Electromagnetic Field Theory MCQ Questions & Answers

31

A 75 Ω transmission line is first short terminated and the minima locations are noted. When the short is replaced by a resistive load R_L, the minima locations are not altered and the VSWR is measured to be 3. The value of R_L is

A) 25 Ω B) 50 Ω C) 225 Ω D) 250 Ω

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Answer & Solution

Answer: Option A

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32

Which one of the following Maxwell's equations gives the basic idea of radiation?

A) \[\left. \begin{gathered} \nabla \times H = \frac{{\partial D}}{{\partial t}} \hfill \\ \nabla \times E = \frac{{ - \partial B}}{{\partial t}} \hfill \\ \end{gathered} \right\}\] B) \[\left. \begin{gathered} \nabla \times E = \frac{{ - \partial B}}{{\partial t}} \hfill \\ \nabla \cdot D = 0 \hfill \\ \end{gathered} \right\}\] C) \[\left. \begin{gathered} \nabla \cdot D = \rho \hfill \\ \nabla \cdot B = 0 \hfill \\ \end{gathered} \right\}\] D) \[\left. \begin{gathered} \nabla .B = 0 \hfill \\ \nabla \times H = \frac{{\partial D}}{{\partial t}} \hfill \\ \end{gathered} \right\}\]

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Answer & Solution

Answer: Option A

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33

Which one of the following is the correct expression for torque on a loop in magnetic field $$\overrightarrow B $$? (here $$\overrightarrow M $$ is the loop moment).

A) $$\overrightarrow T = \nabla .\overrightarrow B $$ B) $$\overrightarrow T = \overrightarrow M .\overrightarrow B $$ C) $$\overrightarrow T = \overrightarrow M \times \overrightarrow B $$ D) $$\overrightarrow T = \overrightarrow B \times \overrightarrow M $$

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Answer & Solution

Answer: Option C

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34

The signal propagation time between two ground stations in a synchronous satellite link is about

A) 50 ms B) 135 ms C) 270 ms D) None of these

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Answer & Solution

Answer: Option C

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35

A conductor having surface density σ is embedded in a dielectric medium of permittivity ε. The electric field in the medium is E. If it is known that the pressure p on the conductor surface is equal to the electric energy density in the medium, then p (in SI units) is given by:

A) $$\frac{{{\sigma ^2}}}{2}$$ B) $$\frac{\sigma }{{2\varepsilon }}$$ C) $$\frac{{{\sigma ^2}}}{{4\pi \varepsilon }}$$ D) $$\frac{{{\sigma ^2}}}{{2\varepsilon }}$$

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Answer & Solution

Answer: Option D

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36

A 50 Ω loss less transmission line is terminated in 100 Ω load and is exited by a 30 MHz source of internal resistance of 50 Ω. What should be the length of transmission line for maximum power transfer . . . . . . . .

A) 5.0 m B) 1.25 m C) 2.5 m D) 10.0 m

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Answer & Solution

Answer: Option B

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37

A transmission - line impairment is located 300 m from the source. For a velocity of propagation of 0.9 c, the time elapsed from the beginning of the pulse to reception of the echo is

A) 20.5 µs B) 22.22 ms C) 22.22 µs D) 25.75 µs

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Answer & Solution

Answer: Option C

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38

S parameters of a transmission line are S₁₁, S₁₂, S₂₁ and S₂₂. If the transmission line is symmetrical, what is the condition?

A) S₂₁ = -S₁₂ B) S₂₁ = S₁₂ C) S₁₁ = S₁₂ D) S₁₁ = S₂₂

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Answer & Solution

Answer: Option D

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39

For a reflection coefficient of 0.5, the value of SWR is

A) -1 B) 1 C) 2 D) 3

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Answer & Solution

Answer: Option D

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40

The electric field of a uniform plane electromagnetic wave in free space, along the positive x direction, is given by $$\overrightarrow E = 10\left( {{{\hat a}_y} + j{{\hat a}_z}} \right){e^{ - j25x}}.$$ The frequency and polarization of the wave, respectively, are

A) 1.2 GHz and left circular B) 4 Hz and left circular C) 1.2 GHz and right circular D) 4 GHz and right circular

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Answer & Solution

Answer: Option A

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Electromagnetic Field Theory MCQ Questions & Answers | ECE