Electrical resistance is the ability of materials to resist the passage of electrical current by itself, when a potential difference is applied to it. By Ohm's law, one can calculate the resistance of a material such as a metallic resistor through of the ratio between the potential difference (V) applied between its terminals and the current (i) that the walks. Mathematically it is:
The unit of resistance in the International System of Units is the ohm, represented by the letter Ω.
Resistors that obey this law are called ohmic resistors, however, this law is only valid for constant temperatures. But there are also materials that are known to increase or decrease electrical resistance as the temperature increases or decreases, these are called variable resistance resistors. For these materials, the equation that determines their strength, with good approximation, is written as follows:
R = RO(1 + αΔt)
Where Δt is the change in material temperature.
The explanation for the variation in the resistance of the metallic resistor as the temperature changes is in the material's internal structure. In the eyes of Modern Physics, two factors determine the electrical resistance of the material: the number of electrons that constitute the material and their mobility within the structure. It is evident that the greater the number of free electrons, the lower the electrical resistance. The resistance will also be smaller the easier it is for the electrons to move within the crystalline lattice that constitutes the material.
By Marco Aurélio da Silva
Brazil School Team
Electricity - Physics - Brazil School
Source: Brazil School - https://brasilescola.uol.com.br/fisica/resistencia-constante-ou-resistencia-variavel.htm
