A plane electromagnetic wave in a homogeneous medium has electric field E= xE x e-j( t- z). The real quantities () and E x are known. Which CANNOT be determined?

GATE 2016 EC (EC2) – Question 34

Electromagnetics · Plane Waves and Properties · 1 mark · Multiple choice

A plane electromagnetic wave in a homogeneous medium has electric field $\mathbf E=\hat{\mathbf x}E_x e^{-j(\omega t-\beta z)}$. The real quantities $\beta(\omega)$ and $E_x$ are known. Which CANNOT be determined?

type of polarization
group velocity
phase velocity
power flux through the plane z=0

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Correct answer: (D) power flux through the plane z=0

Explanation

Only the x-directed field is present, so the polarization is linear. The known dispersion relation gives phase velocity $v_p=\omega/\beta$ and group velocity $v_g=d\omega/d\beta$.

Power flux needs the magnetic field as well as the electric field, or equivalently the medium's wave impedance. The propagation constant alone does not separate permittivity and permeability to determine that impedance. Thus **D** cannot be determined.

GATE 2016 EC (EC2) – Question 34

Explanation

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