Editing Electromagnetic field (section)

=== Time-varying EM fields in Maxwell's equations ===
{{main|near and far field|near field optics|virtual particle|dielectric heating|Electromagnetic induction}}
An electromagnetic field very far from currents and charges (sources) is called [[electromagnetic radiation]] (EMR) since it radiates from the charges and currents in the source. Such radiation can occur across a wide range of frequencies called the [[electromagnetic spectrum]], including [[radio wave]]s, [[microwave]], [[infrared]], [[visible light]], [[ultraviolet light]], [[X-rays]], and [[gamma ray]]s. The many commercial applications of these radiations are discussed in the named and linked articles.

A notable application of visible light is that this type of energy from the Sun powers all life on Earth that either makes or uses oxygen.

A changing electromagnetic field which is physically close to currents and charges (see [[near and far field]] for a definition of "close") will have a [[dipole]] characteristic that is dominated by either a changing [[electric dipole]], or a changing [[magnetic dipole]]. This type of dipole field near sources is called an electromagnetic ''near-field''.

Changing {{em|electric}} dipole fields, as such, are used commercially as near-fields mainly as a source of [[dielectric heating]]. Otherwise, they appear parasitically around conductors which absorb EMR, and around antennas which have the purpose of generating EMR at greater distances.

Changing {{em|magnetic}} dipole fields (i.e., magnetic near-fields) are used commercially for many types of [[Electromagnetic induction|magnetic induction]] devices. These include motors and electrical transformers at low frequencies, and devices such as [[RFID]] tags, [[metal detector]]s, and [[MRI]] scanner coils at higher frequencies.