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Electric Field

Electromagnetic fields are caused by electric charges at rest and in motion. Positive and negative electric charges are sources of the electric fields and moving electric charges yielding a current is the source of magnetic fields. Time-varying electric and magnetic fields are coupled in an electromagnetic field radiating from the source
 
Electromagnetic fields are divided into four different quantities:the magnetic flux density B with the unit T (Tesla or volt-second per square meter) the magnetic field intensity H with the unit A/m (Ampere per meter) the electric field intensity E with the unit V/m (Volt per meter) the electric flux density D with the unit C/m2 (Coulomb per square meter) A time-varying E and D will give rise to B and H, and vice versa where the relation depends on the properties of the medium. Far enough from the source the magnetic field, H, will be perpendicular to the electric field, E, and both are normal to the direction of propagation.