Physics
Electromagnetic Waves
Move charged particles with the mouse and watch an approximate retarded electromagnetic field propagate through a configurable medium. Show E and B vectors on a plane or throughout the volume, build a simple dipole antenna, and compare how permittivity and permeability change wave speed, impedance, and wavelength.
Vectors & plane
Medium & source
Charges
n = √(εᵣ μᵣ)1.000
v = c / n3.00e8 m/s
η = η₀√(μᵣ/εᵣ)376.7 Ω
λ = v / f3.00 m
Simulation time0.00
Left-drag a charge to move it, or use its x·y·z sliders to place it anywhere, including off the sampling plane, where the field then tilts out into 3D. Right-drag (or Alt/Shift-drag) to orbit, scroll to zoom. The field is an educational retarded-source approximation, not a full FDTD Maxwell solver.
What to observe
- Grab the charge and jiggle it back and forth. A sharp kink races outward at the wave speed: you are watching a charge radiate. Let it sit still and the field just stands there, only acceleration makes waves.
- Hit Dipole antenna and switch to E + B. Out in the far field the red and blue arrows turn transverse: E and B end up perpendicular to each other and to the outward direction, the fingerprint of a real electromagnetic wave.
- Raise the permittivity εᵣ or permeability μᵣ. The speedv = c/n drops, the wavelength shrinks to keep up, and the impedance η shifts, exactly what a denser optical medium does to light.
- Turn up the loss σ and the ripples fade with distance, like a signal dying in a lossy material. Keep sampling on Plane: filling all of space with arrows quickly turns into unreadable spaghetti.
Shortcuts: space run/pause · s step · r reset · f fullscreen