Electromagnetic radiation
Electromagnetism
Electricity · Magnetism
Electromagnetic radiation (sometimes ab-
breviated EMR and often simply called light)
is a ubiquitous phenomenon that takes the
form of self-propagating waves in a vacuum
or in matter. It consists of electric and mag-
netic field components which oscillate in
phase perpendicular to each other and per-
pendicular
to
the direction of
energy
propagation. Electromagnetic radiation is
classified into several types according to the
frequency of its wave; these types include (in
order of increasing frequency and decreasing
wavelength): radio waves, microwaves, tera-
hertz radiation, infrared radiation, visible
light, ultraviolet radiation, X-rays and gamma
rays. A small and somewhat variable window
of frequencies is sensed by the eyes of vari-
ous organisms; this is what we call the visible
spectrum, or light.
EM radiation carries energy and mo-
mentum that may be imparted to matter with
which it interacts.
Physics
Theory
Electromagnetic waves were first postu-
lated by James Clerk Maxwell and sub-
sequently confirmed by Heinrich Hertz. Max-
well derived a wave form of the electric and
magnetic equations, revealing the wave-like
nature of electric and magnetic fields, and
their symmetry. Because the speed of EM
waves predicted by the wave equation coin-
cided with the measured speed of light, Max-
well concluded that light itself is an EM
wave.
According to Maxwell’s equations, a time-
varying electric field generates a magnetic
field and vice versa. Therefore, as an
Shows three electromagnetic modes (blue,
green and red) with a distance scale in mi-
crometres along the x-axis.
oscillating electric field generates an oscillat-
ing magnetic field, the magnetic field in turn
generates an oscillating electric field, and so
on. These oscillating fields together form an
electromagnetic wave.
A quantum theory of
the
interaction
between electromagnetic radiation and mat-
ter such as electrons is described by the the-
ory of quantum electrodynamics.
Properties
T