Question

what is the difference between a constant and changing magnetic and electric field? How does an electromagnetic wave form?

Answer 1

Theconstant electric and magnetic fields is generated by sources – electric charges for electric field and currents for magnetic field. According to equation of electrodynamics (Maxwell’s equations) the changing magnetic field generates electric field and changing electric field generates magnetic. These fields are vortical, i.e. have no sources. Therefore they could exist independently from background, being converted into each other. Exactly this is the electromagnetic wave.