, being a conservative field, . Since is zero outside the battery and considering finite conductivity only in the conductor region,

......................(3.15)

We define, Electromotive force or EMF to be . In a circuit where we have multiple sources and multiple resistors,

                                                        ..........................................(3.16)

The expression (3.16) is that of Kirchhoff’s voltage Law, which states that algebraic summation of the EMF’s (voltage rise) in a circuit is equal to the algebraic sum of the of the voltage drop across the resistors.