Only the circuits that carry alternating currents radiate electromagnetic waves, hence if the charged particles are accelerated, the energy lost by the electrical circuits is represented by the electromagnetic waves. One way to accelerate the electric charges is to produce an alternating voltage in circuits.
Electromagnetic waves are not produced in circuits that carry charges whose velocities are constant. The circuits that are travelled by charges whose velocities are constant produce electric fields and magnetic fields.
The speed of electromagnetic waves depends on the permitivity and permeability of the medium in which they travel and the following Maxwell's equation relates the speed of light and the magnitudes of electric and magnetic fields of electromagnetic waves, such that:
`c = E/B`
c represents the speed of light
E represents the magnitude of electric field
B represents the magnitude of magnetic field