BEE Bachelor of Electrical Engineering Electromagnetic Fields and Waves Questions and Answers

Question 1

An electromagnetic plane wave propagates from a lossless medium into a lossy medium. Which of the following effects is expected to occur?

Accepted Answer

The wave's amplitude will attenuate as it travels through the lossy medium.

Answer

In a lossy medium, which has non-zero conductivity, part of the electromagnetic wave's power is converted into heat, causing the wave's amplitude to decrease or attenuate as it propagates. The frequency of the wave remains constant when moving between media. The speed of the wave is typically lower in a denser, lossy medium, and polarization change is not a guaranteed effect of entering a lossy medium.

Question 2

A transmission line with a characteristic impedance of 50 Ω is terminated with a load impedance of 100 Ω. What is the Voltage Standing Wave Ratio (VSWR) on the line?

Accepted Answer

2.0

Answer

First, calculate the reflection coefficient (Γ) using the formula: Γ = (ZL - Z0) / (ZL + Z0). Here, ZL = 100 Ω and Z0 = 50 Ω. So, Γ = (100 - 50) / (100 + 50) = 50 / 150 = 1/3. Next, calculate the VSWR using the formula: VSWR = (1 + |Γ|) / (1 - |Γ|). VSWR = (1 + 1/3) / (1 - 1/3) = (4/3) / (2/3) = 2.0. A VSWR of 2.0 indicates a mismatch where the maximum voltage on the line is twice the minimum voltage.

Question 3

Which of Maxwell's equations states that magnetic monopoles do not exist and that magnetic field lines must form closed loops?

Accepted Answer

Gauss's Law for Magnetism

Answer

Gauss's Law for Magnetism, expressed in differential form as ∇ ⋅ B = 0, mathematically states that the divergence of the magnetic field is zero. This implies there are no sources or sinks (i.e., monopoles) for magnetic fields, and consequently, magnetic field lines must always form continuous, closed loops.

Question 4

In a hollow rectangular waveguide, which mode of propagation is characterized by having no electric field component in the direction of wave propagation and is typically the dominant mode?

Accepted Answer

Transverse Electric (TE)

Answer

Transverse Electric (TE) modes are characterized by the electric field vector being entirely perpendicular (transverse) to the direction of wave propagation. In standard rectangular waveguides, the TE10 mode has the lowest cutoff frequency and is therefore the dominant mode. TEM modes cannot propagate in a hollow single-conductor waveguide, and TM modes have a magnetic field that is entirely transverse.

Question 5

An engineer is designing a high-frequency circuit on a printed circuit board (PCB). As the frequency of the signals increases, the current tends to flow only near the surface of the copper traces. What is this phenomenon called?

Accepted Answer

Skin Effect

Answer

The skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor and decreases with greater depths. This effect becomes more pronounced as the frequency increases, reducing the effective cross-section of the conductor and increasing its AC resistance.

BEE - Bachelor of Electrical Engineering Practice Test

BEE - Bachelor of Electrical Engineering Practice Test

BEE Bachelor of Electrical Engineering Electromagnetic Fields and Waves Questions and Answers