Electromagnetism is a theory unified by James Clerk Maxwell to explain the interrelationship between electricity and magnetism. At the heart of this theory is the notion of an electromagnetic field.

A stationary electromagnetic field stays bound to its origin. Examples of stationary fields are: the magnetic field around a wire carrying current or the electric field between the plates of a capacitor.

A changing electromagnetic field propagates away from its origin in the form of a wave. These waves travel in vacuum at the speed of light and exist in a wide spectrum of wavelengths. Examples of the dynamic fields of electromagnetic radiation (in order of increasing frequency): radio waves, microwaves, light (infrared, visible light and ultraviolet), x-rays and gamma rays. In the field of particle physics this electromagnetic radiation is the manifestation of the electromagnetic interaction between charged particles.

The subfield of electromagnetism dealing specifically with the rapidly changing electric and magnetic fields which constitute light, is called electrodynamics.

The whole of electromagnetism is governed by Maxwell's equations, which are compatible with and served as a motivation for the theory of relativity.

Electromagnetic Method

A geophysical method in which the magnetic and or electric fields resulting from generated surface currents are measured. Measurements may be made in the frequency domain at a number of frequencies, or the time domain at several time intervals after a transient pulse. Natural field methods such as magnetotellurics (MT) use natural magnetic and electromagnetic field as the source.

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