By the 1850s, the wave model of light was widely accepted. But there was a problem: if light is a wave, how does it travel through the vacuum between the Sun and the Earth? Some people proposed a luminiferous ether—a medium permeating all of space that allows light to get around. This concept was disproved by an experiment by Michelson and Morley.
In the early 1860s, Maxwell developed four equations to relative electric and magnetic fields. These equations said that a changing electric field produces a magnetic field, and vice versa. The fields are perpendicular to each other, and they interact to produce a self-propagating electromagnetic wave. The speed of this hypothetical wave turned out to be the same as the speed of light! What’s more, a self-propagating wave doesn’t need a medium to travel through, so this solved the problem of the vacuum.
In 1887, Hertz observed all the predicated wave properties for Maxwell’s equations. In particular, electromagnetic waves
We now know quite a bit about the electromagnetic spectrum. Here are its different regions in increasing order of frequency (decreasing order of wavelength):
|Band||From (Hz)||To (Hz)|
|visible||4 × 1014||8 × 1014|
|ultraviolet||8 × 1014||1017|