Tricky Electromagnetic Theory Questions and Answers

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This set consists of Tricky Electromagnetic Theory Questions and Answers.

1. The tangential component of an electric field will be continuous in which boundary?
a) Conductor-Conductor
b) Conductor-Dielectric
c) Dielectric-Dielectric
d) Any boundary
View Answer

Answer: d
Explanation: The tangential component of an electric field will be continuous in any type of boundary.
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2. The depth of penetration of a wave in a lossy dielectric increases with increasing
a) Conductivity
b) Permeability
c) Wavelength
d) Permittivity
View Answer

Answer: c
Explanation: The depth of penetration or skin depth is inversely proportional to the frequency. Thus it has to be directly proportional to the wavelength.

3. 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 H
View Answer

Answer: a
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.
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4. 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 direction
View Answer

Answer: b
Explanation: The equation represents the electric field component of the wave. Here, ax represents the electric wave direction and z represents the wave direction.

5. 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 quadruple
View Answer

Answer: c
Explanation: 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 r2, which is due to a dipole.
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6. 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 zero
View Answer

Answer: d
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.

7. 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 circular
View Answer

Answer: a
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 108 x 25/2 x 3.14 = 1.2 GHz.
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8. Identify which one of the following will NOT satisfy the wave equation.
a) 50ej(wt – 3z)
b) sin(w(10z + 5t))
c) cos(y2 + 5t)
d) sin x cos t
View Answer

Answer: c
Explanation: The wave cos(y2 + 5t) does not satisfy the general wave equation. Thus it is not an electromagnetic wave.

9. 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 component
View Answer

Answer: d
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.
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10. A loop is rotating about the y axis in a magnetic field B = Bocos(wt + α)at. The voltage in the loop is
a) Zero
b) Due to rotation only
c) Due to transformer action only
d) Due to both rotation and transformer action
View Answer

Answer: d
Explanation: The voltage in the loop is due to two reactions – time varying magnetic field and voltage induced in a loop moving with velocity v in steady magnetic field. Thus the voltage in the loop is due to both rotation and transformer action.

Sanfoundry Global Education & Learning Series – Electromagnetic Theory.
To practice all areas of Electromagnetic Theory, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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