Kirchhoff's Current Law
Kirchhoff's Current Law states:
The algebraic sum of the currents entering and leaving any junction of conductors is equal to zero.
This law can be stated mathematically as:
where: I1, I2, etc., are the currents entering and leaving the junction. Currents entering the junction are considered to be negative and currents leaving the junction are considered to be positive. When solving a problem using Kirchhoff’s current law, the currents must be placed into the equation with the proper polarity signs attached.
Solve for the value of I3 in figure below.
Solution: First the currents are given proper signs:
The currents are placed into the equation with the proper signs as follows:
combining like terms:
Thus, I3 is 2 A and its positive sign shows it to be a current leaving the junction.
Using figure below, solve for the magnitude and direction of I3.
Thus, I3 has a value of 2 A, and the negative sign shows it to be a current entering the junction.