If we have several sections of an electrical circuit, which would have to go obtaining equivalent resistance of each section, would complicate the analysis of Ohm's law. For such cases we use the electric circuit analysis by the law of Kirchhoff's voltage and current.
-Kirchhoff's law of voltages: the sum of the voltages in a closed mesh equals zero. That is:
Where E is summation, and n is the corresponding value for each element of the mesh. -Kirchhoff's Current Law: The sum of the currents entering a node equals the sum of the currents leaving. That is
Let's look first by Kirchhoff's Current Law. The LCK tells us that the currents entering a node are equal to the sum of the currents leaving.In this circuit, specifically in R1, there are two nodes, the node above which we will call A and the node below which we will call B.
To solve the circuit can be considered only one node, in this case we will choose the node A. Node A is affected by three currents are those of R2, R1 and R3. So we can say that:
Then, we say that enters a current I1 to node A and leaving two currents I2 and I3, so I1 = I2 + I3.The real meaning of the currents depend on the value obtained at the end of each. If the currents are negative, then the flow of them, if they come, would actually be leaving, and if they leave, it would be coming, that is the opposite of the original analysis.