This set of Electromagnetic Theory Questions and Answers for Entrance exams focuses on “Transmission Line Secondary Parameters”.
1. The wavelength of a line with a phase constant of 6.28 units is
Explanation: The wavelength and the phase constant are related by λ = 2π/β, where β is given as 6.28. On substituting for β, we get λ = 2π/6.28 = 1 unit.
2. The wavelength of a wave with a frequency of 6 GHz in air is
Explanation: The wavelength is given by the ratio of the velocity to the frequency of the wave. In air medium, the velocity can be assumed as the speed of light. On substituting for v and f, we get λ = v/f = 3×108/6×109 = 0.05 units.
3. The phase constant of a wave with a wavelength of 2 units is given by
Explanation: The phase constant is given by β = 2π/λ. On substituting for λ = 2, we get β = 2π/2 = 3.14 units.
4. The frequency of a wave travelling in a transmission line with velocity 4 x 108 and wavelength 3 units is
a) 0.75 GHz
b) 0.133 GHz
c) 7.5 GHz
d) 1.33 GHz
Explanation: The frequency and wavelength relation is given by f = v/λ. On substituting for v and λ, we get f = 4 x 108/3 = 0.133 GHz.
5. The velocity and phase constant relation is given by
a) V = ω/β
b) V = ωβ
c) V = β/ω
d) Vωβ = 1
Explanation: The velocity of a wave is the ratio of the frequency in radian/second to the phase constant. It is given by V = ω/β.
6. Find the phase constant of a wave travelling with a velocity of 1.2 x 108 and a frequency of 7.5 giga radian/sec
Explanation: The phase constant is given by β = ω/v, from the definition of phase constant and velocity. On substituting for ω = 7.5 x 109 and v = 1.2 x 108, we get the phase constant β = 7.5 x 109/1.2 x 108 = 62.5 units.
7. The electrical length in a transmission line refers to the
a) Product of attenuation constant and length
b) Ratio of attenuation constant and length
c) Product of phase constant and length
d) Ratio of phase constant and length
Explanation: The electrical length in a transmission line refers to the product of the attenuation constant α and the length of the line l. It is given by αl.
8. The unit of attenuation constant is
d) No unit
Explanation: Attenuation constant is the measure of the power loss of the wave during its transmission. It is expressed in terms of neper and 1 neper= 8.686 decibel/m.
9. The attenuation constant causes phase distortion and the phase constant causes frequency distortion. State True/False.
Explanation: There are always some distortions, even in the perfect transmission line. This is due to the variation of the secondary parameters. The attenuation constant causes the frequency distortion, whereas the phase constant causes the phase distortion.
10. The propagation constant of a wave with attenuation and phase constant given by 2 and 3 respectively is
a) 2 – 3j
b) 3 – 2j
c) 2 + 3j
d) 3 + 2j
Explanation: The propagation constant is given by γ = α + jβ. Given that α = 2 and β = 3. Thus we get the propagation constant as γ = 2 + 3j.
11. The velocity of wave in the air medium is
a) 1 x 108
b) 1.5 x 108
c) 3 x 108
d) 1 x 109
Explanation: The light is travelling at its fastest speed in air medium. Thus the velocity of a wave in the air medium is assumed to have the speed of light. It is given by c = 3 x 108.
12. Identify the secondary parameter from the options given below.
c) Phase constant
Explanation: Primary parameters are directly observed from the circuit characteristics. Secondary parameters are derived or calculated from the primary parameters. R, L, C, G are primary parameters, whereas α, β, γ, Zo are secondary parameters.
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