Physics / Ohm Laws

Ohm Laws

The Ohm Laws , postulated by German physicist Georg Simon Ohm (1787-1854) in 1827, determine the electrical resistance of conductors.

In addition to defining the concept of electrical resistance, Georg Ohm demonstrated that in the conductor the electric current is directly proportional to the applied potential difference.

This is how he postulated Ohm's First Law .

His experiments with different lengths and thicknesses of electrical wires were crucial in postulating Ohm's Second Law .

In it, the electrical resistance of the conductor, depending on the material's constitution, is proportional to its length. At the same time, it is inversely proportional to its cross-sectional area.

Electrical resistance

Electrical resistance , measured under the magnitude Ω ( Ohm ), means the ability of a conductor to oppose the passage of electrical current.

In other words, the function of electrical resistance is to make it difficult for electric current to pass through.

Note that 1 resistência (ohm) resistance equals 1V / A (Volts / Ampere)


Resistors are electronic devices whose function is to transform electrical energy into thermal energy (heat) through the joule effect .

Thus, ohmic or linear resistors are those that obey the first ohm law (R = U / I). The intensity (i) of the electric current is directly proportional to its potential difference (ddp), also called voltage. On the other hand, non-ohmic resistors do not obey the ohm law.

Ohm's Laws: Statements and Formulas

Ohm's First Law

Ohm's First Law postulates that an ohmic conductor (constant resistance) maintained at constant temperature, the intensity (i) of electric current will be proportional to the potential difference (ddp) applied between its ends.

That is, its electrical resistance is constant . It is represented by the following formula:


At where:

R : resistance, measured in Ohm (Ω)
U : electric potential difference (ddp), measured in Volts (V)
I : intensity of electric current, measured in Ampere (A).

Ohm's Second Law

Ohm's Second Law states that the electrical resistance of a material is directly proportional to its length, inversely proportional to its cross-sectional area.

Moreover, it depends on the material of which it is constituted.

It is represented by the following formula:

At where:

R : resistance (Ω)
ρ : conductor resistivity (depends on material and temperature, measured in Ω.m)
L : length (m)
A : cross-sectional area (mm 2 )