112 + Interview Questions in Electromagnetic Field Theory in Electronics and Communication Engineering Page 2 InterviewSolution

51.	The numerical value of directivity of current element of half-wave dipole is 1.76 and 2.15 dB respectively. The directive gain of half-wave dipole over current element will be
Answer» 2.15 - 1.76 = 0.39 db.

Discussion

52.	The maximum effective aperture of an antenna which is operating at wavelength of 2 m and has directivity of 100 is
Answer»

Discussion

53.	A 10 GHz signal propagates in a waveguide with a phase velocity of 4 x 10 m/s. If the signal produces standing wave in the guide, then the distance between successive minimal will be
Answer» f = 10 GHz, v = 4 x 108 m/sec, .

Discussion

54.	The incidence from dielectric medium 1 (ε) into dielectric medium 2 (ε), Brewster angle θ and the corresponding angle of transmission θ for will be respectively
Answer» Brewster angle θ = tan-1

Discussion

55.	A medium of relative permittivity ε = 2 forms an interface with free space. A point source of EM energy is located in the medium at a depth of 1 meter from the interface. Due to the total internal reflection, the transmitted beam has a circular cross-section over the interface. The area of the beam cross section at the interface is given by
Answer»

Discussion

56.	A transmission line of characteristic impedance = 50 &ohm;. Phase Velocity = 2 x 10 m/sec, and length = 1 m is terminated by a load = (30 - 40) ohms. The input impedance of the line for a frequency of 100 MHz will be
Answer» .

Discussion

57.	A circular waveguide carries TE mode whose radial electric-field is given by E = E J () sin φ V/m where '' is the radial distance in cm, from the waveguide axis. The cut-off wavelength of the mode is
Answer» .

Discussion

58.	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
Answer» .

Discussion

59.	A rectangular waveguide having TE mode as dominant mode is having a cut off frequency of 18 GHz for the TE mode. The inner broad wall dimension of the rectangular waveguide is
Answer»

Discussion

60.	A 50 characteristic impedance line is connected to a load which shows a reflection coefficients of 0.268. If V = 15 volt, then the net power delivered to the load will be
Answer» r , P = v2/ZL.

Discussion

61.	If wave of critical frequency 30 MHz is departing at an angle of 60°, then the MUF is given to be
Answer» MUF = fc sec θ

Discussion

62.	An antenna having an effective temperature of 27°K is fed into a microwave amplifier that has an effective noise temperature of 30 K. Calculate the available noise power per unit bandwidth
Answer» where K is Boltzmann constant.

Discussion

63.	Two identical and parallel dipole antenna are kept apart by a distance of λ/4 in the H-plane. They are fed with equal currents but the right most antenna has a phase shift of + 90°. The radiation pattern is given as
Answer» There will be no pattern in E-plane, only in H-Plane.

Discussion

64.	Cassergain feed is used with a parabolic reflector to
Answer» Cassergain is a type of feed, which is used to allow parabolic reflector to provide feed at a convenient point.

Discussion

65.	Voltage standing wave pattern in a loss less transmission line with characteristic impedance 50 &ohm; and a resistive load is shown in the figure. The value of load resistance is
Answer» Vmax = 4, Vmin = 1,

Discussion

66.	The effective electrical length of an antenna is __________ its physical length
Answer» Physical length is geometrical length, Effective length is increased by method called loading.

Discussion

67.	∇ . = 0 is frequently known as
Answer» Equation of continuity ∇ x J = 0.

Discussion

68.	The magnetic field intensity vector of a plane wave is given by (, , , ) = 10 sin (5000 + 0.004 + 30 ), where denotes unit vector in direction the wave is propagating with a phase velocity.
Answer» (x, y, z, t) = 10 sin (5000t + 0.004x + 30) Wave is propagating in - ve direction, hence v = - 1.25 x 107 m/sec.

Discussion

69.	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?
Answer» Preflected = \|δ\|2 Pincident \|δ\|2 = 0.25 .

Discussion

70.	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
Answer» = 101 Pr = 10 watt.

Discussion

71.	A parallel polarized wave is incident from air into paraffin having relative permittivity 3, the value of its Brewster angle is
Answer» Brewster angle θ = tan-1 .

Discussion

72.	The radiation resistance of a λ/16 wire dipole in free space will be nearly
Answer» Rr = 80p2.

Discussion

73.	Two identical antennas are placed in the θ = /2 plane as shown in the figure. The elements have equal amplitude excitation with 180° polarity difference, operating of the far-zone resultant electric field strength normalized with that of a single element, both computed for φ = 0, is
Answer» Normalised array factor = n cos where φ is the phase difference. φ = (βd sin θ cos φ + θ1) and θ = 90°, φ = 45°

Discussion

74.	Find the noise factor for an antenna at 27°C with equivalent noise temperature 30°K
Answer» Te = T0(F - 1) .

Discussion

75.	The displacement flux density at a point on the surface of a perfect conductor is = 2( - )c/m pointing away from the surface. The charge density at that point c/m will be
Answer» ∇ . D = r.

Discussion

76.	Characteristic impedance of a transmission line is 50 &ohm;. Input impedance of the open circuited line. Z = 100 + J150 &ohm;. When transmission line is short circuited, then value of the input impedance will be
Answer» ZC = ZOC - ZSC 50 = (100 + j150)(ZSC) .

Discussion

77.	The input impedance of short-circuited line of length where λ/4 < < λ/2, is
Answer» l < λ/4, ZL = 0 , if Zd comes +j kZC then inductive, If Zd comes -j kZC then capacitive. for 0 ≤ l ≤ 1/4, λ ≤ l ≤ 3λ/4 will be inductive.

Discussion

78.	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.
Answer» .

Discussion

79.	Find the radiation resistance of an antenna of length λ/10 meter?
Answer» .

Discussion

80.	Charge needed within a unit sphere centred at the origin for producing a potential field,
Answer» q = 120p coulomb, r = 1 meter.

Discussion

81.	In a 100 turn coil, if the flux through each turn is ( - 2)W, the magnitude of the induced emf in the coil at a time of 4 sec is
Answer» E = 100 (3t2 - 2) 100(46) 4600 mV 4.6 V.

Discussion

82.	The torque (in mm) acting on a circular current loop of radius 1 mm in the plane, connected at the origin and with current 0.1 A, flowing in the sense of increasing in a magnetic field is
Answer» t = M x B

Discussion

83.	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.
Answer» Wave impedance .

Discussion

84.	Calculate wave impedance for TE mode
Answer» .

Discussion

85.	Calculate the wave impedance for TM mode in rectangular waveguide for dominant mode at 3 GHz having
Answer» η = 226 &ohm;.

Discussion

86.	The divergence of the electric field intensity at any point equals
Answer»

Discussion

87.	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
Answer» γ = a + jβ, a = 0 β = ωLC.

Discussion

88.	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
Answer» Skin depth δ2 = δ1/2 .

Discussion

89.	What is the characteristic impedance at 10 MHz?
Answer» , not depend upon frequency.

Discussion

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
Answer» 6 dB = 10 log10 = 100.6 3.98 Pr = 3.98 mW.

Discussion

91.	A uniform plane wave is one in which
Answer» For uniform plane wave, E and H must be in a plane but perpendicular to each other.

Discussion

92.	The electric field of the incident wave is , where ω = 3 x 10 and β = 10 . The electric field of the transmitted wave E is given by
Answer» In, question, it is not mentioned, about medium; dielectric etc. Ei = Et + Er Et = Er Et = Ei.

Discussion

93.	A short circuited stub is shunt connected to a transmission line as shown in the figure is, if = 500 ohms, the admittance seen at the function of the stub and the transmission line is
Answer»

Discussion

94.	A wave is propagated in a waveguide at frequency of 9 GHz and separation is 2 cm between walls Calculate group velocity for dominant mode.
Answer» Vg . Vp = C2 where .

Discussion

95.	Consider a 300 &ohm;, quarter wave long at 1 GHz transmission line as shown in figure. It is connected to a 10 V, 50 &ohm; source at one end is left open circuited at the other end. The magnitude of the voltage at the open circuit end of the line is
Answer» γ = a + jβ a = 0 γ = jβ Propagating wave v = VI e-rz + VR erz No change in the voltage at the open end it will same, vr = 10 volt.

Discussion

96.	The phase angle corresponding to λ/4 in a standing-wave pattern is
Answer»

Discussion

97.	A hollow rectangular waveguide has dimensions = 2. Calculate the amount of attenuation, if the frequency is 3 GHz, and = 1 cm.
Answer» Since, wave is attenuated hence β = 0 and Take, dominant mode m = 1, n = 0 .

Discussion

98.	A (75 - 40) W load is connected to a co-axial line of = 75ω at 6 MHz. The load matching on the line can be accomplished by connecting
Answer» ZL = 75 - J . 40, ZC = 75 W, f = 6 mHz Given ZL is capacitive, so proper matching, load must be inductive.

Discussion

99.	A plane wave is characterized by the wave is
Answer» Because, magnitude is different (0.5, 1) and phase is 90°

Discussion

100.	The electric field on the surface of a perfect conductor is 2V/m. The conductor is immersed in water with ε = 80 ε. The surface charge density on the conductor is ((ε = 10/36)F/m)
Answer» .

Discussion

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The numerical value of directivity of current element of half-wave dipole is 1.76 and 2.15 dB respectively. The directive gain of half-wave dipole over current element will be

The maximum effective aperture of an antenna which is operating at wavelength of 2 m and has directivity of 100 is

A 10 GHz signal propagates in a waveguide with a phase velocity of 4 x 10 m/s. If the signal produces standing wave in the guide, then the distance between successive minimal will be

The incidence from dielectric medium 1 (ε) into dielectric medium 2 (ε), Brewster angle θ and the corresponding angle of transmission θ for will be respectively

A transmission line of characteristic impedance = 50 &ohm;. Phase Velocity = 2 x 10 m/sec, and length = 1 m is terminated by a load = (30 - 40) ohms. The input impedance of the line for a frequency of 100 MHz will be

A circular waveguide carries TE mode whose radial electric-field is given by E = E J () sin φ V/m where '' is the radial distance in cm, from the waveguide axis. The cut-off wavelength of the mode is

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 rectangular waveguide having TE mode as dominant mode is having a cut off frequency of 18 GHz for the TE mode. The inner broad wall dimension of the rectangular waveguide is

A 50 characteristic impedance line is connected to a load which shows a reflection coefficients of 0.268. If V = 15 volt, then the net power delivered to the load will be

If wave of critical frequency 30 MHz is departing at an angle of 60°, then the MUF is given to be

An antenna having an effective temperature of 27°K is fed into a microwave amplifier that has an effective noise temperature of 30 K. Calculate the available noise power per unit bandwidth

Two identical and parallel dipole antenna are kept apart by a distance of λ/4 in the H-plane. They are fed with equal currents but the right most antenna has a phase shift of + 90°. The radiation pattern is given as

Cassergain feed is used with a parabolic reflector to

Voltage standing wave pattern in a loss less transmission line with characteristic impedance 50 &ohm; and a resistive load is shown in the figure. The value of load resistance is

The effective electrical length of an antenna is __________ its physical length

∇ . = 0 is frequently known as

The magnetic field intensity vector of a plane wave is given by (, , , ) = 10 sin (5000 + 0.004 + 30 ), where denotes unit vector in direction the wave is propagating with a phase velocity.

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 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 parallel polarized wave is incident from air into paraffin having relative permittivity 3, the value of its Brewster angle is

The radiation resistance of a λ/16 wire dipole in free space will be nearly

Two identical antennas are placed in the θ = /2 plane as shown in the figure. The elements have equal amplitude excitation with 180° polarity difference, operating of the far-zone resultant electric field strength normalized with that of a single element, both computed for φ = 0, is

Find the noise factor for an antenna at 27°C with equivalent noise temperature 30°K

The displacement flux density at a point on the surface of a perfect conductor is = 2( - )c/m pointing away from the surface. The charge density at that point c/m will be

Characteristic impedance of a transmission line is 50 &ohm;. Input impedance of the open circuited line. Z = 100 + J150 &ohm;. When transmission line is short circuited, then value of the input impedance will be

The input impedance of short-circuited line of length where λ/4 < < λ/2, is

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.

Find the radiation resistance of an antenna of length λ/10 meter?

Charge needed within a unit sphere centred at the origin for producing a potential field,

In a 100 turn coil, if the flux through each turn is ( - 2)W, the magnitude of the induced emf in the coil at a time of 4 sec is

The torque (in mm) acting on a circular current loop of radius 1 mm in the plane, connected at the origin and with current 0.1 A, flowing in the sense of increasing in a magnetic field is

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.

Calculate wave impedance for TE mode

Calculate the wave impedance for TM mode in rectangular waveguide for dominant mode at 3 GHz having

The divergence of the electric field intensity at any point equals

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

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

What is the characteristic impedance at 10 MHz?

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 uniform plane wave is one in which

The electric field of the incident wave is , where ω = 3 x 10 and β = 10 . The electric field of the transmitted wave E is given by

A short circuited stub is shunt connected to a transmission line as shown in the figure is, if = 500 ohms, the admittance seen at the function of the stub and the transmission line is

A wave is propagated in a waveguide at frequency of 9 GHz and separation is 2 cm between walls Calculate group velocity for dominant mode.

Consider a 300 &ohm;, quarter wave long at 1 GHz transmission line as shown in figure. It is connected to a 10 V, 50 &ohm; source at one end is left open circuited at the other end. The magnitude of the voltage at the open circuit end of the line is

The phase angle corresponding to λ/4 in a standing-wave pattern is

A hollow rectangular waveguide has dimensions = 2. Calculate the amount of attenuation, if the frequency is 3 GHz, and = 1 cm.

A (75 - 40) W load is connected to a co-axial line of = 75ω at 6 MHz. The load matching on the line can be accomplished by connecting

A plane wave is characterized by the wave is

The electric field on the surface of a perfect conductor is 2V/m. The conductor is immersed in water with ε = 80 ε. The surface charge density on the conductor is ((ε = 10/36)F/m)