Physics

Electromagnetic Waves

Shake a charge and watch its field ripple outward as a glowing shell, at the speed the medium allows. Build a dipole antenna to see its radiation glow as a doughnut round the wire, with E and B turning transverse in 3D, or switch to statics for the Coulomb field lines of fixed charges and the magnetic circles round a wire.

electric field Emagnetic field Bfield strength √(εE² + B²/μ)

Drag a charge to move it · drag empty space to orbit · scroll to zoom

Wave speed in this medium—

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Scene

Show

Field strength

Fog opacity 1.00

thindense

Arrows

Plane

Plane offset 0.0

Density 15 × 15

Wavefronts

Permittivity ε_r 1.0

Permeability μ_r 1.0

Loss σ 0.00

Antenna frequency f 0.55

n = √(ε_r μ_r)—

v = c / n—

η = η₀ √(μ_r / ε_r)—

λ = v / f—

What to observe

Shake the charge and a glowing shell races outward at the wave speed: the charge radiates. Held still, its field just stands there, because only acceleration makes waves.
The dipole antenna's radiation glows as a doughnut, dark along the antenna's own axis, with shells half a wavelength apart streaming outward. Far out, E, B and the direction of travel are all at right angles: the wave is transverse.
Raise ε_r and the wave slows to c/n. The rings, one wavelength apart, crowd together and the impedance η drops.
In Statics the number of lines on a charge is proportional to |q|, so a −2 next to a +1 draws extra lines in from infinity. The B circles spread out with distance because B falls as 1/r.

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