# Kirchhoff's Voltage and Current Laws

### Kirchhoff's Current Law

Also called Kirchhoff's first law, Kirchhoff's point rule, Kirchhoff's junction rule (or nodal rule) or Kirchhoff's first rule.

At any junction in an electric circuit** the total current flowing towards the junction or node is equal to the total current flowing away from the junction**.

Kirchhoff's Current Law can be expressed as

Σ I = I_{1}+ I_{2}+ .. + I_{n}= 0 (1)

where

I = currents (amps)

In general - current toward the junction is positive and current flowing away from the junction is negative.

#### Example - Kirchhoff's Current Law

The currents in the figure above is *I _{1} = 0.1 A, I_{2} = 0.2 A, I_{3} = 0.1 A, I_{4} = - 0.05 A, I_{5} = -0.15 A. *

*I _{6} *can be calculated by using Kirchhoff's current law

*(0.1 A) + (0.2 A) + (0.1 A) + (- 0.05 A) + (-0.15 A) + I _{6} = 0 *

*or *

* I _{6} = -((0.1 A) + (0.2 A) + (0.1 A) + (- 0.05 A) + (-0.15 A))*

* = -0.2 A*

### Kirchhoff's Voltage Law

Also called Kirchhoff's second law, Kirchhoff's loop (or mesh) rule, or Kirchhoff's second rule.

In a closed loop in a network **the sum of the voltage drops or potential differences around the loop is zero**.

Kirchhoff's Voltage Law can be expressed as

Σ U = U_{1}+ U_{2}+ .. + U_{n}= 0 (2)

where

U = voltage drop or potential difference (volts)

In a schematic diagram voltage can be measured positive clockwise or anticlockwise.

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