for a paraboloid reflector antenna gain is given as: G= 6(λf)2
Now 18 inches=1.5 feet.
We know that Gain 6(Df)2
From this we can say that Gain (Df)2
So=> (D1f1)2= (D2f2)2[D2f2=> parameter of scale model of original antenna]
D2=20feet and D1=18 inch=1.5 feet
Therefore=> (20 x 3)2= (1.5 x f2)2
On solving we get: f2=40GHz
Refer the Topic Wise Question for Waves and Properties Electromagnetics
 Question 117
An antenna has a radiation resistance of 72 , a loss resistance of 8 Ω and power gain of 16. Calculate its directivity.
 A 15.8 B 16.8 C 17.8 D .18.7
Question 117 Explanation:
The Correct Answer Among All the Options is C
Given=> Rr=72Ω, RLoss=8Ω and Pgain=16
We have to determine=> Directivity
Now, gain of antenna=Directivity x (ո)
So, D= Gain/ո => 17.8
Refer the Topic Wise Question for Waves and Properties Electromagnetics
 Question 118
The current density at the surface of a thick metal plate is 100 A/m2. What is the skin depth if the current density at a depth of 0.0059 cm is 0.272 A/m2?
 A 5m B 10 m C 15m D 20m
Question 118 Explanation:
The Correct Answer Among All the Options is B
Given=> Current density=> 100A/m2
We have to find=> Skin depth(δ)
Now, δ= (1/σ)
Current density reduces in metal(from surface) at the rate equal to=>
So, we can write: 100=0.27
Taking Log on both sides:
- .0059 x 10-2 / δ = ln[0.272/1000]
On solving this we will get δ=10 µm
Refer the Topic Wise Question for Electrostatics Electromagnetics
There are 118 questions to complete.