In today’s world it is almost impossible to live without electricity. If we look around us, we will see several pieces of equipment that need electricity to function. When we refer to the study of electricity, we are actually referring to the phenomena resulting from the property called electric charge .
Thinking about historical facts, we see that several hypotheses and several theories were raised and developed in order to give more concise explanations about electrical phenomena. Today we know with full conviction that such phenomena are linked to the structure of matter.
As we have already studied, we know that all bodies are made up of atoms, which can be described as made up of elementary particles. The main ones are protons, neutrons and electrons.
Electric charge is a property that is closely associated with certain elementary particles that make up the atom ( protons and electrons ). The planetary system model is the most adopted simple model to explain how such particles are distributed in the atom. According to the planetary model, the protons and neutrons are located in the nucleus, whereas the electrons are in a region called the electrosphere.
Through experiments it was possible to show that protons and electrons have opposite electrical behaviors. Therefore, it was agreed that there are two kinds of electric charges: the positive one, which behaves like a proton; and the negative, which behaves like the electrical charge of the neutron. Neutrons do not have the aforementioned physical property, that is, neutrons do not have an electrical charge.
In the International System of Units (SI), the unit of electric charge is the coulomb ( C ). The proton and electron, in magnitude, have the same amount of electric charge. The value of the charge on the proton and electron is called the amount of elementary charge ( e ) and has the value of:
As 1 C is a very large amount of electric charge, it is common to use its submultiples:
1 mC ( milicoulomb ) = 10 -3 C
1 μC ( microcoulomb ) = 10 -6 C
1 nC ( nanocoulomb ) = 10 -9 C
The amount of total electrical charge (Q) will always be an integer multiple (n) times the value of the elementary charge (e). This amount of charge can be determined through the following expression:
Generally, when any body has the same number of protons as the number of electrons, we say that this body is electrically neutral, that is, the body has a total charge equal to zero. Therefore, when the body has a number of protons different from the number of electrons, we say that the body is electrified, that is, the body has a non-zero electric charge.
In all experiments carried out so far, it appears that, in isolated systems, the amount of electrical charge remains constant. This law is called conservation of the amount of electric charge. Therefore, we can say that electric charge is not created and is not lost, it is just transferred from one body to another.