Plasma, also known as the fourth physical state of matter, is formed by a mass of ionized gas at very high temperature.
It is common in our daily lives to find substances in their three physical states : solid, liquid or gas. Although it is not easy to obtain plasma on the surface of our planet, it constitutes 99% of everything that exists in the universe. This is because most of the celestial bodies are formed by substances in this state of aggregation. Although rare, we can cite some examples of the presence of plasma, such as fire, fluorescent lamps, plasma screen television, lightning , among others.
To better understand how plasma is formed, let’s take the case of water as an example. When we supply energy (heat) to the ice, it melts and turns into water. When providing energy to water, it evaporates and turns into steam. If we supply even more energy to the steam, the molecular thermal agitation will be greater than the binding forces that keep the electrons in orbit and ionization of the gases (oxygen and hydrogen) will occur, which will make the substance become electrically conductive. and hot.
The following figure shows the four physical states of matter:
Gases and plasma have some characteristics in common, such as low density and the ability to flow. Despite this, they cannot be classified equally, since, at the atomic and molecular level, they have completely different structures and properties. Plasma can conduct electrical current better than copper, flow like a viscous liquid, and interact with electric and magnetic fields unlike gases.
Although plasma is a good conductor of electricity, one of its most important characteristics is its tendency to remain electrically neutral, as it has the same amount of negative and positive electrical charges. The interaction between these charges is responsible for the aforementioned properties.
In addition, plasma always emits light when it comes into contact with some electrical excitation and magnetic fields. An example of this is the polar auroras , which form from the interaction between charged solar particles and the Earth’s magnetic field.
The first scientist to describe plasma was the English physicist William Crookes (1932-1919), in the 1850s, after the creation of the cathode ray tube. This consists of a glass tube filled with low-pressure gases that, when subjected to a potential difference, become conductors.
When a gas conducts electricity, you can observe the formation of small rays, which are called cathode rays. They have the property of emitting light when they collide with the glass walls of the tube, generating plasma.
A few years later, it was JJ Thompson who discovered the electron through the cathode ray tube. It was not until 1928 that Irving Langmuir gave these rays the name plasma because the shape of the electrical fluid obtained resembled blood plasma.