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?

“VRIIIIIIIIIIII!”

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.

Return from Ohms Law to Electronic Schematics

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Dipo says

Why didn’t you convert the 3mA to Ampere before evaluating in the second examlpe?

Dipo says

Kindly help remove my comments. Gosh! I suck at math.

admin says

I’m glad you figured it out =)

Oyvind

vamsi says

because if we covert 3mA to Amphere we have do a long process

jake says

Hey im new to the whole electronics thing was wondering if anyone could mentor me?

jake says

If so email me, jakeyboy1661@gmail.com

Abdul Latif says

Hi sir I like electronics kindly help me how to make a circuit on pcb is there any software for it?

Thanks.

admin says

Yes,

check out http://www.build-electronic-circuits.com/pcb-design/

Cheers!

Oyvind

SnowBerry says

Hi. I am not so new to electronics but I didn’t have enough recourses to play around with the various components. Keep being awesome and make more interesting articles about electronics:D

admin says

Thanks!

SnowBerry says

Hello Øyvind! I am new to all of these concepts and I really need some help. I have considered joining a robotics club. Please keep on making awesome article about electronics!:D

admin says

Join the robotics club! It sounds awesome =)

Oyvind

Seair says

Hi. Hoping you can help.

I’m using three(3) 1.5V bulbs(not leds) running off of one(1) 1.5V AAA battery.

When I start with a brand new battery, the bulbs are nice and bright. However, after about 2 minutes, I can notice the bulbs all starting to get dimmer. They’re just about completely out after 30 minutes.

Would using resistors keep the bulbs burning at a more equal brightness from start to ending of the battery?

I believe they are wired in parallel. Would it matter if in series or parallel?

Thanks,

Seair

Nick says

Stupid question, in the second example

we had a current, I, or .03 and a resistance of 600. Multiplied they give us 18. How do you know to make it 1.8 volts?

admin says

Hi Nick,

3 mA is 0.003 A (so you were lacking a zero 😉

Best,

Oyvind

Bunky says

Hi,

I am nerd in electronics, but I guess my maths is good.

If 1000mA = 1A

then 100mA = 0.1A

10mA = 0.01A

implicates

30mA = 0.03A

so howcome your statement, it is 30 mA is 0.003 A (so you were lacking a zero 😉

Am so confused…

admin says

@Bunky;

Oooops! Sorry, that was a mistake by me. I’ve edited my comment now.

3 mA is 0.003A.

30 mA = 0.03A

louis says

Great little website ….really happy i found it

Bunky says

V = RI where V = 1 volt, R = 1 Ohms, I = 1 Ampere

========================================

Given example, R = 600 Ohms, I = 3 mili Ampere

1000mA = 1A, then 3mA = 0.003A

On putting the values

V = 600 (R) x 0.003 (I)

V = 1.8

🙂

admin says

Exactly =)

ismaili seleman jafo says

its good and educated

vamsi says

because if we convert it it will be a long process

kiprono says

I am really new for electronics but i have a little ideas over this. my questions is under programming how can understand it? Am a first year pursuing computer science. my email is mitekenneth@gmail.com

regards

Kenneth

Chris says

Nice site.

In your example, 12v batt and 600ohm resister, you determine current is .02 (20ma)

What if batt was a 3.7v battery (with say 3000mah)

admin says

Hey,

The 3000mah just tells you how much energy your battery can store. It doesn’t affect this calculation. So just switch 12V with 3.7V:

3.7V / 600 ohm = 0.006A = 6mA

Best,

Oyvind