In physics, the description of the properties of light generally refers to its wavelength (nm), while in the range of microwaves and radio waves we refer to the frequency of a signal (e.g. kHz or MHz). Why is that so?
This is just history, and how things are measured. It is also not true that microwaves are only referred to by frequency. They are called centimetre waves, and 100 GHz is referred to as mm wave. Even at low frequency, am radio at 200 kHz was known as long wave, and we looked for it at 1500 metres. Above that was short-wave! At low frequencies it is easier to measure the time of a period, or how many periods there are in a second. With light it is easier to measure the wavelength using diffraction by a grating (which has its line spacing measured in microns, or lines per cm), with a formula that relates angle to wavelength and grating period.
I am learning to think in both, because I am a microwave man, but am now working in near infra red, so am just learning what that is in frequency, but as I type this I find I still have to work it out and don't know wavelength and frequency instinctively yet, as I do from 1 GHz to 300 GHz.
As the frequency of light is beyond 100 Thz, which is unquantizable and unimaginable. Wavelength is inversely proportional to the frequency of operation therefore, to lowers its limit and to improve its physical interpretations, light is presented in terms of the wavelength (400 nm to 700 nm).
Dear Immo Trinks ,
I think Malcolm White and Sovan Mohanty are right.
It is due to history and mainly on how to measure their properties (either by wave length or frequency) and but also on their applications. Especially light with respect to interferometry and diffraction more relates to distances and thus these effects are easily coupled to and are described by its wavelength; even down to x-rays in the wave length regime of nm or A (Angström).
But let me extend the content of your question from the microwave, optical and UV regime to VUV and x-rays as well as to gamma rays;
for much lower wavelengths than the optical regime, the photon energy in units of eV, keV or even in MeV is used instead of wave length and frequency. Here the energy, which is associated with the photons, is of main interest; so for example in the areas of excitation of molecular and atomic energy levels up to pair production, which are commonly described by energies and not by wavelengths and frequencies.
That is due to the properties of the photon, which can be decribed either by the frecuency, the wavelength or the photon energy.
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