Kirchhoff Laws

Kirchhoff’s Circuit Law

In 1845, a German physicist, Gustav Kirchhoff developed a pair or set of rules or laws which deal with the conservation of current and energy within electrical circuits.

Both the rules known as: Kirchhoff’s Circuit Laws 

with one of Kirchhoff’s laws deal with the current flowing around a close circuit Kirchhoff’s Current Law, (KCL) 

while the other law deals with the voltage sources present in a closed circuit, Kirchhoff’s Voltage Law, (KVL).

Kirchhoffs Circuit Laws allow us to solve complex circuit problems by defining a set of basic network laws and theorems for the voltages and currents around a circuit.

Kirchhoff's Circuit

1:Kirchhoff’s Current Law, (KCL)

Kirchhoff’s Current Law or KCL, states that the “total current or charge enter in a junction or node is exactly equal to the charge leaving the node. As it has no other place to go except to leave moreover no charge lost within the node“.

In other words the algebraic sum of ALL the currents entering and leaving a node must be equal to zero, I(exiting) + I(entering) = 0. This idea becomes the Conservation of Charge.

1: Kirchhoff’s Current Law:

kirchhoffs current law

Here, the three currents entering the node, I1, I2, I3.All are positive in value and the two currents leaving the node, I4 and I5 are negative in value. Then this means we can also rewrite the equation as;

I1 + I2 + I3 – I4 – I5 = 0

Also for current to flow either in or out of a node a closed circuit path must exist. We can use Kirchhoff’s current law when analysing parallel circuits.

2:Kirchhoff’s Voltage Law, (KVL)

Kirchhoff’s Voltage Law or KVL, states that “in any closed loop network, the total voltage around the loop is equal to the sum of all the voltage drops within the same loop” which is also equal to zero. In other words the algebraic sum of all voltages within the loop must be equal to zero. This Phenomena becomes the Conservation of Energy.

2: Kirchhoffs Voltage Law 

Starting at any point in the loop continue in the same direction noting the direction of all the voltage drops, either positive or negative, and returning back to the same starting point.

It is important to maintain the same direction either clockwise or anti-clockwise or the final voltage sum will not be equal to zero. We can use Kirchhoff’s voltage law when analyzing series circuits.

When analyzing either DC circuits or AC circuits using Kirchhoff’s Circuit Laws. A number of definition and terminologies are use to describe the parts of the circuit analyze.

such as node, paths, branches, loops and meshes.

These terms are used frequently in circuit analysis so it is important to understand them.

Common Terms;

  1. • Circuit A closed loop conducting path in which an electrical current flows.
  2. • Path: connecting elements or sources by single Line.
  3. • Node is a junction within a circuit were two or more circuit elements are connected together. Provide a connection point between two or more branches. A node is indicated by a dot.
  4. • Branch is a single or group of components which are connected between two nodes. such as resistors or a source.
  5. • Loop is a simple closed path in a circuit in which no circuit element or node is encountered more than once.
  6. • Mesh it is a closed loop series path that does not contain any other paths. There are no loops inside a mesh.
Example: Calculate the unknown currents in the following circuits.

Example: Kirchhoffs Voltage Law, (KVL)


2 Comments to “Kirchhoff’s Circuit Law”

  1. I love the way you explain

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