This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Planes Waves in Good Conductor”.
1. For conductors, the loss tangent will be
Explanation: In conductors, the conductivity will be more. Thus the loss tangent σ/ωε will be maximum.
2. In metals, the total permittivity is
a) Absolute permittivity
b) Relative permittivity
c) Product of absolute and relative permittivity
Explanation: The total permittivity is the product of the absolute and the relative permittivity. For metals or conductors, the relative permittivity is unity. Thus the permittivity is simply the absolute permittivity.
3. The total permeability in a conductor is
a) Absolute permeability
b) Relative permeability
c) Product of absolute and relative permeability
Explanation: The total permeability is the product of the absolute and the relative permeability. For metals or conductors, the relative permittivity is not unity. Thus the permittivity is the product of absolute and relative permeability.
4. Calculate the phase constant of a conductor with attenuation constant given by 0.04 units.
Explanation: The phase constant and the attenuation constant are both the same in the case of conductors. Given that the attenuation constant is 0.04, implies that the phase constant is also 0.04.
5. Calculate the attenuation constant of a conductor of conductivity 200 units, frequency 1M radian/s in air.
Explanation: The attenuation constant of a conductor is given by α = √(ωμσ/2). On substituting ω = 106, σ = 200 and μ = 4π x 10-7, we get α = 11.2 units.
6. The skin depth of a conductor with attenuation constant of 7 neper/m is
Explanation: The skin depth is the measure of the depth upto which an EM wave can penetrate through the conductor surface. It is the reciprocal of the attenuation constant. On substituting for α = 7, we get δ = 1/α = 1/7 units.
7. The expression for velocity of a wave in the conductor is
a) V = √(2ω/μσ)
b) V = √(2ωμσ)
c) V = (2ω/μσ)
d) V = (2ωμσ)
Explanation: The velocity is the ratio of the frequency to the phase constant. In conductors, the phase constant is given by √(ωμσ/2). On substituting for β,ω in v, we get v = √(2ω/μσ) units.
8. In conductors, the E and H vary by a phase difference of
Explanation: The electric and magnetic component, E and H respectively have a phase difference of 45 degrees. This is due to the wave propagation in conductors in the air medium.
9. EM waves do not travel inside metals. State True/False.
Explanation: The conductors or metals do not support EM wave propagation onto them due the skin effect. This is the reason why mobile phones cannot be used inside lifts.
10. The propagation constant of the wave in a conductor with air as medium is
Explanation: The propagation constant is the sum of the attenuation constant and the phase constant. In conductors, the attenuation and phase constant both are same and it is given by √(ωμσ/2). Their sum will be √(ωμσ), is the propagation constant.
11. An example for electromagnetic wave propagation is
b) electric fan
c) mobile transponder
d) relays in actuators
Explanation: The refrigerator, electric fan and relays are electrical devices. They do not use electromagnetic energy as medium of energy transfer. The mobile transponder is an antenna, which uses the EM waves for communication with the satellites.
12. The phase shift in the electric and magnetic fields in an EM wave is given by which parameter?
a) phase constant
b) attenuation constant
c) propagation constant
d) intrinsic impedance
Explanation: The intrinsic impedance in a conductor is given by η = √(ωμ/2σ) x (1+j). The phase shift is represented by the 1+j term. In polar form it indicates 45 degree phase shift.
Sanfoundry Global Education & Learning Series – Electromagnetic Theory.
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