The ohm's law of the whole circuit generally refers to the ohm's law of the closed circuit. The current of the closed circuit is directly proportional to the electromotive force of the power supply and inversely proportional to the sum of the resistances of the internal and external circuits. The formula is I=E/(R+r), I represents the current in the circuit, E represents the electromotive force, R represents the external total resistance, and R represents the internal resistance of the battery. Commonly used variants are E = I (R+R); E = outer u+ inner u; U external =E-Ir.

Its change law obeys ohm's law of active circuit, and its mathematical expression is: u = e-IR.

Where U is the terminal voltage and Ir is the internal voltage of the power supply, also called internal voltage drop. For a given power supply, both electromotive force e and internal resistance r are certain. As can be seen from the above formula, the terminal voltage u of the circuit is related to the current in the circuit. When the current I increases, the internal pressure drop Ir increases and the terminal voltage U decreases. On the contrary, when the current I decreases, the terminal voltage u increases.

The application scope of ohm's law of the whole circuit: pure resistance circuit, energy conversion in closed circuit;

E=U+Ir，ei =UI+I 2r，pRelease = EI，pOutput = ui。

In a pure resistance circuit

P output = I 2r = e 2r/(r+r) 2 = e 2/(r 2+2r+r 2/r), when r=R, p output is the largest, and p output = e 2/4r (mean inequality).