Definition of electromagnetic field
Electromagnetic field is a general term for the unity of internal and interdependent electric and magnetic fields. A time-varying electric field generates a magnetic field, and a time-varying magnetic field generates an electric field. The two are causal to each other and form an electromagnetic field. Electromagnetic fields can be caused by charged particles moving at variable speeds or by currents with varying strengths. Regardless of the cause, the electromagnetic field always propagates around at the speed of light to form electromagnetic waves. Electromagnetic field is the medium of electromagnetic action, with energy and momentum, is a form of existence of matter. The nature and characteristics of electromagnetic fields and the laws of their movement are determined by Maxwell's equations.