Kirchhoff’s Current Law

Kirchhoff’s Current Law is one of the fundamental laws in Electrical and Electronics Engineering. Also known as KCL, the law explains the behavior of current in parallel circuits.

Statement: The sum of electrical current entering a node is equal to sum of current leaving the node.


Σ Current In = Σ Current Out

Let’s consider a circuit having three resistors:

A current of 10 ampere enters the node (red dote), while a current of 6 A, and 4 A leaves the node.


Σ Current In = Σ Current Out

10 A = 6 A + 4 A

10 A = 10 A

Kirchhoff’s Current Law Solved Example

Question: Find all the unknown currents in the circuit given below.

Solution: First off let’s label all the currents:

Application of KCL at node C yeilds

I3 = 1 A + 2 A

I3 = 3 A

Now application of KCL at node B yeilds

5 A = I2 + I3

5 A = I2 + 3A

I2 = 5 A – 3 A = 2 A

So I2 = 2A

Application of KCL at node A yields

I1 = 5A

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