# Wavelength and Frequencies

The radiation we know best is the visible light that covers a range of wavelengths from 380 to 780 nm (nm = nanometer, 10-9 m) and spreads with the so-called speed of light abbreviated by c.The light of the sun and of every bulb is also an electromagnetic wave.

Another kind of electromagnetic radiation, which is important in our daily life, are the "radio waves" to receive broadcasts or mobile calls or at the doctor's who X-rays our body with a high-energy radiation. The only property that distinguishes these electromagnetic waves in the examples is their wavelength λ and the corresponding frequency ν. Further in the micro world, there are also "exotic" waves, like particle waves, as an example for matter the neutron waves, which are used in fundamental research and in applied sciences. Nuclear research reactors deliver neutron waves within a large energy range.

There is only one difference between these examples of radiation: the frequency of the waves, and consequently their wavelengths. As we know from the Planck's equation, the frequency of a wave is uniquely corresponding to its energy:

E = h × ν          and          ν = c / λ

An illustration on the next page gives an overview over the different wavelengths λ, which we have to deal with in the everyday life; the whole range of values, the spectrum is very broad. To summarize it in just one figure we choose a logarithmic representation (every gradation mark to the right or to the left means an increase or a reduction by the factor of 10).

Spectrum