1.8: Kirchhoff's Current Law
In the realm of electrical engineering, physicist Gustav Robert Kirchhoff made a significant contribution in 1847 by introducing Kirchhoff's laws for electric circuit analysis. These laws, particularly Kirchhoff's Current Law (KCL), have become foundational principles in understanding and analyzing electrical circuits.
Kirchhoff's Current Law is based on the principle of charge conservation. It states that at any node (a point where two or more circuit elements meet) in an electrical circuit, the total current entering the node is equal to the total current leaving the node. This means that no current is lost at the junction, reflecting the fundamental principle that electric charge is conserved.
In the application of KCL, currents leaving the node are assigned a negative sign, while currents entering the node are given a positive sign. By algebraically summing these currents at a node and integrating them over time, one can determine the total electric charge at the node.
According to the law of charge conservation, the net electric charge at any node remains constant over time, ensuring that the node stores no net charge. Therefore, if the net charge at a node is zero, the total current entering and leaving that node must also be zero. This validates the application of KCL in circuit analysis.
Interestingly, KCL can also be generalized for a closed boundary by conceptualizing a node as a closed surface condensed to a point. This allows for the application of KCL in more complex circuit environments.
KCL is also useful in determining the combined current from parallel current sources. By algebraically summing the individual currents at a node, the total current through that node can be found.
However, for KCL to hold true, a critical condition must be met: a circuit cannot have two unequal currents in series. This is because, in a series connection, the same current flows through all components, and any discrepancy would violate the law of charge conservation.
