This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Skin Effect”.
1. The skin effect is a phenomenon observed in
a) Insulators
b) Dielectrics
c) Conductors
d) Semiconductors
View Answer
Explanation: The skin of the conductor allows a certain amount of electromagnetic power to pass through it. This phenomenon is called the skin effect. This is the reason why, electromagnetic waves cannot travel inside a conductor.
2. The skin depth is measured in
a) Meter
b) Millimetre
c) Centimetre
d) Micrometer
View Answer
Explanation: The depth to which the electromagnetic waves pass through the conductor is very small. It is measured in μm.
3. The skin depth is calculated from the amplitude of the wave. State true/false
a) True
b) False
View Answer
Explanation: The skin depth is the measure of the depth to which the amplitude of an EM wave will reduce to 36.8% of its initial value. Thus it can be calculated if the initial amplitude is known.
4. The attenuation constant is 0.5 units. The skin depth will be
a) 0.5
b) 0.25
c) 2
d) 4
View Answer
Explanation: The skin depth is the reciprocal of the attenuation constant. Thus δ = 1/α. On substituting for α = 0.5, we get δ = 1/0.5 = 2 units.
5. Calculate the skin depth of a conductor, having a conductivity of 200 units. The wave frequency is 10 GHz in air.
a) 355.8
b) 3.558
c) 35.58
d) 0.3558
View Answer
Explanation: The skin depth is calculated by δ = 1/√(πfμσ), where f is the frequency, μ is the permeability and σ is the conductivity. For the given data, f = 10 x 109, μ = 4π x 10-7 in air and σ = 200, we get δ = 355.8 μm.
6. The effective skin resistance of a material with conductivity 120 and skin depth of 2μm is
a) 4.16 kilo ohm
b) 4.16 mega ohm
c) 41.6 kilo ohm
d) 41.6 mega ohm
View Answer
Explanation: The effective skin resistance is given by Rs = 1/δσ, where δ is the skin depth and σ is the conductivity. For the given data, δ = 2 x 10-6 and σ = 120, we get Rs = 1/(120x2x10-6) = 4.16 kilo ohm.
7. The skin depth is used to find which parameter?
a) DC resistance
b) AC resistance
c) Permittivity
d) Potential
View Answer
Explanation: Since the skin depth varies for different frequencies, it can be used to calculate the varying AC resistance for a material.
8. The relation between the skin depth and frequency is given by
a) Skin depth α f
b) Skin depth α 1/f
c) Skin depth α √f
d) Skin depth α 1/√f
View Answer
Explanation: The skin depth is given by δ = 1/√(πfμσ). Thus the relation between the skin depth and the frequency is, Skin depth α 1/√f.
9. A perfect dielectric acts as a
a) Perfect transmitter
b) Perfect reflector
c) Bad transmitter
d) Bad reflector
View Answer
Explanation: A perfect dielectric acts as a perfect transmitter. In other words, a wave incident on a perfect dielectric will transmit completely through it.
10. A perfect conductor acts as a
a) Perfect transmitter
b) Perfect reflector
c) Bad transmitter
d) Bad reflector
View Answer
Explanation: A perfect conductor acts as a perfect reflector. In other words, a wave incident on a perfect conductor will be totally reflected back into the same medium. There will be no skin effect.
11. The resultant electric field of two components in the x and y direction having amplitudes 6 and 8 respectively is
a) 100
b) 36
c) 64
d) 10
View Answer
Explanation: The resultant electric field of two components is given by E = √(Ex2 + Ey2). For the given data, the electric field will be E = √(62+82) = 10 units.
12. The skin depth of the wave having a frequency of 3MHz and a velocity of 12 m/s is
a) 2
b) 3
c) 4
d) 6
View Answer
Explanation: The velocity of a wave is the product of the frequency and the skin depth. Thus v = f.δ. To get δ, put v = 12 and f = 3MHz, we get δ = 12/(3×106) = 4 μm.
Sanfoundry Global Education & Learning Series – Electromagnetic Theory.
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