Basic DC Theory
Kirchhoffs two laws reveal a unique relationship between current, voltage, and
resistance in electrical circuits that is vital to performing and understanding
electrical circuit analysis.
STATE Kirchhoffs voltage law.
STATE Kirchhoffs current law.
Given a circuit, SOLVE problems for voltage and
current using Kirchhoffs laws.
In all of the circuits examined so far, Ohms Law described the relationship between current,
voltage, and resistance. These circuits have been relatively simple in nature. Many circuits are
extremely complex and cannot be solved with Ohms Law. These circuits have many power
sources and branches which would make the use of Ohms Law impractical or impossible.
Through experimentation in 1857 the German physicist Gustav Kirchhoff developed methods to
solve complex circuits. Kirchhoff developed two conclusions, known today as Kirchhoffs Laws.
The sum of the voltage drops around a closed loop is equal to the sum of the
voltage sources of that loop (Kirchhoffs Voltage Law).
The current arriving at any junction point in a circuit is equal to the current
leaving that junction (Kirchhoffs Current Law).
Kirchhoffs two laws may seem obvious based on what we already know about circuit theory.
Even though they may seem very simple, they are powerful tools in solving complex and difficult
Kirchhoffs laws can be related to conservation of energy and charge if we look at a circuit with
one load and source. Since all of the power provided from the source is consumed by the load,
energy and charge are conserved. Since voltage and current can be related to energy and charge,
then Kirchhoffs laws are only restating the laws governing energy and charge conservation.