Simply, Kirchhoff’s Laws
What does it take to understand the most simple straightforward laws that allows you to analyze a simple electric circuit?
The answer is **drum rolls** one article! Yes one single article is “enough” to understand and appreciate these laws. Far away from the complexity of the books and the low quality of the videos …
In this article, I will be trying to deliver a direct approach to understand the famous Kirchhoff’s laws, and how they can be used interchangeably with Ohm’s law to analyze any electric circuit.
In 1874, a German physicist named Gustav Robert Kirchhoff stated two basic laws which became essential laws when it comes to circuit analysis.
The Kirchhoff’s laws and Ohm’s law has formed the basis of circuit theory which enables electric engineers to determine the characteristics and the behavior of basic electrical circuits.
Kirchhoff’s Current Law (KCL)
Kirchhoff’s current law is essentially based on the law of conservation of charge, which requires that the algebraic sum of charges within a system cannot be changes.
Definition: The algebraic sum of currents entering a node is zero.
What does that mean?
Basically, it means that when you examine a node in an electric circuit, the current that enters the node will leave the node!
Let’s us apply KCL analysis at the below figure of currents at nod …
You can notice that the currents entering the node are considered as Positive (+) and the currents leaving the node are Negative (-)
Once you obtain the simplified version of the KCL equation, we can state that the sum of the currents on the left-side of the equation is equal to the sum of currents on the right-side of the equation.
Kirchhoff’s Voltage Law (KVL)
Kirchhoff’s voltage law is essentially based on the law of conservation of energy, which requires that the algebraic sum of all voltages around a closed loop is zero.
Definition: The algebraic sum of all voltages around a closed path (loop) is zero.
What does that mean?
Basically, it means that when you are going around a circuit and you sum the voltages with the proper sign you sum will eventually be equal to zero!
Let us apply KVL analysis at the below figure of voltages …
Notice that the sign on each voltage is the polarity of the terminal encountered first as you go around the loop.
Combining Kirchhoff’s laws with Ohm’s law
Example #1:
Let us apply Ohm’s law to find the voltages’ value
then we apply KVL to determine the current …
Now, we use the current value to evaluate and find the unknown voltage values …
With the combination of Ohm’s law and Kirchhoff’s voltage law (KVL), we were able to determine the value of the unknown voltages in the simple electric circuit above.
