Question 1

Why are the E and B fields perpendicular in an EM wave?

Accepted Answer

Maxwell's equations require that for a plane wave, the electric field E, magnetic flux density B, and propagation direction k form a mutually orthogonal triad. This follows directly from Faraday's law (∇×E = -∂B/∂t) and the Ampere-Maxwell law applied to a plane wave solution.

Question 2

What changes when the wave travels through glass, water, or tissue?

Accepted Answer

The relative permittivity εr and permeability μr reduce the phase velocity to v = c/√(εrμr). Glass (εr≈4–9) slows light to about half to one-third of c — the origin of refraction. Biological tissue has high permittivity (εr≈50–80) and conductivity, causing rapid attenuation (shallow skin depth).

Question 3

What does the Poynting vector represent?

Accepted Answer

S = E × B / μ₀ gives the instantaneous power density (W/m²) of the electromagnetic field. The solar irradiance at Earth's orbit is about 1361 W/m². Microwave ovens operate at 2.45 GHz and deliver roughly 1000 W of energy to food via the Poynting vector.

Question 4

What is the difference between linear and circular polarization?

Accepted Answer

In linear polarization, the E-field vector oscillates in a fixed plane. In circular polarization, the E-field tip rotates at constant angular speed, formed by combining two equal-amplitude components with a 90° phase difference. Satellite TV dishes and modern smartphone AMOLED displays use circular polarization to reduce glare and interference.

Electromagnetic Wave Simulator — E & B Field Visualization

Key Equations