The English physicist and physician Thomas Young (1773-1829) did his experiments on the nature of light believing that it, like sound, spread in waves.
However, it was the French physicist and engineer Augustin Fresnel (1788-1827) who demonstrated this fact.
We have already seen that the waves can be mechanical or electromagnetic. Electromagnetic waves differ in frequency. Therefore we can arrange them in an orderly sequence in the increasing direction of frequencies. This sequence is called electromagnetic spectrum.
In the electromagnetic spectrum, the farther we go to the right, the higher the frequency and the shorter the wavelength.
Each region of this spectrum corresponds to waves that have a certain frequency range and have different applications. Light waves, for example, occupy a certain region of this spectrum.
Since frequency and wavelength are inversely proportional quantities, we can present the same electromagnetic spectrum indicating the increasing direction of frequencies and the decreasing direction of wavelengths. The medium considered is vacuum, where the speed of light is 300 000 km / s.
As we have seen, when these waves propagate in a vacuum, they propagate at a speed of 300,000 km / s. According to the Relativity Theoryby Einstein, this is the highest speed that can be reached in nature.
The velocities of electromagnetic waves in other media will have a value distinct from their vacuum value, and always lower than it.