Kirchhoff’s current law

Kirchhoff’s current law or nodal rule states that the sums of currents flowing into any node or junction in a circuit will be equal to 0. In others words, the sums of current flowing into the node and out of the node will be equal.

Kirchhoff’s current law example

In this example, the white dot is the node that is going to be analyse. Kirchhoff’s current law speculates that the sums of currents flowing into any node or junction in a circuit will be equal to 0. Arrow going towards the node are going to be positive current and arrow going outwards are going to be negative current. In this specific example, we can find this formula with Kirchhoff’s current law :

I_{1} - I_{2} - I_{3} = 0

We could also write the formula differently. The sums of current flowing into the node and out of the node will be equal. Based on the arrow direction above we get this formula :

I_{1} = I_{2} + I_{3}

The two formulas are based on the orientation of the arrow on the picture. Having the arrow in the incorrect direction is not an issue when you are solving problems using Kirchhoff’s current law. Instead of having a positive value for the current, you will get a negative value for the current which means the arrow direction is incorrect.