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Electromagnetic radiation
[[File:EM Spectrum Properties edit.svg|thumb|right]]
'''Electromagnetic radiation''' comes in many different types, although the differences between them are quantitative rather than qualitative.  This teaching aid lists the different types that are generally recognised.

Electromagnetic radiation is a wave, so has a wavelength &lambda; and a frequency &nu;.  It is also composed of particles called photons, and each photon has an energy E.  These three quantities are related, and any of them may be used to define the type of ratdiation.

== Units of measurenent ==
Scientists usually use SI units.  The unit of frequency is the hertz (Hz), one cycle per second, named after Heinrich Hertz.  For our purposes, we shall use much higher frequencies.  One thousand Hz is a kHz (kilohertz); one thousand kHz is a MHz (megahertz); one thousand MHz is a GHz (gigahertz); one thousand GHz is a THz (terahertz).

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There is no lower boundary to the wavelength hence no upper bound to frequency or photon energy.  In October 2011, photons with energies exceeding 100 billion eV, i.e. over a million times the lower limit, were detected from the Crab pulsar.[http://www.sciencedaily.com/releases/2011/10/111006141358.htm]

== See also ==
* [[Electromagnetic fields and waves]]

[[Category:Resources last modified in April 2012]]
[[Category:Physics]]