Difference between revisions 920459 and 928614 on enwikiversity

[[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.

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'''UVA, UVB, UVC''' are terms used to assess how dangerous the UV is to human skin.

* '''UVA''': 320-400 nm: Not absorbed by ozone layer; fairly harmless		
* '''UVB''': 280-320 nm: Partly absorbed by ozone layer; more dangerous		
* '''UVC''': 100-280 nm: Totally absorbed by ozone layer; most dangerous


Short-wave UV, X-ray and gmma-ray radiation are sometimes lumped together as '''ionising radiation''', because the photons are energetic enough to knock electrons out of atoms, ionising them.  Such radiation is dangerous to living things, because the ionisation can disrupt biochemical processes and even cause cancer.  Alpha and beta particles can also be called ionising radiation.⏎
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== X-rays ==
These have a wavelength of 0.01 to 10 nm, hence photon energies of 1keV to 1000keV.  They were discovered by Wilhelm Roentgen in 1895.

Often, X-rays are divided into '''hard X-rays''' (wavelength of 0.01 to 0.1 nm, photon energies of 10keV to 1000keV) and '''soft X-rays''' (wavelength of 0.1 to 10 nm, photon energies of 0.1keV to 10keV).  In general, shorter wavelength X-rays are said to be harder than longer wavelength ones.

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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]]