Kirchhoff’s Current Law (KCL) with Example: Circuit Analysis

Kirchhoff’s current law KCL state that the total current entering at a node (point in the circuit where multiple components meet) is always the same as the total current leaving out from that node. 

Suppose a node with five component meets, two of them are providing power and the rest of three are consuming power as shown in the diagram. According to KCL, the current provided by those two power sources will be exactly equal to the current consumed by these three power dissipating components.

$\sum{I_{Entering}= \sum{I_{Leaving}}}$

I$_{1}$ + I$_{2}$ = I$_{3}$ + I$_{4}$ + I$_{5}$

Kirchhoff's current law KCL

Note the direction of current in the diagram. The two currents I1 and I2 are entering the node at point P. And three currents are leaving the node.

The KCL holds for DC circuits as well as AC circuits and linear and non-linear components.

Gustav Kirchhoff was a German physicist, who presented two laws. The Kirchhoff’s Current Law (KCL) and Kirchhoff Voltage Law (KVL). Ohm law is a very basic one, which may not be sufficient to analyze a complex circuit. Kirchhoff’s Current Law (KCL) provides the basis for Nodal Voltage Analysis.

Example:

Suppose a node with three wires connected, if one of them is providing a current of 4A and the second is the wire is taking a current of 4A.

What would be the current of the third wire? And what would be the direction of the current?

Solution:

Let’s draw the diagram representing the directions of the current.

Kirchhoff's current Law example

According to the KCL, the entering current will always be equal to leaving current, i.e.

$I_{entering}=I_{leaving}$

The unknown current is entering the node :  

$4A+I=4A$

$I=4A-4A=0A$

The unknown current is zero.

Limitations Of KCL :

Kirchhoff’s Current law assumes that current flows only in conductors, but in the case of high-frequency circuits, current can be caused by parasitic capacitance without any conductor.   

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