The mathematical expression of ohm's law is: I = u/R. According to this formula, there are two variants: R=U/I and U=IR.
It should be noted that the variable R=U/I means that when the current in the conductor is constant, the voltage across the conductor is proportional to the resistance of the conductor; When the voltage across the conductor is constant, the current is inversely proportional to the resistance. The magnitude of conductor resistance has nothing to do with the voltage across the conductor and the current passing through the conductor, but is determined by the material, thickness and length of the conductor.
Application and limitation of ohm's law
In physics, ohm's law can express the relationship between voltage and current in a macroscopic way, that is, the relationship between the voltage at both ends of circuit elements and the current passing through them; Ohm's law will also be used to study the micro-electrical properties of matter.
Ohm's law is also applicable to electrolyte (aqueous solution of acid, alkali and salt) plasma conductors when the temperature or temperature change range is not too large. However, under the condition of gas ionization, ohm's law does not hold true for the conductive state and some conductive devices (such as electron tubes and transistors).