# Microwave Engineering Questions and Answers – Co-axial Lines Field Analysis

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This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Co-axial Lines Field Analysis”.

1. The expression for conductance G of a coaxial transmission line with outer radius ‘b’ and inner radius ‘a’ is given by:
a) 2πωε”/ (ln b/a)
b) (R/2π)(1/a+1/b)
c) Rb/πa
d) 2Rb/a

Explanation: The conductance G of a coaxial transmission line is 2πωε”/ (ln b/a). Conductance of the transmission line is inversely related to the conductance of the transmission line.

2. Expression for resistance R of a coaxial transmission line outer radius b and inner radius a is:
a) Rs/2π ( 1/a+1/b)
b) 2πω∈”/ln⁡(b/a)
c) μ/π cos-1(b/a)
d) πϵ’/cosh-1(b/a)

Explanation: Resistance R of a coaxial transmission line is Rs/2π ( 1/a+1/b). Here a and b are the outer and inner radius of the transmission line. Rs are the series resistance of the coaxial cable.

3. If the outer and the inner diameter of a coaxial transmission line are 20 mm and 10 mm respectively, then the inductance /m of the transmission line is:
a) 0.13 µH
b) 0.2 µH
c) 0.3 µH
d) 0.1 µH

Explanation: Inductance of a coaxial transmission line is µ*ln (b/a)/ 2π. Substituting the given values in the equation for inductance, the inductance is 0.13 µH.

4. If the outer circumference and the inner circumference of a transmission line are 40π and 25π units respectively, then the capacitive reactance of the coaxial transmission line is:
a) 0.376 nF
b) 0.45 nF
c) 0.9 nF
d) none of the mentioned

Explanation: Capacitance of a coaxial transmission line is given by the expression 2π∈/ln (b/a). Computing the capacitance from this equation and then computing the capacitive reactance, the coaxial line has a capacitive reactance 0.376 nF.

5. For a 2 wire transmission line, if the complex part of permittivity is 2.5, then the given distance between the 2 wires is 10mm and operated at a frequency of 1.2 MHz and the radius of the line being 5mm, then the conductance of the transmission line is:
a) 0.2 µH
b) 0.1 µH
c) 0.5 µH
d) 1 µH

Explanation: For a two wire transmission line, inductance of the line is given by π∈/ cosh-1(D/ 2a). Substituting the given values in the above equation, the conductance of the line is 0.2 µH.

6. Characteristics impedance of a coaxial line with external and inner diameter 5mm is:
a) 40 Ω
b) 41.58 Ω
c) 47.78 Ω
d) 54.87 Ω

Explanation: Characteristic impedance of the coaxial line is given by the expression ln (b/a)/ 2π. Substituting the given values in the above expression, the characteristic impedance is 41.58 Ω.

7. The characteristic impedance of the transmission line if the outer diameter and inner diameter of the transmission line is 20 mm and 10 mm respectively, given the intrinsic impedance of the medium is 377 Ω, then the characteristic impedance of the transmission line is:
a) 41.58 Ω
b) 50 Ω
c) 377 Ω
d) None of the mentioned

Explanation: Characteristic impedance of the coaxial line is given by the expression ln (b/a)/ 2π. Substituting the given values in the above expression, the characteristic impedance 41.58 Ω.

8. Flow of power in transmission line takes place through:
a) Electric field and magnetic field
b) Voltage and current
c) Voltage
d) Electric field

Explanation: In a transmission line, flow of power takes place through propagation of electric field and magnetic field. Alternating electric field and alternating magnetic field propagates EM wave transmitting power.

9. When a transmission line is exited by a source, total power supplied is delivered to the load.
a) True
b) False

Explanation: When a transmission line is excited by the source, entire power is not delivered to the load due to the various types of losses that occur in the transmission line.

10. Expression for propagation constant. γ In terms of ω is:
a) √ω2µ∈
b) ω2µ∈
c) – ω2µ∈
d) None of the mentioned

Explanation: Propagation constant γ for a transmission line is dependent on the operating frequency of the transmission line, and the permittivity and permeability of the medium.

Sanfoundry Global Education & Learning Series – Microwave Engineering.
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