Ohm's law

Ohm's law is a physical law that relates, in an electrical circuit, the value of the current intensity, the applied voltage and the electrical resistance of the circuit.


Quantities and units

Ohm's law, therefore, relates three electrical quantities that are represented in the following table together with their three units.

Voltage or Voltage (V) Volt (V)
Current Intensity (I) Ampere (A)
Electrical Resistance (R) Ohm (Ω)
Voltage or Voltage:

It is the energy with which a battery drives electrons through the circuit. When the voltage is higher, the energy is greater and therefore the electrons circulate faster, increasing the electric current.

The tension or voltage is measured in Volts.

Electrical resistance:

It is the opposition that a component presents to the passage of electric current. The greater the resistance, the more it opposes the passage of electric current and therefore the less current will pass through the circuit.

Electrical resistance is measured in Ohms.


It is the number of electrons that circulate through a conductor every second. The more electrons flow per second, the more current will pass through the conductor.

Current intensity is measured in Amps.

Ohm's Law Formula

According to Ohm's law, the current intensity (I) flowing through an electrical resistance (R) is proportional to the voltage (V) applied to the resistor and inversely proportional to the value of the electrical resistance.

Ohm's law written in mathematical notation is as follows:

I = \cfrac{V}{R}

Solving the previous formula, the other two forms of Ohm's law are obtained.

V = I \cdot R

R = \cfrac{V}{I}

A mnemonic that can be used to remember Ohm's law is the following triangle with the three magnitudes:


Covering the magnitude that we want to find out, the corresponding formula appears. For example, if we want to know how much current is worth, we cover the letter I and the letter V can be seen above the letter R. This means that I = V / R.


Simple exercises to calculate circuits with Ohm's law.


Ohm's law exercises. PDF format

Ohm's law exercises. KiCad format


Multiple choice quizzes on Ohm's law: