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# 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.

Example:

Solve for the value of I3 in figure below. Circuit for example problem.

Solution: First the currents are given proper signs: The currents are placed into the equation with the proper signs as follows:

Basic equation: substitution: combining like terms: Thus, I3 is 2 A and its positive sign shows it to be a current leaving the junction.

Example:

Using figure below, solve for the magnitude and direction of I3. Circuit for example problem.

Solution: Thus, I3 has a value of 2 A, and the negative sign shows it to be a current entering the junction.