Kirchhoff's Current Law (KCL)

Introduction
Kirchhoff's Current Law (KCL) is a fundamental law in electrical engineering that states that the sum of currents entering a node (or junction) in an electrical circuit is equal to the sum of currents leaving that node. KCL is based on the principle of conservation of charge, which states that charge is neither created nor destroyed in an electrical circuit.

KCL Application
KCL is applied at nodes in an electrical circuit. A node is a point in a circuit where two or more circuit elements are connected. It can be a junction between two or more wires, a connection between components, or a point where current splits or merges.

Explanation
When KCL is applied at a node, it involves writing an equation that represents the sum of currents entering the node and the sum of currents leaving the node. The equation is based on the principle that the total charge entering the node must be equal to the total charge leaving the node.

To apply KCL at a node:
1. Identify the node where KCL needs to be applied.
2. Assign a reference direction for currents entering and leaving the node. Typically, incoming currents are considered positive, and outgoing currents are considered negative.
3. Write an equation based on the sum of currents entering and leaving the node, considering the reference directions. The equation will be of the form:
∑(incoming currents) = ∑(outgoing currents)
4. Solve the equation to determine the unknown currents or variables.

Example
Consider a simple circuit with three resistors connected to a node. Let's assume that the currents entering the node are I1 and I2, and the current leaving the node is I3. Applying KCL at the node, the equation would be:
I1 + I2 = I3

Conclusion
Kirchhoff's Current Law (KCL) is applied at nodes in an electrical circuit. It is based on the principle of conservation of charge and states that the sum of currents entering a node is equal to the sum of currents leaving that node. KCL is a fundamental tool in circuit analysis and is used to solve complex electrical circuits.