Ohm’s law.

How to Use Ohms Law:


Ohms law was found by Georg Ohm and it goes a little something like this:

V = RI

V is voltage, R is resistance and I is current.

The law states that a voltage potential equals the current multiplied by the resistance.

It is used VERY often. It is THE formula in electronics.

You can switch it around and get R = V/I or I = V/R. As long as you have two of the variables, you can calculate the last.

How to remember Ohms law

A simple way of remembering things is to make a stupid association with it so that you remember it because it’s so stupid.

So to help you remember Ohm’s law let me introduce the VRIIIIIIII! rule. Pretend that your driving a your car really fast, then suddenly you hit the breaks really hard. What sound do you hear?


And this way you can remember V=RI 😉

A practical example

The best way to teach how to use it is by example.

Below is a very simple circuit with a battery and a  resistor. The battery is a 12 volt battery and the resistance of the resistor is 600 Ohm. How much current flows through the circuit?


To find the amount of current, we rearrange Mr. VRI and get I = V/R. Now we can calculate the current by using the voltage and the resistance.

I = 12 V/600 OhmI = 0.02 A = 20 mA (milli Ampere)

So the current in the circuit is 20 mA.

If you don’t like calculating things yourself, check out this calculator for Ohm’s law.

Another example

Let us try another example.

Below we have a circuit with a resistor and a battery again. But this time we don’t know the voltage of the battery. Instead we imagine that we have measured the current in the circuit and found it to be 3 mA (milli Ampere).


The resistance of the resistor is 600 Ohm. What is the voltage of the battery? By using our friend VRI we get

V = RI
V = 600 Ohm * 3 mA
V = 1.8 V

So the voltage of the battery must be 1.8 V.

Here is a image to well illustrate Ohm’s Law



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