Difference between revisions 1695549 and 1695550 on enwikiversity

'''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 an Electromagnetic oscillation wave that travels at speed of visible light carries[[Quantum]]'s energy called [[Photon]]

==Electromagnetic radiation spectrum==
: [[File:EM Spectrum Properties edit.svg|thumb|right|2500px]]
==Frequency Bands==
{{main|Radiation astronomy/Bands|Band astronomy}}
The electromagnetic spectrum is divided into several bands.  These definitions are generally informal and vague, and the bands may overlap.  There seems to be a gap between the ultra-violet and X-ray bands.  Sometimes, the choice of band depends on how the radiation is generated.  For example, radiation from radioactive decay is always referred to as gamma rays, even if its photon energy would class it as X-rays.

The main bands used, in order of decreasing wavelength (hence increasing frequency and photon energy) are:

* [[Radio]]
* [[Microwaves]]
* [[Infra-Red]]
* [[Visible light]]
* [[Ultra-violet]]
* [[X-rays]]
* [[Gamma rays]]

A convenient mnemonic for remembering these is "'''R'''abbits '''M'''ate  '''I'''n '''V'''ery '''U'''nusual e'''X'''pensive '''G'''ardens".

There are many bands within these, which are even vaguer and more prone to overlap.  Each band is discussed in more detail below.  The limits given are rough, so exact consistency between wavelength, frequency and photon energy cannot be expected.⏎
⏎
==Units==
{{main|Units}}
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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It follows that a photon with an energy of 1eV has a frequency of 1 eV/h = 2.41799 x 10<sup>14</sup> Hz or about 242 THz and a wavelength of c.h/1 eV = 1.23984 x 10<sup>-6</sup> m or about 1,240nm or 12,400Å.  As will be seen below, that would put the photon in the infrared range.  In practice, photon energies are never quoted for such long wavelengths.

'''Exercise:''' Find why photon energies are only important at very short wavelengths.


==Frequency Bands==
{{main|Radiation astronomy/Bands|Band astronomy}}
The electromagnetic spectrum is divided into several bands.  These definitions are generally informal and vague, and the bands may overlap.  There seems to be a gap between the ultra-violet and X-ray bands.  Sometimes, the choice of band depends on how the radiation is generated.  For example, radiation from radioactive decay is always referred to as gamma rays, even if its photon energy would class it as X-rays.

The main bands used, in order of decreasing wavelength (hence increasing frequency and photon energy) are:

* [[Radio]]
* [[Microwaves]]
* [[Infra-Red]]
* [[Visible light]]
* [[Ultra-violet]]
* [[X-rays]]
* [[Gamma rays]]

A convenient mnemonic for remembering these is "'''R'''abbits '''M'''ate  '''I'''n '''V'''ery '''U'''nusual e'''X'''pensive '''G'''ardens".

There are many bands within these, which are even vaguer and more prone to overlap.  Each band is discussed in more detail below.  The limits given are rough, so exact consistency between wavelength, frequency and photon energy cannot be expected.

==Radio rays==
{{main|Radiation/Radios|Radio radiation|Radios}}
The existence of '''radio waves''' was predicted by James Clerk Maxwell in 1864. Their properties were investigated by Heinrich Hertz (after whom the hertz is named) in 1885-9.

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

==External links==
[[Category:Physics]]
[[Category:Radiation]]
[[Category:Resources last modified in August 2016]]