# Kirchhoff’s Law

What is commonly referred to as Kirchhoff’s law is a set of 2 laws that govern electrical circuits. Kirchhoff’s current rule and Kirchhoff’s voltage law are collectively known as Kirchhoff’s law for easy reference in layman terms. Kirchoff’s laws are generally applied to DC circuits, but they can be applied to AC circuits at frequencies where the wavelength of EM radiation is very large in comparison with the circuits. That being said, let’s take a deep dive into what Kirchhoff’s first law and second law say.

## Kirchhoff’s First Law

Kirchhoff’s first rule also called Kirchhoff’s current rule, Kirchhoff’s junction rule, Kirchhoff’s point rule, or Kirchhoff’s nodal rule, states that, for any node or junction in an electrical circuit, the sum of currents flowing into the node is equal to the sum of currents flowing out of that node. In other words, the algebraic sum of all the currents in a network of conductors meeting at a single point will be equal to zero.

### Uses

Kirchhoff’s current rule has several important applications in electrical engineering.

• It is used in combination with Ohm’s law to perform nodal analysis of electrical circuits.
• A matrix version of the current law is used as the basis of the creation of circuit simulation software like SPICE.
• It can be applied to lumped networks regardless of the nature of the network.

## Kirchhoff’s Second Law

Kirchhoff’s second rule also called Kirchhoff’s voltage principle, Kirchhoff’s loop rule, or Kirchhoff’s mesh rule, states that the voltage drop across any selected loop is zero if it is within the low-frequency limit.

### Uses

• Helps determine the unknown sources such as voltage and current with mesh equations
• Simplifies complex electrical circuits
• Reduces the amount of math required to solve the circuit
• Analysis of complex circuits or networks
• Practical applications in problems that are related to static electricity