BEE Electromagnetic Fields and Waves 5

Question 1

The voltage standing-wave ratio (VSWR) on a transmission line terminated with a short circuit is:

Accepted Answer

Infinity (∞)

Answer

A short circuit creates a reflection coefficient Γ = -1 (|Γ| = 1), so VSWR = (1+1)/(1-1) → ∞.

Question 2

Snell's Law of refraction for electromagnetic waves at a planar interface states:

Accepted Answer

n₁ sin θ₁ = n₂ sin θ₂

Answer

The phase-matching condition at the boundary requires n₁ sin θ₁ = n₂ sin θ₂, identical to optics.

Question 3

Magnetic vector potential A is defined such that:

Accepted Answer

B = ∇ × A

Answer

Since ∇ · B = 0, B can always be written as the curl of a vector potential A.

Question 4

For a lossy transmission line, the propagation constant γ = α + jβ. At very high frequencies in a good conductor, α ≈ β. This means the wave:

Accepted Answer

Attenuates by 1/e over exactly one wavelength/2π

Answer

When α = β = 1/δ (skin depth formula), the wave decays by e⁻¹ over a distance equal to 1/α = δ ≈ λ/2π inside the conductor.

Question 5

Image theory in electromagnetics replaces a ground plane conductor with:

Accepted Answer

A mirror-image charge of opposite sign at the same depth below the surface

Answer

Image theory removes the conductor by placing an opposite charge at the mirror-image position, reproducing the correct boundary conditions above the surface.

BEE - Bachelor of Electrical Engineering Practice Test

BEE - Bachelor of Electrical Engineering Practice Test

BEE Electromagnetic Fields and Waves 5