This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Lossless and Distortionless Line”.
1. The transmission line is said to be lossless when the
a) Conductor is perfect and dielectric is lossless
b) Conductor is perfect and dielectric is lossy
c) Conductor is imperfect and dielectric is lossy
d) Conductor is imperfect and dielectric is lossless
View Answer
Explanation: Lossless transmission line refers to a line with no losses or attenuation. This is possible only when the conductor is perfect and the dielectric is lossless.
2. The resistance of a lossless transmission line is
a) 0
b) 1
c) -1
d) Infinity
View Answer
Explanation: The lossless transmission line will have minimal loss of power. Thus in the ideal cases, the resistance is assumed to be zero.
3. Which two parameters given below are zero in the lossless line?
a) L, C
b) C, G
c) G, α
d) R, L
View Answer
Explanation: Due to the minimal losses in the lossless transmission line, the parameters of conductance and attenuation constant are assumed to be zero. Practically, a lossless line is not possible.
4. The characteristic impedance of the line having primary constants L and C as 35 milli henry and 70 micro farad respectively is
a) 500
b) 22.36
c) 125
d) 50
View Answer
Explanation: The characteristic impedance of a lossless line is given by Zo = √(L/C). On substituting for L = 35 x 10-3 and C = 70 x 10-6, we get Zo = √(500) = 22. 36 ohm.
5. The attenuation constant is measured in the units of
a) Ohm
b) Neper
c) Decibel
d) Radian/sec
View Answer
Explanation: The attenuation is the loss of power due to the transmission. It is measured in the Neper units. 1 neper = 8.68 decibel/m.
6. The velocity of the transmission line with a frequency of 35 radian/s and phase constant of 68.5 is
a) 1.95
b) 2.36
c) 4.56
d) 3.48
View Answer
Explanation: The velocity of the wave in a transmission line is the ratio of the frequency to the phase constant. Thus v = ω/β. On substituting for ω = 35 and β = 68.5, we get v = 68.5/35 = 1.95 units.
7. The condition that holds good in a distortionless transmission line is
a) R/L = G/C
b) RL = GC
c) L/R = C/G
d) RG/LC
View Answer
Explanation: For a distortionless transmission line, the primary constants are related by R/L = G/C.
8. Given that R = 20 ohm, L = 40 mH, C = 40 μF, G = 0.02 mho. Find whether the line is distortionless or not.
a) Distorted line
b) Distortionless line
c) All of the mentioned
d) None of the mentioned
View Answer
Explanation: For a distortionless line, the condition R/L = G/C must be true. On substituting for R = 20, L = 40 mH, C = 40 μF, G = 0.02, we get R/L = 500 and G/C = 500. Thus the line is distortionless.
9. For R= 20 ohm and G= 0.8 mho, the attenuation constant will be
a) 16
b) 4
c) 2
d) 32
View Answer
Explanation: The attenuation constant is given by α = √(RG), where R and G is the resistance and conductance respectively. On substituting for R = 20 and G = 0.8, we get α = √(20 x 0.8) = 4 units.
10. The velocity of an electromagnetic wave with frequency 6MHz and a skin depth of 1.6 μm.
a) 3.75
b) 0.26
c) 9.6
d) 7.8
View Answer
Explanation: The velocity of a wave is the product of the frequency and the skin depth. It is given v = f. δ. On substituting for f = 6 x 106 and δ = 1.6 x 10-6, we get v = 6 x 106 x 1.6 x 10-6 = 9.6 units.
11. The characteristic impedance of the transmission line with R= 45 ohm and G= 0.45 mho is
a) 100
b) 1
c) 0.1
d) 10
View Answer
Explanation: The characteristic impedance in terms of R, G is Zo = √(R/G). On substituting for R = 45 and G = 0.45, we get Zo = 10 units.
12. The distortionless line is one in which the attenuation constant and phase constant are independent of the frequency. State true/false.
a) True
b) False
View Answer
Explanation: In a distortionless line, the attenuation constant is independent of the frequency and the phase constant is linearly dependent of the frequency.
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