This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Dielectric and Conductor Wave Propagation”.
1. In conductors, which condition will be true?
a) σ/ωε > 1
b) σωε > 1
c) σ/ωε < 1
d) σωε < 1
Explanation: For conductors, the conductivity will be maximum. Thus the loss tangent is greater than unity. This is given by σ/ωε >1.
2. For metals, the conductivity will be
Explanation: Metals are pure conductors. Examples are iron, copper etc. Their conductivity will be very high. Thus the metal conductivity will be infinity. Practically the conductivity of conductors will be maximum.
3. In conductors, which two parameters are same?
a) Wavelength and phase constant
b) Phase and attenuation constant
c) Attenuation constant and skin depth
d) Skin depth and wavelength
Explanation: In conductors, which are considered to be lossy, the attenuation and the phase constant are the same. It is given by α=β= √(ωμσ/2).
4. Calculate the velocity of wave propagation in a conductor with frequency 5 x 108 rad/s and phase constant of 3 x 108 units.
Explanation: The velocity of wave propagation is the ratio of the frequency to the phase constant. It is given by V = ω/β. On substituting the given values, we get V = 5/3 units.
5. Calculate the wavelength of the wave with phase constant of 3.14 units.
Explanation: The wavelength is the ratio of 2π to the phase constant β. On substituting for β = 3.14, we get λ = 2π/β = 2π/3.14 = 2 units.
6. For dielectrics, which two components will be in phase?
a) E and wave direction
b) H and wave direction
c) Wave direction and E x H
d) E and H
Explanation: In dielectrics, the electric and magnetic components E and H will be in phase with each other. This is due the variation in the permittivities and the permeabilities of the dielectric surfaces. The phase difference between E and H will be 0.
7. In perfect conductors, the phase shift between the electric field and magnetic field will be
Explanation: For perfect conductors, the electric and magnetic field E and H respectively vary by a phase of 45 degree. This is due to the polarisation phenomenon in the conductors, unlike dielectrics.
8. The expression for phase constant is given by
a) Phase constant β = ωμε
b) Phase constant ω = με
c) Phase constant β = ω√(με)
d) Phase constant β = 1/ωμε
Explanation: The phase constant is represented as β. It is a complex quantity representing the constant angle of the wave propagated. It is given by β = ω√(με).
9. In waveguides, which of the following conditions will be true?
a) V > c
b) V < c
c) V = c
d) V >> c
Explanation: In waveguides, the phase velocity will always be greater than the speed of light. This enables the wave to propagate through the waveguide. Thus V > c is the required condition.
10. The attenuation constant in lossless dielectrics will be
Explanation: In lossless dielectrics, the attenuation constant will not be same as the phase constant, unlike conductors. Also, due to the lossless behaviour, the attenuation will be nearly zero. Practically, zero attenuation is not possible.
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