Electrical charges in motion produce emission of electromagnetic
waves, like radio waves we use for cell phones and radio programs,
millimeter waves we use in radars, visible light, X-rays and gamma
rays.
All the above forms of electromagnetic radiation differs from
their frequency, in particular I have listed them in order of
increasing frequency (and decreasing wavelength).
When a real wave is emitted a set of frequencies are emitted,
almost never a single frequency. Under a fundamental point of view
this is due to the quantum mechanical indetermination principle. In
practical cases, quite more important causes are the fluctuations
in the speed of moving charges and the fact that their trajectory
is not purely linear.
The set of frequencies that forms a practical wave is called
electromagnetic spectrum of that wave.
The overall frequency axes is divided in zone, as listed
below
Region
Wavelength (Angstroms)
Wavelength (centimeters)
Frequency (Hz)
Energy (eV)
Radio
> 109
> 10
< 3 x 109
< 10-5
Microwave
109 - 106
10 - 0.01
3 x 109 - 3 x 1012
10-5 - 0.01
Infrared
106 - 7000
0.01 - 7 x 10-5
3 x 1012 - 4.3 x 1014
0.01 - 2
Visible
7000 - 4000
7 x 10-5 - 4 x 10-5
4.3 x 1014 - 7.5 x 1014
2 - 3
Ultraviolet
4000 - 10
4 x 10-5 - 10-7
7.5 x 1014 - 3 x 1017
3 - 103
X-Rays
10 - 0.1
10-7 - 10-9
3 x 1017 - 3 x 1019
103 - 105
Gamma Rays
< 0.1
< 10-9
> 3 x 1019
> 105
Sub-zones are also defined.
Since the energy of a photon of an electromagnetic wave at a
certain frequency f is proportional to the frequency by the
equation
Energy= h f
where h is the Plank constant, higher the frequency, higher the
phonons energy as indicated in the table (the energy of one
electronvolt eV is the energy aquired by an electron when
accelerated by a potential of one volt and it is equal to 1.6×10−19
joule).
