27 + Interview Questions in Advanced And Tricky Questions in Electromagnetic Theory Page 1 InterviewSolution

1.	In a microwave test bench, why is the microwave signal amplitude modulated at 1 kHz?(a) To increase the sensitivity of measurement(b) To transmit the signal to a far off place(c) To study amplitude modulation(d) Because crystal detector fails at microwave frequenciesI had been asked this question in an internship interview.The doubt is from Advanced and Tricky Questions in chapter Advanced and Tricky Questions of Electromagnetic Theory
Answer» RIGHT ANSWER is (d) Because crystal detector fails at microwave frequencies Explanation: SINCE crystal detector fails at microwave frequencies, microwave signal AMPLITUDE is modulated at 1kHz.

Discussion

2.	The modes in a rectangular waveguide are denoted by TEmn / TMmn, where m and n are the Eigen values along the larger and smaller dimensions of the waveguide respectively. Which one of the following statements is true?(a) The TM10 mode does not exist(b) The TE10 mode does not exist(c) The TE10 and TM10 both exist and have same cut off frequencies(d) When m and n are increases, the cut off frequency decreasesThis question was posed to me during an online interview.This interesting question is from Advanced and Tricky Questions in chapter Advanced and Tricky Questions of Electromagnetic Theory
Answer» Right choice is (a) The TM10 mode does not exist Easiest EXPLANATION: For TM mode, TM00, TM10, TM01 does not exist. For TE mode, TE00 does not exist but TE10 and TE01 exists.

Discussion

3.	A transmission line of pure resistance characteristic impedance is terminated with an unknown load. The measured value of VSWR on the line is 2 and a voltage minimum point is found to be at the load. The load impedance is then(a) Complex(b) Purely capacitive(c) Purely resistive(d) Purely inductiveI got this question during an interview.Question is from Advanced and Tricky Questions topic in chapter Advanced and Tricky Questions of Electromagnetic Theory
Answer» Right CHOICE is (c) PURELY resistive The best I can explain: Given, voltage MINIMUM point is at load. If minimum voltage or maximum voltage occurs at the load for a lossless transmission line then the load IMPEDANCE is purely resistive.

Discussion

4.	Which one of the following field patterns represents a TEM wave travelling in the positive x direction?(a) E = +8y, H = -4z(b) E = -2y, H = -3z(c) E = +2z, H = +2y(d) E = -3y, H = +4zThe question was posed to me in homework.The question is from Advanced and Tricky Questions in portion Advanced and Tricky Questions of Electromagnetic Theory
Answer» CORRECT choice is (b) E = -2Y, H = -3z The EXPLANATION: To get wave travelling in the positive direction, the E component has to be in negative y direction and the H component has to be in negative Z direction. Thus E = -2y and H = -3z is the RIGHT option.

Discussion

5.	A two wire transmission line of characteristic impedance Z is connected to a load impedance ZL(ZL and Zo are not equal). Impedance matching cannot be achieved with(a) A quarter wavelength transformer(b) A half wavelength transformer(c) An open circuited parallel stub(d) A short circuited parallel stubThe question was posed to me in final exam.Origin of the question is Advanced and Tricky Questions topic in division Advanced and Tricky Questions of Electromagnetic Theory
Answer» Right OPTION is (b) A HALF wavelength transformer For EXPLANATION: When the characteristic and load IMPEDANCE are not same, a half wavelength transformer cannot be used for impedance MATCHING because when l = wavelength/2, we get Zin = ZL.

Discussion

6.	A transmission line whose characteristic impedance is a pure resistance(a) Must be a lossless line(b) Must be a distortionless line(c) May not be a lossless line(d) May be a lossless and may not be a distortionless lineI have been asked this question by my school teacher while I was bunking the class.My question comes from Advanced and Tricky Questions topic in portion Advanced and Tricky Questions of Electromagnetic Theory
Answer» The correct option is (d) MAY be a lossless and may not be a DISTORTIONLESS line Easy EXPLANATION: When the characteristic line is a pure resistance, the line must be a distortionless line. But it may not be a lossless line.

Discussion

7.	Consider a transmission line of characteristic impedance 50 ohm. Let it be terminated at one end by +j50 ohm. The VSWR produced by it in the transmission line will be(a) 1(b) 0(c) Infinity(d) +jI had been asked this question during an interview for a job.Query is from Advanced and Tricky Questions in portion Advanced and Tricky Questions of Electromagnetic Theory
Answer» The CORRECT OPTION is (c) Infinity Explanation: The reflection coefficient is given by R = j50 – 50/j50 + 50 = j – 1/j + 1. Thus the reflection coefficient is given by 1. The VSWR = 1 + R/1 – R = 2/0 = infinity.

Discussion

8.	Which parameters cannot be computed from the Smith chart?(a) Impedance(b) Admittance(c) Reflection coefficient and VSWR(d) Intrinsic impedanceThe question was posed to me in an interview.The doubt is from Advanced and Tricky Questions topic in chapter Advanced and Tricky Questions of Electromagnetic Theory
Answer» Right OPTION is (d) Intrinsic impedance The BEST I can explain: From the Smith CHART, the parameters impedance, admittance, reflection coefficient and VSWR can be COMPUTED directly. The intrinsic impedance cannot be calculated.

Discussion

9.	In the design of a single mode step index optical fiber close to upper cut off, the single mode operation is NOT preserved if(a) Radius as well as operating wavelength are halved(b) Radius as well as operating wavelength are doubled(c) Radius is halved and operating wavelength is doubled(d) Radius is doubled and operating wavelength is halvedThe question was asked during an interview.Query is from Advanced and Tricky Questions topic in portion Advanced and Tricky Questions of Electromagnetic Theory
Answer» The correct option is (d) Radius is doubled and operating WAVELENGTH is halved Explanation: The cut off frequency is given by f = 2πa sin α/wavelength, where a is the radius of CORE. For a single mode STEP index fiber, f must lie between 0 and 2.405. THUS to get f below 2.405, the radius must be doubled and wavelength must be halved.

Discussion

10.	The minimum distance of the stub from the load side is 5 cm. Calculate the guided wavelength of the transmission line.(a) 5 cm(b) 2.5 cm(c) 10 cm(d) 1.25 cmThe question was posed to me in final exam.I want to ask this question from Advanced and Tricky Questions topic in portion Advanced and Tricky Questions of Electromagnetic Theory
Answer» RIGHT option is (c) 10 cm Easy explanation: The MINIMUM DISTANCE of the stub from the load line is given by VMIN = wavelength/2. On substituting the given value, we get the GUIDED wavelength as 10 cm.

Discussion

11.	The capacitance per unit length and the characteristic impedance of a lossless transmission line are C and Z respectively. The velocity of a travelling wave on the transmission line is(a) ZC(b) 1/ZC(c) Z/C(d) C/ZThe question was asked during an online interview.This key question is from Advanced and Tricky Questions in portion Advanced and Tricky Questions of Electromagnetic Theory
Answer» Right CHOICE is (b) 1/ZC Easy explanation: The characteristic impedance of the Z = √(L/C) and the VELOCITY of propagation is V = 1/√(LC). THUS we get V = 1/ZC.

Discussion

12.	A lossless line having 50 ohm characteristic impedance and length wavelength/4 is short circuited at one end connected to an ideal voltage source of 1V at the other end. The current drawn from the voltage sources is(a) 0(b) 0.02(c) Infinity(d) 50This question was addressed to me in an interview.This question is from Advanced and Tricky Questions in chapter Advanced and Tricky Questions of Electromagnetic Theory
Answer» The CORRECT option is (a) 0 The BEST I can explain: For a quarter WAVE transformer, the input IMPEDANCE is given by Zin = Z0^2/ZL. The load impedance will be zero in case of short circuit. Thus the input impedance will be infinite. The current drawn is I = V/ZL = 1/∞ = 0.

Discussion

13.	A transmission line is distortionless if(a) RL = 1/GC(b) RL = GC(c) LG = RC(d) RG = LCThe question was posed to me in an international level competition.I'm obligated to ask this question of Advanced and Tricky Questions in portion Advanced and Tricky Questions of Electromagnetic Theory
Answer» CORRECT option is (C) LG = RC Easiest EXPLANATION: Condition for distortionless line is R/L = G/C. In other WORDS, the rise time constant is equal to the fall time constant. HENCE RC = LG.

Discussion

14.	For maximum power transfer, a lossless transmission line 50 ohm is to be matched to a resistive load impedance of 100 ohm. The characteristic impedance of the wavelength/4 transformer is(a) 70.7(b) 50(c) 100(d) InfinityI got this question in quiz.Question is from Advanced and Tricky Questions in section Advanced and Tricky Questions of Electromagnetic Theory
Answer» Right ANSWER is (a) 70.7 The best EXPLANATION: For MAXIMUM power transfer, Zin = Z0^2/ZL. On substituting for the GIVEN values, we get the CHARACTERISTIC impedance as 70.7 ohm.

Discussion

15.	In an impedance Smith chart , a clockwise movement along a constant resistance circle gives rise to(a) Decrease in reactance(b) Increase in reactance(c) No change in reactance(d) No change in impedanceI got this question by my school principal while I was bunking the class.Enquiry is from Advanced and Tricky Questions topic in division Advanced and Tricky Questions of Electromagnetic Theory
Answer» Correct option is (B) Increase in REACTANCE Easiest EXPLANATION: In clockwise DIRECTION, along the constant resistance CIRCLE gives rise to an increase in the value of reactance.

Discussion

16.	For an electromagnetic wave incident from one medium to a second medium, total internal reflection takes place when(a) Angle of incidence is equal to the Brewster angle with E field perpendicular to the plane of incidence(b) Angle of incidence is equal to the Brewster angle with E field parallel to the plane of incidence(c) Angle of incidence is equal to the critical angle with the wave moving from the denser to rarer medium(d) Angle of incidence is equal to the critical angle with the wave moving from the rarer to denser mediumThe question was asked in examination.This is a very interesting question from Advanced and Tricky Questions topic in division Advanced and Tricky Questions of Electromagnetic Theory
Answer» The correct option is (c) Angle of INCIDENCE is equal to the CRITICAL angle with the wave moving from the denser to rarer medium For explanation I would say: Total INTERNAL reflection takes PLACE when the angle of incidence is greater than the critical angle. Also the wave should MOVE from the denser medium to a rarer medium.

Discussion

17.	In a good conductor the phase relation between the tangential components of electric E and the magnetic field H is as follows(a) E and H are in phase(b) E and H are out of phase(c) H leads E by 90(d) E leads H by 45The question was posed to me in an international level competition.My question is based upon Advanced and Tricky Questions topic in division Advanced and Tricky Questions of Electromagnetic Theory
Answer» Right ANSWER is (d) E leads H by 45 Easiest explanation: In a conductor, the intrinsic impedance gives the PHASE relation between E and H. For a conductor, the electric field and magnetic field are in 45 DEGREE phase difference. E and H are 45 leading.

Discussion

18.	The intrinsic impedance of copper at high frequencies is(a) Purely resistive(b) Purely inductive(c) Complex with a capacitive component(d) Complex with a inductive componentThis question was posed to me in final exam.I'd like to ask this question from Advanced and Tricky Questions topic in chapter Advanced and Tricky Questions of Electromagnetic Theory
Answer» Correct choice is (d) COMPLEX with a inductive component The best explanation: The intrinsic IMPEDANCE is given by √(jwµ√ϭ + jw€). Since COPPER is a good conductor, ϭ << jw€, thus the intrinsic impedance will have +J component only. This refers to complex with an inductive component.

Discussion

19.	Copper behaves as a(a) Conductor always(b) Conductor or dielectric depending on the applied electric field strength(c) Conductor or dielectric depending on the frequency(d) Conductor or dielectric depending on the electric current densityThis question was posed to me during an online exam.My question comes from Advanced and Tricky Questions topic in portion Advanced and Tricky Questions of Electromagnetic Theory
Answer» The correct option is (a) CONDUCTOR always The EXPLANATION: The LOSS tangent for copper is very large due to its high conductivity. This SHOWS that the copper BEHAVES as a conductor in all conditions.

Discussion

20.	Identify which one of the following will NOT satisfy the wave equation.(a) 50e^j(wt – 3z)(b) sin(w(10z + 5t))(c) cos(y^2 + 5t)(d) sin x cos tThis question was addressed to me during an interview.Origin of the question is Advanced and Tricky Questions in division Advanced and Tricky Questions of Electromagnetic Theory
Answer» The correct answer is (C) cos(y^2 + 5T) Explanation: The WAVE cos(y^2 + 5t) does not SATISFY the general wave equation. Thus it is not an electromagnetic wave.

Discussion

21.	The electric field of a uniform plane electromagnetic wve in free space, along the positive direction, is given by E = 10(ay + jaz)e^-j25x. The frequency and polarization of the wave, respectively are(a) 1.2 GHz, left circular(b) 4 GHz, left circular(c) 1.2 GHz, right circular(d) 4 GHz, right circularThis question was posed to me in an interview for internship.My query is from Advanced and Tricky Questions in section Advanced and Tricky Questions of Electromagnetic Theory
Answer» The CORRECT choice is (a) 1.2 GHZ, left circular The best explanation: The amplitudes of the components are the same. Hence it is circular polarization. The phase difference is +90 degree. Thus it is left HAND circular polarisation. The frequency f = c/wavelength = 3 X 10^8 x 25/2 x 3.14 = 1.2 GHz.

Discussion

22.	The electric field strength at a far-off point P due to a point charge, +q located at the origin O is 100 milliVolt/meter. The point charge is now enclosed by a perfectly conducting hollow metal sphere with its centre and the origin O. The electric field strength at the point, P is(a) Remains unchanged in its magnitude and direction(b) Remains unchanged in its magnitude but reverse in direction(c) Would be that due to a dipole formed by the charge, +q, at O and -q induced(d) Would be zeroThis question was addressed to me in an interview for internship.Asked question is from Advanced and Tricky Questions topic in section Advanced and Tricky Questions of Electromagnetic Theory
Answer» CORRECT choice is (d) WOULD be zero The best explanation: ACCORDING to Gauss Law, the total displacement or electric flux through any CLOSED surface surrounding charges is equal to the amount of charge enclosed. The total enclosed charge is -q + q = 0. Thus the flux and electric field strength will be zero.

Discussion

23.	An electric field on a plane is described by its potential V = 20(r^-1 + r^-2), where r is the distance from the source. The field is due to(a) A monopole(b) A dipole(c) Both a monopole and a dipole(d) A quadrupleI got this question in an interview.My enquiry is from Advanced and Tricky Questions topic in section Advanced and Tricky Questions of Electromagnetic Theory
Answer» The CORRECT ANSWER is (c) Both a monopole and a dipole To explain I WOULD say: In the potential given, ONE component is inversely proportional to r, which is due to a monopole and the other component is inversely proportional to r^2, which is due to a dipole.

Discussion

24.	For the wave equation E = 10sin (wt-5z)ax, the wave propagation will be in the direction of(a) Y direction(b) Z direction(c) X direction(d) XY directionThis question was posed to me during an interview for a job.I want to ask this question from Advanced and Tricky Questions in chapter Advanced and Tricky Questions of Electromagnetic Theory
Answer» Correct option is (b) Z direction The best I can EXPLAIN: The EQUATION represents the electric FIELD COMPONENT of the wave. Here, AX represents the electric wave direction and z represents the wave direction.

Discussion

25.	Magnetic vector potential is a vector(a) Whose curl is equal to the magnetic flux density(b) Whose curl is equal to the electric field intensity(c) Whose divergence is equal to electric potential(d) Which is equal to the vector product E x HI had been asked this question in an international level competition.Query is from Advanced and Tricky Questions in portion Advanced and Tricky Questions of Electromagnetic Theory
Answer» RIGHT choice is (a) Whose curl is EQUAL to the MAGNETIC flux density The explanation: The magnetic vector POTENTIAL is A. The curl of A is a vector and it is equal to the magnetic flux density. It is given by Curl(A) = B.

Discussion

26.	The depth of penetration of a wave in a lossy dielectric increases with increasing(a) Conductivity(b) Permeability(c) Wavelength(d) PermittivityI have been asked this question in an internship interview.Query is from Advanced and Tricky Questions in chapter Advanced and Tricky Questions of Electromagnetic Theory
Answer» CORRECT choice is (c) WAVELENGTH Easy explanation: The DEPTH of penetration or skin depth is inversely proportional to the frequency. THUS it has to be DIRECTLY proportional to the wavelength.

Discussion

27.	The tangential component of an electric field will be continuous in which boundary?(a) Conductor-Conductor(b) Conductor-Dielectric(c) Dielectric-Dielectric(d) Any boundaryThis question was addressed to me during an interview.My query is from Advanced and Tricky Questions in portion Advanced and Tricky Questions of Electromagnetic Theory
Answer» Correct answer is (d) Any BOUNDARY The BEST I can EXPLAIN: The TANGENTIAL COMPONENT of an electric field will be continuous in any type of boundary.

Discussion

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A transmission line is distortionless if(a) RL = 1/GC(b) RL = GC(c) LG = RC(d) RG = LCThe question was posed to me in an international level competition.I'm obligated to ask this question of Advanced and Tricky Questions in portion Advanced and Tricky Questions of Electromagnetic Theory