Circuits Series and Parallel. Ohm’s Law In a very isolated situation, we know that: V = IR But how...

Circuits

Series and Parallel

Ohm’s Law

• In a very isolated situation, we know that:V = IR

• But how does this apply to the real world?

Circuits

• Ohm’s Law is the basis for how all circuits function.

• Examples of Circuits:

Circuits

• Ohm’s Law is the basis for how all circuits function.

• Examples of Circuits:Playstation

Circuits

• Ohm’s Law is the basis for how all circuits function.

• Examples of Circuits:PlaystationCell Phones

Circuits

• Ohm’s Law is the basis for how all circuits function.

• Examples of Circuits:PlaystationCell PhonesComputers

Circuits

• Ohm’s Law is the basis for how all circuits function.

• Examples of Circuits:Playstation Anything that getsCell Phones plugged into a wallComputers or a battery has a

circuit

Making sense of circuits

• The best way to imagine a circuit is to think of traffic!

Electricity Terms

• Electrons• Current• Resistance If electricity is like• Voltage traffic, what would• Wires the cars be??

Making sense of circuits

• Electricity comes from moving electrons.• Cars are the electrons on the road.

-q

Electricity Terms

• Electrons• Current• Resistance Cars drive on the• Voltage road. What • Wires represents the

road?

Making sense of circuits

• Wires are the roads that electrons travel along.

Electricity Terms

• Electrons• Current• Resistance The gas in a car is• Voltage the Potential

Energy• Wires that makes it go.

Which is the gas?

Making Sense of Circuits

• Voltage is like how much gas you have. It determines how far you can go and how long your car can run.

V

Electricity Terms

• Electrons• Current• Resistance The cars are all• Voltage driving at one

speed• Wires or another.

What is speed representative of?

Making sense of circuits

• Current is the speed of the cars going down the road.

I

Electricity Terms

• Electrons• Current• Resistance In traffic there’s• Voltage always

construction• Wires that slows the cars

down.

Making sense of circuits

• Resistance is like roadwork on the road that slows traffic down. Remember: A resistor is anything that uses electricity.

R

Electricity Terms

• Electrons• Current• Resistance• Voltage• Wires

Making sense of circuits

• Imagine these two trips around the block:

Trip 1 Trip 2

Making sense of circuits

• Which trip will result in slower traffic speeds?

Trip 1 Trip 2

Making sense of circuits

• If these were circuits instead of a road map, it would look like this:

Trip 1 Trip 2

Making sense of circuits

• Everything that applies to the traffic applies to the circuit. Trip 1 is faster, so current is higher too.

Trip 1 Trip 2

Making sense of circuits

• Which trip has the most amount of slow downs?

Trip 1 Trip 2

Making sense of circuits

• Which circuit has the most amount of resistance?

Trip 1 Trip 2

Series Circuits

• These kinds of circuit are called Series Circuits.

Trip 1 Trip 2

Series Circuits• Series Circuits are like a one lane road. There’s

only one way to go, so you have to go that way. If you run into construction, TOO BAD!!

Making sense of circuits

• Now let’s look at a more complicated road trip:

Making sense of circuits

• Which path will more cars take, A or B? Why?

A B

Making sense of circuits

• Compare the current (car speed) and resistance (amount of construction) between A and B.

A B

Making sense of circuits

• And the circuit would look like this:

A B

Parallel Circuits

• These circuits are called Parallel Circuits. This is like a highway, where you can change lanes if one gets to slow.

Series vs. Parallel Circuits

• Let’s take a look at how different kinds of circuits will change things in the real world…

Traffic Report

• When we’re talking about traffic we want to know the overall delays, not what’s going on in each lane. (We don’t have all day!)

• We can describe a circuit by giving it’s overall resistance instead of listing each resistor as well…

Traffic Report

• If each construction zone takes 10 min to get through, what’s our total delay?

Traffic Report

• If each construction zone is a 10Ω light bulb, what is our overall resistance?

Traffic Report• For Series Circuits, you have to go through all the

delays, so we just add them up.

• Rtotal = 10Ω +10Ω +10Ω= 30Ω

Traffic Report• For Parallel Circuits, we have to handle things

a little differently because there’s more than one way to go. Consider this circuit:

A B

Traffic Report

• What is the total resistance if you take route A? (Each bulb is still 10Ω)

A B

Traffic Report

• What is the total resistance if you take route A? (Each bulb is still 10Ω)

A B10Ω + 10Ω + 10Ω = 30Ω

Traffic Report

• What is the total resistance if you take route B?

A B

Traffic Report

• What is the total resistance if you take route B?

A B Just 10Ω.

Traffic Report

• Some electrons will take Route A, and some will take Route B.

A B30Ω 10Ω

Traffic Report

• To get our total resistance (the “Traffic Report”), we will add them together like this:

A B30Ω 10Ω

10

1

30

11

totalR

Traffic Report

• To get our total resistance (the “Traffic Report”), we will add them together like this:

total

total

total

total

R

R

R

R

5.7

))(13.0(1

13.01

10

1

30

11

Practice

• Find the total resistance for this circuit:

• Let each bulb have a resistance of 1Ω.

Practice

• Find the total resistance for this circuit:

41111

Practice

• Find the total resistance for this circuit:

• Let each bulb have a resistance of 1Ω.

Practice

• Find the total resistance for this circuit:

A=1Ω B=1Ω

Practice

• Find the total resistance for this circuit:

A=1Ω B=1Ωtotal

total

total

R

R

R

2

1

21

1

1

1

11