BEE Electromagnetic Fields and Waves 4

Question 1

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

Accepted Answer

(L/λ)²

Answer

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

Question 2

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

Accepted Answer

Electric charge

Answer

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

Question 3

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

Accepted Answer

ln(b/a)

Answer

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

Question 4

The Biot–Savart Law is used to find:

Accepted Answer

Magnetic field produced by a steady current element

Answer

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

Question 5

The directivity of an isotropic radiator is:

Accepted Answer

1 (0 dBi)

Answer

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

BEE - Bachelor of Electrical Engineering Practice Test