Kirchhoff's Laws: The Basics

Kirchhoff's Laws: The Basics

Since current is the flow of electrons through a conductor, it cannot build up at a junction, meaning that current is conserved: What goes in must come out. You can think of perhaps the most well-known example of a junction: a junction box. These boxes are installed on most houses: They are the boxes that contain the wiring through which all electricity in the home must flow

when performing calculations, then, the current flowing into and out of the junction typically has opposite signs. You can also state Kirchhoff's Current Law as:

Kirchhoff's Current Law

In the picture, a junction of four conductors (wires) is shown. The currents i₂ and i₃ are flowing into the junction, while i₁ and i₄ flow out of it. In this example, Kirchhoff's Junction Rule yields the following equation  

[i ₂ + i ₃ = i ₁ + i _4]

Kirchhoff's Voltage Law

Kirchhoff's Voltage Law describes the distribution of electrical voltage within a loop, or closed conducting path, of an electrical circuit. Specifically, Kirchhoff's Voltage Law states. 

The directed sum of the potential deference (voltages) around any closed loop is zero

Positive and Negative Signs in Kirchhoff's Voltage Law

You choose a direction (clockwise or counterclockwise) to go along the loop. 

When traveling from positive to negative (+ to -) in an emf (power source) the voltage drops, so the value is negative. When going from negative to positive (- to +) the voltage goes up, so the value is positive.

Remember that when traveling around the circuit to apply Kirchhoff's Voltage Law, be sure you are always going in the same direction (clockwise or counterclockwise) to determine whether a given element represents an increase or decrease in the voltage. If you begin jumping around, moving in different directions, your equation will be incorrect.

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