All of us are surrounded by a huge number of a wide variety of devices and entire systems based on them, which in the course of their functioning in one way or another consume electric current. The very concept of electric current was introduced in order to give the description of the process of its course a certain clarity, which was achieved due to the purposeful formation of a direct analogy with hydrodynamics through fluid flow.
With the accumulation of knowledge about electricity, it was shown that the flow of electric current is primarily movement of an electromagnetic field along a conductive medium that occurs at speeds not too different from speed Sveta. In this case, the field moves from a point with a higher potential in the direction of a point with a lower potential, i.e. according to the classic scheme from plus to minus.
The movement of charge carriers proper, which accompanies this process, also takes place, but at a noticeably lower speed. In different materials, it takes place in different directions.
Varieties of charge carriers
It is known that charge carriers are divided into positive and negative ones. Negative charges are possessed by electrons and ions, ions prevail among carriers of a positive charge. Negative charges move towards higher potential, while positive charges move towards lower potential. And in both cases, an electric current occurs in the environment.
A classic ambiguity appears, which is eliminated by conventional agreement. At the postulate level, it is assumed that the current always flows from plus to minus, regardless of the type of charges.
The movement of charges in metals
Most metals at temperatures that are practically important for electrical and wire communication technology are in a solid state and there are no ions in them.
As a result, the current in solid conducting materials is determined by the electronic type of conductivity, i.e. free electrons (Figure 1), which take on the functions of charge carriers, in the process of current flow, they move in the direction opposite to the direction of current flow, picture 2.
Electrons in metals are easily torn off by an electric field from their orbits, along which they rotate around atoms in the absence of a potential difference. Thus, with an insignificant potential difference, a large number of charge carriers are formed, i.e. metals have relatively low electrical resistance.
The movement of charges in semiconductors
Semiconductors are noticeably inferior to metals in conductivity at room temperature. Materials belonging to this group are divided into n-type and p-type semiconductors. Semiconductors of the n-type in the normal state have an excess of electrons, when passing to the p-type, it manifests itself lack of electrons, but the remaining relatively easily move from one allowed position in atoms to another. The latter is equivalent to the movement of positive charges.
A feature of semiconductors is that their conductivity increases sharply as the temperature rises: due to the weak bond with atoms, as it rises, the number of unbound electrons changes significantly.
Thus, the direction of movement of charges in semiconductors can either coincide with the direction of current flow (p-type), or be opposite to it (n-type).
The movement of charges in liquids and gases
A feature of liquids and gases is that ions are charge carriers in them. They can be either positive (cations) or negative (anions), Figure 3. Accordingly, when negative cations predominate, they move “against the current”, while positive cations move “along the current”.