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:
Playstation
Cell Phones
Circuits
• Ohm’s Law is the basis for how all circuits
function.
• Examples of Circuits:
Playstation
Cell Phones
Computers
Circuits
• Ohm’s Law is the basis for how all circuits
function.
• Examples of Circuits:
Playstation
Cell Phones
Computers
Anything that gets
plugged into a wall
or a battery has a
circuit
Making sense of circuits
• The best way to imagine a circuit is to think of
traffic!
Electricity Terms
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Electrons
Current
Resistance
Voltage
Wires
If electricity is like
traffic, what would
the cars be??
Making sense of circuits
• Electricity comes from moving electrons.
• Cars are the electrons on the road.
-q
Electricity Terms
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•
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Electrons
Current
Resistance
Voltage
Wires
Cars drive on the
road. What
represents the road?
Making sense of circuits
• Wires are the roads that electrons travel
along.
Electricity Terms
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•
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Electrons
Current
Resistance
Voltage
Wires
The gas in a car is
the Potential Energy
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
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•
•
•
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Electrons
Current
Resistance
Voltage
Wires
The cars are all
driving at one speed
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
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•
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Electrons
Current
Resistance
Voltage
Wires
In traffic there’s
always construction
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
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•
•
•
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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)
10Ω + 10Ω + 10Ω = 30Ω
A
B
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?
Just 10Ω.
A
B
Traffic Report
• Some electrons will take Route A, and some
will take Route B.
A 30Ω
B 10Ω
Traffic Report
• To get our total resistance (the “Traffic
Report”), we will add them together like this:
1
1
1


Rtotal 30 10
A 30Ω
B 10Ω
Traffic Report
• To get our total resistance (the “Traffic
Report”), we will add them together like this:
1
1
1


Rtotal 30 10
1
 0.13
Rtotal
1  (0.13)( Rtotal )
7.5  Rtotal
Practice
• Find the total resistance for this circuit:
• Let each bulb have a resistance of 1Ω.
Practice
• Find the total resistance for this circuit:
1  1  1  1  4
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:
1
1
1


Rtotal
1 1
1
2
Rtotal
1
  Rtotal
2
A=1Ω
B=1Ω