Voortplantingssnelheid van elektromagnetische golven

Electromagnetic waves are consistent with Ampere's law.

Consider a plane wavefront traveling in the +x-direction. Over it, consider a rectangle in the xz-plane, with an area vector in the +y-direction.

The integration is performed counterclockwise around the rectangle.

The magnetic field is either zero or perpendicular to the length elements except for length "RS", where the field is parallel and contributes to the integral.

It implies that the right side of Ampere's law must also be non-zero. Therefore, the electric field must have a y-component that can provide a non-zero time derivative of electric flux.

It also establishes that the electric and magnetic fields must be mutually perpendicular.

The electric flux increases to a positive value in time "dt". The rate of change of electric flux can be substituted in Ampere's law.

Since electromagnetic waves are consistent with all of Maxwell's equations, the obtained expression is compared with the expression derived using Faraday's law, which gives the wave propagation speed in the vacuum.

Substituting the values of permeability and permittivity, the propagation speed is equal to the speed of light.