# Ohms Law for Dummies

5,447

23

3

Hey! Dont be so hard on yourself!

You're not dumb! Electricity is an extremely difficult concept to understand, which is why today you're going to learn from me (A Dummy), how I learned the fundamentals of electricity. Ill cut out all the excess and leave you with just the simplified fundamentals.

Today Im going to cover just a brief intro to electricity, we'll cover

1. What is electricity?
2. Voltage Current Resistance and Power
3. The algebraic relationship to each other Ohms Law
4. And My favorite method of solving circuit problems!

Why should you listen to me? Ive been an Electrician for 6 years and I once sat in your very spot! I wanted to understand electricity, but people kept using big terms and foreign concepts that went right over my head! So today Im going to teach you what I wish someone taught me when I was just starting. The basics, but..basic-er

### Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

## Step 1: What Is Electricity?

Electricity is the movement of electrons. That's it. Simple enough right?

Without getting too deep, everything in the entire universe is made of atoms. At the core of the atom you have Protons and neutrons, and in a cloud around them are electrons!

Here's the thing. Electrons don't like each other. Electrons have a negative - charge, and when you put them together they tend to push each other away!

But, Electrons love Protons! Protons have a positive + charge, but cant move around as easily as electrons can. So if you put an electron and proton together, the electron will move towards the proton! Electricity!

Remember the old saying? Opposites attract?

So with that out of the way, now we can get to the building blocks of electricity (extremely simplified for our lesson)

1. Voltage: An imbalance of of charge between two points
2. Current: Amount of electrons flowing past a point
3. Resistance: Resistance to the flow of electrons
4. Power: Transfer of electric energy into another form

And how we measure them

1. Voltage: Measured in Volts (V)
2. Current: Measured in Amps (A)
3. Resistance: Measured in Ohms (Ω)
4. Power: Measured in Watts (W)

And their symbols

1. Voltage: Given the symbol (E or V) for Electromotive Force or Volts
2. Current: Given the symbol (I) for the Intensity of flow
3. Resistance: Given the symbol (R) for Resistance
4. Power: Given the symbol (P) for Power

Keep in mind this is just and intro and you can go much more in depth into your explanation and definition of these terms however, why not just keep it simple?

So how do they work together?

My favorite way to explain this is to imagine electricity as a tank of water going through a hose. The force pressing down on the water, or the pressure is Voltage. Because of this pressure, water is going to flow, the amount of flowing water is Amperage. But at one point in the hose, there is a kink! Less water can flow through here, causing Resistance. Now imagine you spray the water at a waterwheel, causing it to spin, Power!

Now that you know the terminology, we can get into the mathematical relationships

## Step 2: Ohms Law

Ohms law describes how Voltage, Current and Resistance relate algebraically, stating

Voltage (E) = Current (I) multiplied by Resistance (R)

E=IR

or you can rewrite it many ways

I=E/R R=E/I

So lets do an example, We have a circuit consisting of a 12v Battery and a resistor measuring 2 Ohms. If we plug this into our equation it should look like this: 12v=I(2Ω). Divide 12v/2Ω and I = 6. 6 Amps will flow!

Now lets try it again, This time you use the same 12v Battery, but this time you don't know the resistance! Using an ammeter, you measure a flow of 1 amp, how much is the resistance? Plug it into our equation: R=12v/1A and we get R=12Ω!

Last one, this time we plugged a circuit into a battery of unknown voltage (Never do this by the way) You know the Resistance is 6Ω and you measure the flow as 2 Amps. Plug it into our equation E=2a*6Ω and we get 12v! That's simple enough right?

Now here's a fun little trick Draw a circle and draw a line horizontally in the middle. Leave the top half alone and draw a line vertically in between the bottom half. You should have the worst looking peace sign you've ever drawn! However this is useful, trust me! On the top half put an E, on the bottom left quarter put an I, and the right quarter put an R. Now, depending on the value you need, place your thumb over the symbol and you will get your answer! For example you need voltage? Cover the E and you are left with I multiplied by R! You need Resistance? Cover the R and you are left with an E/I!

Pretty cool huh?

Now lets add power into the equation!

## Step 3: The Power Formula

The power formula is as simple as ohms law

Power(P) is equal to Current (I) multiplied by Voltage (E)

or P=IE, we can rewrite this just as we did with ohms law!

I=P/E and E=P/I

Lets do some example!

A circuit has a 12v battery and a current flow of 2 Amps. By plugging this into our power formula P=(2A)(12v) and we get 24 Watts! Wow! Most like the power is turning into heat from our circuit!

and another example is using that same 12v battery in a circuit, we use a wattmeter and measure 48 watts! How much current is flowing? Plugging what we know into our power formula, we get (48W)=I(12v), giving us 4 Amps of current!

and last but not least lets say in a circuit with unknown voltage, you measure 240 Watts and a current flow of 1 amp, whats the applied voltage? Plugging it in we get E= (240w)/(1A), giving us 240 Volts! Ouch!

Also its important to note that you can plug this into the circle we drew last time, just substitute E for P and R for E

But now lets get to my favorite method of ohms law!

## Step 4: PEIR

PEIR will solve all your problems! In my opinion its the best method however most people have never used PEIR

First write out PEIR vertically

P (Power)

E (Voltage)

I (Current)

R (Resistance)

And fill in the values you know, Lets say we have a 120v with a resistance of 60Ω, Plug it in!

P=?

E=120v

I=?

R= 60Ω

Now to go up with PEIR we multiply, and to go down, we divide. So lets start from resistance and go up. 60Ω multiplied by an unknown number will give us 120v. 120v=60Ω*I, therefore we get 2 Amps! So we plug that in!

P=?
E=120v

I= 2A

R= 60Ω

Now lets get Power! Remember going up means you multiply and going down means divide, so 120v multiplied by 2 Amps should give us our power, 240 Watts!

P=240W

E=120v

I= 2A

R= 60Ω

And thats it!

## Step 5: Next Lesson?

And thats how you can use Ohms Law to solve for problems!

That wasnt hard at all was it? You just took your first steps into the world of electricity! Congrats!

However, dont stop here! Theres so much more to learn, I recommend starting with instructable user RANDOFO's instructable on electronics

And maybe if I can find some more time Ill make another lesson for you!

Let me know if you would like another lesson! Up next Series Vs Parallel?

## Recommendations

• ### Large Motors Class

13,257 Enrolled

## 3 Discussions

Hil

This is very good, however i'm having trouble understanding step 4. What do you mean by 'going up you multiply and going down you divide'

Also, could you explain the formulas in the outer circle of your PEIR diagram.

Thanks Maurie