Section

The electric current is a continuous movement of elementary electric charges, a flow of electrons, which takes place inside some materials. The materials that allow free electrons to move from one atom to another thus permitting the current to cross them are called conductors. Insulators instead are materials through which the electric charge is transferred with extreme difficulty.

The intensity of the current is the ratio between the amount of charge q passing in a section of the conductor and the time interval in which it passes; the current is measured in ampere (A).

i = q / Δt

In the presence of an ohmic conductor, the electric current meets a resistance (R), measured in Ohms, which depends on the potential difference (V), measured in Volts, and on the current (i) according to the following relation

R = V / i

the electrical resistance can be expressed as

R = ρ l / S

The electrical resistivity ρ is an intrinsic physical property of any material and indicates the predisposition of a material to resist the passage of electric charges. It is measured in Ωm