The basic function of a resistor is the dissipation of electromagnetic energy. In an electric circuit, the electric current consist in, to set in motion the charged particles of a conductor; from the electric energy supplied by a source. In the case of metallic conductors, the current is the movement of electrons through the crystal lattice of conductive material; during its motion, the electrons collide with the lattice ions and dissipate the energy supplied by the source(voltage), causing a decrease in the value of the current intensity and the heating of the conductor.
Ohm's law expresses this function of the resistance in a circuit:
I = V/R
The current intensity I, which represents the movement of electrons is directly proportional to the potential V, which represents the electromagnetic energy and is inversely proportional to resistance R, which represents collisions of electrons with the crystal lattice of the material.
In the electric and electronic circuits, the resistors, are used to cause heating when necessary; also they can be used as voltage dividers, that is, to divide a given voltage value, in lower values, in addition to other applications.