Engineering Electromagnetics Fundamentals Flashcards

What is the divergence of the magnetic flux density B in free space?

Answer: ∇·B = 0

Maxwell's equation states that magnetic monopoles do not exist, so the divergence of B is always zero.

The capacitance per unit length of a coaxial cable with inner radius a and outer radius b, filled with dielectric ε, is:

Answer: 2πε / ln(b/a)

Applying Gauss's law to the coaxial geometry yields C/L = 2πε / ln(b/a).

In a good conductor, the skin depth δ is related to frequency f and conductivity σ as:

Answer: δ = √(2/ωμσ)

Skin depth is defined as δ = √(2/ωμσ), where ω = 2πf, showing fields decay exponentially into the conductor.

The Biot-Savart law gives the magnetic field contribution dH from a current element Idl as:

Answer: dH = (Idl × R̂) / (4πR²)

The Biot-Savart law states dH = (Idl × R̂)/(4πR²), giving field direction via the cross product.

What boundary condition applies to the tangential component of E at the interface between two dielectrics?

Answer: E_t1 = E_t2

The tangential component of E is continuous across any dielectric interface (no surface current).

The wave impedance η of a plane wave in a lossless medium with permittivity ε and permeability μ is:

Answer: η = √(μ/ε)

Intrinsic impedance is η = √(μ/ε); in free space this equals approximately 377 Ω.

The continuity equation relating current density J and charge density ρᵥ is:

Answer: ∇·J = -∂ρᵥ/∂t

The continuity equation ∇·J = -∂ρᵥ/∂t expresses conservation of electric charge.