Electromagnetic Theory Questions and Answers – Plane Waves in Free Space

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This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Plane Waves in Free Space”.

1. In free space, the charge carriers will be
a) 0
b) 1
c) 100
d) Infinity
View Answer

Answer: a
Explanation: Free space is not a conductor. Thus the charge carrier in free space is assumed to be zero. But the free space consists of particles or ions that get ionized during conduction.
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2. In free space, which parameter will be unity?
a) Permittivity
b) Absolute permittivity
c) Relative permittivity
d) Permeability
View Answer

Answer: c
Explanation: The relative permittivity is a constant for a particular material. It is unity for free space or air. The absolute permittivity is a constant given by 8.854 x 10-12 C/m2.

3. Which parameter is unity in air medium?
a) Permittivity
b) Absolute permeability
c) Relative permeability
d) Permeability
View Answer

Answer: c
Explanation: In free space or air medium, the relative permeability is also unity, like relative permittivity. The absolute permeability is given by 4π x 10-7 units.
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4. The conductivity in free space medium is
a) Infinity
b) Unity
c) Zero
d) Negative
View Answer

Answer: c
Explanation: As the charge carriers are not available in free space, the conductivity will be very low. For ideal cases, the conductivity can be taken as zero.

5. Zero permeability/permittivity implies which state?
a) No ions are allowed in the medium
b) No current is generated in the medium
c) No magnetic or electric energy is permitted in the medium
d) No resistivity
View Answer

Answer: c
Explanation: The zero permittivity in an electric field refers to the ability of the field/medium to permit electric charges in it. Similarly, zero permeability in a magnetic field refers to the ability of the field/medium to permit the magnetic energy into the field.
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6. The intrinsic impedance of free space is
a) 489
b) 265
c) 192
d) 377
View Answer

Answer: d
Explanation: The intrinsic impedance is the square root of ratio of the permeability to the permittivity. In free space, the permeability and the permittivity is same as the absolute permeability and permittivity respectively. This is due to unity permeability and permittivity in free space. Thus η = √(μ/ε), where absolute permeability is given by 4π x 10-7 and absolute permittivity is given by 8.854 x 10-12. The intrinsic impedance will be 377 ohms.

7. In free space, the condition that holds good is
a) Minimum attenuation and propagation
b) Minimum attenuation and maximum propagation
c) Maximum attenuation and minimum propagation
d) Maximum attenuation and propagation
View Answer

Answer: b
Explanation: The free space does not have any barrier for attenuation. Thus it enables minimum attenuation and maximum propagation. This technique is employed in line of sight communication.
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8. In free space, the ratio of frequency to the velocity of light gives the phase constant. State True/False.
a) True
b) False
View Answer

Answer: a
Explanation: The phase constant is given by the ratio of the frequency in radian/sec to the velocity of the wave propagating. In free space, the velocity is considered to be the velocity of light. Thus the statement is true.

9. The velocity of a wave travelling in the air medium without transmission lines or waveguides(wireless) is
a) 6 x 108
b) 3 x 108
c) 1.5 x 108
d) 9 x 108
View Answer

Answer: b
Explanation: In free space or air medium, the velocity of the wave propagating will be same as that of the light. Thus the velocity is the speed of light, V = c. It is given by 3 x 108m/s.
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10. The vectors of the electromagnetic wave propagation can be expressed in
a) Dot product
b) Cross product
c) Unit vector
d) Perpendicular vector
View Answer

Answer: b
Explanation: In an EM wave, the electric and the magnetic fields will be perpendicular to each other and with the direction of the propagation. Thus it can be expressed in cross product where iE x iH = iw. Here iE is the electric vector component, iH is the magnetic vector component and iw is the vector of the wave propagating.

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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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