What is ohm’s law and how is it used?

What is ohm’s law?

Ohm’s law is a law that explains the behavior of electricity through three important concepts. As are the current, voltage and electrical resistance. This law was proposed by physicist and mathematician Georg Simon Ohm, the symbol by which he is known is Ω and is known as one of the fundamental laws for electricity and electronics.

ohm's law


What does this law declare?

Ohm’s law says that the current flowing through an electrical conductor is directly proportional to the applied voltage and inversely proportional to the resistance. Despite the complexity of the explanation, it is very simple to understand using the formula and dividing it into parts.

Formula V = I * R where:

  • V: is the voltage
  • I: is the electric current
  • R: electrical resistance


If we clear the formula we may be able to know the value of any of these three elements before having the armed circuit in our hands and we can also understand it better

I = V / R

The current is directly proportional to the voltage and inversely proportional to the electrical resistance.


V = I * R

To calculate the voltage we have to multiply the current by the resistance.

R = V / I

To calculate the resistance of a circuit we have to divide the voltage by the current.

Ohm’s law applications

The applications of this law are practically unlimited since it deals with any circuit that requires electricity to operate. The most common example is a circuit with a resistor and a voltage power supply. Although on many occasions we will have much more complex circuits it is only a matter of simplifying it until we find the total resistance of the circuit to make it easier to calculate. (next article circuit simplification)

Extreme conditions in ohm’s law

There are 2 possible unusual conditions within this law, which are considered with negative effects to the circuits, these conditions are:

  • Short circuit: This is probably the most destructive since all electrical components have a certain current tolerance range. When a short circuit occurs the current is equal to the voltage and this ends up burning the components since they have a lower range of acceptance to the current than to the voltage. A short circuit can also a spark that can be deadly.
  • Open circuit: This condition is not destructive since the resistance has infinity and as the law of ohm explains that the higher the resistance, the lower the current. The circuit is not able to conduct electrical current.


Ohm’s law and power

There is a more complete way to calculate the electrical circuits in their entirety, since in some situations they have parts of the information but not the complete data, sometimes you only have the current and the total resistance but you don’t know the voltage, with ohm’s law, just use a formula to know the value of this mystery.

But what if at some point I want to know the voltage and I only have the current data and not the resistance data? There is one more possibility to know the voltage as long as there is extra data that is the power V = P / I.

ohm formula chart

As we can see in the previous image, just by adding the unit of power to the ohm law, it becomes more effective because of the possibilities of calculating the electrical and / or electronic circuits increase.