Ohm’s law is the most fundamental law in all of electronics. It explains the linear relation between current, voltage and resistance in a circuit. These basic building blocks make your circuit do interesting work.
Georg Simon Ohm (1789 – 1854) was a German physicist, mathematician, and teacher. He found that there is a direct relation between a voltage applied across a conductor, the resistance, and electric current. This important relationship is what we know today as Ohm’s law.
Combining the elements of voltage, current, and resistance, Ohm came up with the following formula:
- V = voltage in Volts
- I = current in amps (Amperes)
- R = resistance in Ohms
Ohm defines the unit of resistance of 1 Ohm as the resistance between two points in a conductor where the application of 1 Volt will drive 1 Ampere of current. So voltage is the force that makes electrons flow (electrical current). But how much electrons can flow is dependent on the resistance between two points.
The more resistance, the less current, given the same voltage. Let’s take a look at an example.
Ohm’s law example
In the circuit below we have a 12 Volt DC power supply and a resistor. We don’t know the value of the resistor. What we do know is the current draw, which is 5.455 mA.
So now we can apply Ohm’s law to find the value of the resistor.
It seems like there’s a 2.2 kOhm resistor in our circuit.