# Electromagnetic Theory Questions and Answers – Transients

This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Transients”.

1. The resonant circuit in a waveguide refers to the
a) Tank circuit
b) RC circuit
c) Bridge circuit
d) Attenuator circuit

Explanation: The resonant circuit refers to the tank circuit. It is parallel combination of an inductor and a capacitor.

2. When a waveguide is terminated, the mode of the guided termination will be
a) zero
b) non-zero
c) infinite
d) does not exist

Explanation: A waveguide mode with a guided termination is represented by TEmnp and TMmnp. Here m and n are the orders of the waveguide and p is the order of the resonant cavity. It is always a non-zero value.

3. The cut off frequency of a waveguide with resonant cavity is given by
a) V√((m/a)2 + (n/b)2 + (p/d)2)/2
b) V√((m/a)2 + (n/b)2 + (p/d)2)
c) 2V√((m/a)2 + (n/b)2 + (p/d)2)
d) V√((m/a) + (n/b) + (p/d))/2

Explanation: The cut off frequency of the waveguide of dimensions a x b with the resonant cavity of dimension d is given by fc = √((m/a)2 + (n/b)2 + (p/d)2)/2. Here m and n are the orders of the waveguide, p is the order of the cavity and v is the velocity.

4. The power of a wave in a transmission line, when the current and the resistance are 5A and 120 ohm respectively is
a) 3000
b) 4000
c) 2000
d) 1500

Explanation: The power of a line is given by P = I2R. On substituting for I = 5 and R = 120, we get P = 52 x 120 = 3000 units.

5. The power of a wave having a magnetic field intensity of 2.5 units is
a) 1.17 kilo watt
b) 1.17 mega watt
c) 1.17 watt
d) 11.7 watt

Explanation: The power of a wave is given by P = 0.5 η H2, where η is the intrinsic impedance and H is the magnetic field intensity. On substituting for η = 377 and H = 2.5, we get P = 0.5 x 377 x 2.52 = 1.17 kilo watts.
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6. The power of a wave having an electric field strength of 12.8 units is
a) 0.217
b) 0.721
c) 0.127
d) 0.172

Explanation: The power of a wave is given by P = 0.5 E2/η, where E is the electric field intensity and η is the intrinsic impedance. On substituting for E = 12.8 and η = 377, we get P = 0.5 x 12.82/377 = 0.217 units.

7. The form or mode of propagation is determined by which factors?
a) Type of excitation device
b) Location of excitation device
c) Type and location of the excitation device
d) Waveguide characteristics

Explanation: The form and the mode of propagation of the wave in a waveguide is determined by the type and location of the excitation device.

8. The phase of the wave after the installation of the guided terminations will be
a) 0
b) 45
c) 90
d) 180

Explanation: Using a guided termination, the guides serves as a reflector. If the distance between the exciter and the wall is properly adjusted, the transmitted and the reflected wave will be in phase.

9. The exciter of the waveguide in a transmission line is the
a) Transmitter
c) Transponder
d) Antenna

Explanation: The waveguide is usually excited by the antenna rod. The reflection depends on the phase of excitation and the antenna current.

10. A waveguide imitates which type of filter characteristics?
a) Low pass filter
b) High pass filter
c) Band pass filter
d) Band reject filter

Explanation: A waveguide passes only high frequency waves (in GHz range) and attenuates low frequencies. This is the characteristic of a high pass filter.

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