# Electromagnetic Theory Questions and Answers – Properties of Waveguides

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

1. The waveguide is employed in the transmission lines, when operated at the range of
a) Hz
b) KHz
c) MHz
d) GHz

Explanation: Waveguides are employed for effective transmission, when the lines carry electromagnetic waves in the GHz range.

2. The cut off frequency for a waveguide to operate is
a) 3 MHz
b) 3 GHz
c) 6 MHz
d) 6 GHz

Explanation: The cut off frequency of the waveguide is 6 GHz. This is the frequency at which the waveguide will start to operate.

3. In rectangular waveguides, the dimensions a and b represent the
a) Broad wall dimensions
b) Broad wall and side wall dimension respectively
c) Side wall and broad wall dimension respectively
d) Side wall dimensions

Explanation: In rectangular waveguide, the a parameter is the broad wall dimension of the waveguide and the b parameter is the side wall dimension of the waveguide. Always, a > b in a waveguide.

4. The Bessel function is denoted by
a) Jn(ha)
b) Jm(ha)
c) Jn(hb)
d) Jm(hb)

Explanation: The Bessel function is used in the circular waveguides. Normally Jn(ha) = 0. Here n is the order of the Bessel function.

5. In a waveguide, always which condition holds good?
a) phase velocity = c
b) phase velocity greater than c
c) phase velocity lesser than c
d) group velocity = c

Explanation: In air medium, the phase velocity is assumed to be the speed of light. For waveguides, the phase velocity is always greater than the speed of the light.
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6. The group wavelength is greater than the wavelength at any point. State true/false.
a) True
b) False

Explanation: In a waveguide, the phase velocity is greater than the velocity of light. Thus the group velocity will be less. This implies the group wavelength will be greater than the wavelength at any point.

7. Find the group wavelength of a wave, given that the group phase constant is 6.28 units.
a) 2
b) 3.14
c) 6.28
d) 1

Explanation: The group wavelength is given by λg = 2π/βg, where βg is the group wavelength of the wave. On substituting for βg = 6.28, we get group wavelength as unity.

8. The phase velocity of a wave with frequency of 15 radian/sec and group phase constant of 2 units is
a) 30
b) 15
c) 7.5
d) 2/15

Explanation: The phase velocity of a wave is given by Vp = ω/βg. on substituting for ω = 15 and βg = 2, we get phase velocity as 15/2 = 7.5 units.

9. The modes in a material having a V number of 20 is
a) 20
b) 400
c) 200
d) 100

Explanation: The relation between the modes and the V number is given by m = v2/2. Given that v = 20, we get m = 202/2 = 200 modes.

10. The number of modes is given as 50, find the V number.
a) 5
b) 10
c) 50
d) 2500

Explanation: The relation between the modes and the V number is given by m = v2/2. Given that m = 50, we get v2 = 2 x 50 = 100. The V number is 10.

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