Understanding Ohm's Law

A Graphic Example of Ohm's Law

So you are starting to learn about electricity. As a graphic example of ohms law we will use two bodies of water connected by a pipe.

How Ohm's Law Works - The Simple Explanation

We have been told and know that V=IR, but why does it work? This is a simple explanation of Ohm's law and why it works.

V=voltage

The easiest way to think of voltage is to call it potential. In fact, lots of people refer to voltage a potential. Voltage is the potential to do work. Imagine two bodies of water connected with a pipe. If one body of water is higher than the other then there is potential for water to flow from the high potential to the low potential.

I=current

Current is simply the transfer of something from one place to another. In the example with two bodies of water connected with a pipe, the current is the actual flow of water through the pipe between the two bodies of water.

R=resistance

Resistance is the, well, resistance. It is anything that opposes the flow of current. In the example of two bodies of water connected by a pipe, resistance is formed by the pipe. As the pipe gets wider, more current flows because the resistance gets lower. As the pipe gets narrower, less current flows because the resistance gets higher. If there were no pipe between the two bodies of water, then we woud say there is infinite resistance. No current would flow.

So now lets put it all together, and create ohm's law. Let's try to solve for I (current) based on what we know about voltage (potential) and resistance.

First we will start with voltage. If we think back to the example of two bodies of water connected with a pipe. If we move the higher body of water even higher, then we create more potential between the two bodies of water. If nothing about the pipe between them changes, then the water will flow faster. Therefore, if V goes up, I goes up.

Now we look at resistance. If we constrict the pipe by making it less wide then we get less water flow. We have increased the resistance of the pipe. Thus, if R goes up, I goes down.

Now we can put it all together:

I=V/R

This equation covers all of our requirements for the relationships between voltage, current, and resistance. If we rearrange the equation we get:

V=I*R

Let me know what you think or what helps you. 26 comments

mark cawley 8 years ago

as the pipe gets narrower the resistence gets higher so less water flows

Electrotechnik 7 years ago

Nice illustration. The best way to understand electricity is to compare it with a liquid.

jameel 7 years ago

its a best explanation

chris 7 years ago

As the pipe gets narrower the water would have to flow faster to maintain a constant mass flow rate

Kamal 7 years ago

Why V=IR is ohms law proof

PaulM 7 years ago

An excellent explanation - well done

Cory 7 years ago

To chris who said "As the pipe gets narrower the water would have to flow faster to maintain a constant mass flow rate" true, but to better explain this as the is a begginers tutorial you would have said if the pipe get smaller you would have to raise body of water "a" higher or body of water "b" lower or both to get the same mass flow rate as you would if the pipe was larger and bodies of water stayed the same.. otherwise new learners would be like "well how does it flow faster?" Tech terms would be "increasing current to compensate for the added resistence in order to maintain desired voltage"

Kelly 6 years ago

VERY useful explanation, it helped me a lot!

bob 6 years ago

very useful, thanks a lot! I had to explain Ohm's law to someone. Instead i just emailed them this link.

khalid khan 6 years ago

good but i can explain better than it.bye the way this was good explanation.

topdowgq 6 years ago

i need a lot of help with ohms law can someone help me

santosh 6 years ago

one of the best explanation I have read.

Mohit 6 years ago

An excellent explanation,it helped me a lot!

Rebecca 6 years ago

I have to do a presentation on this tomorrow and i need lot's of help this is quite a good explanation using the liquid it has made it very easy to understand thanks!

robert carter 6 years ago

i am a new student today we are in pararell & series circuits today . And i thought the basics was tough

JessicaPorter 5 years ago

cool, nice explainingg! =D you have been great help:P im doing a project which talks about Ohm's Law, i got a parnter named Drishti T. and shes good (NeRd)at this stuuf but we had the hardest time figuring out Ohm's Law..Thwanks Agaiin

swhat38 5 years ago

This was best explanation I ever came across, good job and thanks.

Mcdan Atuwo 5 years ago

I like this explanation it helps me a lot

jamie 5 years ago

I think you wanted to say in the paragraph about resistance that less water (current) would flow because the resistence is higher instead of "As the pipe gets narrower, less current flows because the resistance gets lower.

N. Grip. S 5 years ago

thanks a lot-- this helped me to finnish a school assignment, you explained it better and simpler than many other websites!! thanks again!

Confused :( 5 years ago

I don't get how this relates to electricity

ron 5 years ago

thanks for giving a wonderful basic concept of ohm's law

Sam 4 years ago

Thanks so much, that really helped with my science fair project!

jamez 4 years ago

dat wAz fantastic, i had few probs regarding ohms law but nOw em vEry much desperate to eXplain it to others bcz i le

arnt it quite well...............

Robort 4 years ago

Cut and paste error at:

As the pipe gets wider, more current flows because the resistance

gets lower. As the pipe gets narrower, less current flows because

the resistance gets lower.

... second (last) "gets lower" should be, "get higher".

Frank 3 years ago

That is great. only, I have a Question. The * between the i& the R? what does that mean?