Electromagnetic Fields and Waves Flashcards

An electric dipole antenna of length L << λ radiates power proportional to:

Answer: (L/λ)²

Radiated power from a Hertzian dipole is proportional to (L/λ)², making short antennas very inefficient radiators.

The continuity equation ∇ · J + ∂ρ/∂t = 0 expresses conservation of:

Answer: Electric charge

The continuity equation is the mathematical statement of charge conservation, linking current density to charge density.

In a coaxial transmission line with inner radius a and outer radius b, the characteristic impedance Z₀ is proportional to:

Answer: ln(b/a)

Z₀ = (η/2π)ln(b/a) for a coaxial line, where η is the intrinsic impedance of the fill medium.

The Biot–Savart Law is used to find:

Answer: Magnetic field produced by a steady current element

Biot–Savart gives dH = (I dL × âR)/(4πR²) for the differential H-field from a current element.

The directivity of an isotropic radiator is:

Answer: 1 (0 dBi)

An isotropic antenna radiates equally in all directions, so its directivity is defined as unity (0 dBi).

The phase velocity of a wave in a non-magnetic medium with relative permittivity εr is:

Answer: c/√εr

Phase velocity vp = 1/√(με) = c/√(μrεr); for non-magnetic media (μr = 1), vp = c/√εr.

Which of these is NOT one of Maxwell's four equations?

Answer: F = q(E + v × B)

F = q(E + v × B) is the Lorentz force law, a separate result, not one of Maxwell's four equations.