About Electromagnetic Fields

An electromagnetic field is the combination of force fields that arise from static and moving charges. Although electric and magnetic fields are interrelated mathematically and physically, the term "electromagnetic field" implies two fields that can be treated individually.

Electric Field

• The definition of the electric field is force per unit charge. It is described mathematically as a vector field. Physically, it is a non-visible force field that arises from the presence of a charge or a collection of charges. Electric field lines emanate outward and radially from positive charges, terminating on negative charges. When the charge distribution is largely static, the behavior of the field does not change over time and no magnetic field is generated.

Magnetic Field

• A magnetic field arises when a charge distribution changes as a function of time. The most prominent example of this relationship is current flow, where a magnetic field circles about the axis of the current's propagation, directionally such that a current induced by this field would flow in a direction that opposes the original current. Hence, magnetic fields are consequences of nature's resistance to change.

How Electric and Magnetic Fields Relate

• The time rate of change of a magnetic field is equal to the curl of the electric field when both are generated by the same source. These interrelated fields travel as waves more commonly called radio waves or "EM" waves, propagating through space perpendicularly to one another.