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These are some great vintage racecars.
We're here at the Georgia Racing Hall of Fame
in Dawsonville
to see how we harness electricity and magnetism
to get where want to go.
We're looking at generators and motors
in this segment of Physics in Motion.
You may not have known,
but generators and motors are not the same thing.
We're gonna use this vintage car
to help explain the difference.
Let's look under the hood.
We're first of all interested in the generator,
which is right here.
It takes mechanical energy from the engine
and turns it into electricity
to run the lights, and wipers,
and all the electrical systems in the car.
A motor works the opposite way.
It takes electrical energy
and turns it into mechanical energy.
So motors and generators are the reverse of each other.
We'll get into more detail on all this a little later.
But, first, let me explain the difference
between a motor and an engine
because many of us use those terms interchangeably.
Technically, an engine runs on fuel,
like gasoline.
Motors, on the other hand, use electromagnetic induction.
So if it needs chemical fuel,
it's an engine.
If it doesn't, and it runs on electricity,
it's a motor,
whether it's your electric toothbrush
or a Model S Tesla.
So, now, let's talk about how most cars,
electric cars excepted,
use generators and motors.
It might be a little different than you think.
Before about 1960,
most cars used generators
to drive the electrical system
and gas to run the engine.
Most modern cars use an alternator,
which is a slightly different kind of generator
for the electrical systems.
But motors and generators both use electromagnetic induction
in which voltage is induced by a changing magnetic field.
Okay. So you know that electricity can generate
a magnetic field and vice versa.
But what you may not know
is that this discovery hundreds of years ago
led to figuring out how to build a car,
and it starts with a man named Michael Faraday.
He's the guy who invented the generator,
which changed just about everything
having to do with machines and how they work.
Today he's considered one of the greatest scientists
who ever lived.
One of his many legacies is called Faraday's law.
It predicts how a magnetic field will interact
with an electric circuit
to produce an electromotive force,
or EMF.
This interaction results in the phenomenon
we call electromagnetic induction,
which creates a current in a circuit
when there is relative motion
between the wire and the magnetic field.
I'll show you in a simple demo.
When I put this magnet through this wire loop,
the changing magnetic field creates a current in the wire.
You can see it here on the voltmeter.
It induces a voltage,
and that difference in potential
causes current to flow.
You can also see how electric current induces magnetism
with this wire, nail, and battery.
Normally this nail is not a magnet.
But when it's wrapped in a coil of wire,
and I cause the current to flow
by attaching it to a six-volt battery,
it becomes a temporary magnet.
Now let's get into more of the guts of motors and generators.
We'll start with motors.
The most basic type of motor is a DC,
or direct current motor.
Direct current is electrical current that runs
in only one direction.
Current travels from a battery
and moves through wires called brushes
because in the old days, they actually were brushes.
Today, there are also brushless motors,
which use digital censors to perform the same task.
The brushes sit on a piece of metal
called a commutator.
The commutator is a split ring usually made of copper
that is connected to wire loops known as the armature.
The commutator armature assembly is known as the rotor,
which rotates at the center of the motor.
The brushes, or censors, are connected to the battery
and make contact with the commutator as it turns,
supplying it and the armature with current.
This assembly sits in a stationary magnetic field
that is created by the stator,
made of either a permanent magnet
or coil-wrapped metal plates that surround the rotor.
The field exerts a magnetic force on the wires,
which causes the rotor to turn.
When the rotor has made half a turn,
the current begins to flow in the opposite direction
because the commutator is now touching
the opposite side of the battery.
This electromechanical process by which
direct current is turned into alternating current
is known as commutation.
That reversal of current causes the magnetic force
acting on the rotor to reverse direction.
When it reverses, it makes the rotor spin.
That motion, that mechanical energy,
can turn a shaft, which is connected
to many things to make them run.
Your house probably has at least fifty motors in it,
running everything from power tools and fans
to household appliances and electric cars.
There's another type of motor,
an induction motor,
that runs directly off alternating current.
Compared to DC motors, induction motors are simpler
and have fewer parts,
no brushes, and no commutator,
which makes them more reliable and longer-lasting.
While induction motors run on alternating current,
DC motors run off direct current
and are used whenever the motor
is battery-operated.
This is the stator, which in this kind of motor
is made of laminated magnetic metal plates.
It doesn't move.
It's stationary just like in the DC motor.
Copper, or other metal, is wound through
to form a coil.
Sometimes we call them windings.
The more loops the windings have,
the greater the magnetic field is through them.
When you hook up the alternating currents to the stator
the changing nature of the current flow
creates a rotating magnetic field around it.
The stator doesn't move, just the field around it.
Like DC motors, induction motors have
a rotor at the center made of copper wires.
Remember, Faraday's law tells us that
the changing magnetic field created by the stator
induces voltage in the rotor.
And because of that induced voltage, the rotor,
located at the center of the motor,
becomes a current- carrying loop.
The changing magnetic field around the stator
exerts a magnetic force on the current-carrying rotor,
which causes it to rotate.
As the magnetic field moves around the rotor,
it exerts a force in just the right place
to cause the rotor to continue to rotate.
That's what causes the rotor to spin continually,
exerting a force on the wires at just the right time
to create optimal power.
We've seen that electricity and magnetism
are intrinsically related.
Alternating current flowing through the wire and the stator
creates a changing magnetic field.
And, conversely, current flows in the wires of the rotor
because of this magnetic field.
All motors function in much the same way
in that they all need changing magnetic fields
to create motion within the rotor.
The fundamental difference between induction and DC motors
is that the changing magnetic fields
in an induction motor
are caused by the alternating current
that is supplied to the stator.
In a DC motor, the changing magnetic field
is caused by commutation, which, as you recall,
is the mechanical transformation of the direct current
from the battery to alternating current
through the brushes and commutator bars
on the armature that make up the rotor.
Let's step back a second and think
how we could make this motor even more powerful.
Let's use the equation that allows us to find
the magnetic force exerted on a current-carrying wire,
where magnetic force equals
current times the length of the wire
times the magnetic field's strength.
We could make the magnetic field stronger,
or we could increase the length of the wire.
Or we could add more charge and increase current.
Of all these options, the easiest one
is to increase the length of the wire.
We do this by stacking loops of wire
on top of each other
in the coil that we've talked about.
Each loop contains moving charge
that experiences a magnetic force.
The more loops, the stronger the net force of the rotor,
and so the more powerful the motor.
Now that we've seen how motors work,
let's take a look at how generators work
opposite the way motors do.
They take mechanical energy
and turn it into electrical energy.
This is a generator.
It's found in classic cars built before 1964.
Just like certain types of motors,
it has a rotor made of an armature and a commutator
that are in contact with brushes
and an electromagnetic stator that surrounds the rotor.
The difference is the armature rotates
through mechanical action provided by the engine,
being linked to it through a pulley.
There's a residual magnetic field within the stator
that provides the initial push to start current
flowing through the armature as it rotates.
Some of the current produced by the moving armature
flows to the stator,
strengthening the magnetic field
and increasing output.
In this car, the excess current from the armature
is used to power things like headlights and turn signals,
as well as charge the car's battery.
There are many different kinds of generators,
but they all follow the same principle,
taking mechanical energy
and turning it into electrical energy.
So question, between motors and generators,
which one do you think supplies electricity
to your home?
That would be a generator.
So a power plant consists of an electrical generator.
Something has to spin the rotor within that generator.
It might be a waterwheel in a hydroelectric dam,
a large diesel engine, or a gas turbine.
But in most cases, the thing spinning the rotor
is a steam turbine.
The steam might be created by
burning coal, oil, or natural gas,
which heat the water to create the steam.
Or the steam may also come from the heat generated
by a nuclear reactor.
And the electricity that results is in the form
of an alternating current.
Alternating current, or AC,
is current that reverses direction
multiple times per second.
In the United States,
that happens 60 times per second,
or 60 hertz.
AC power uses high voltage
to move the electricity long distances.
During transport, the voltage is so high
that it's too dangerous to use
in residential or even commercial use.
A power plant creates electricity
that can be stepped-up
or increased to as much as 500,000 volts.
But by the time it gets to your house or business,
it's either 240 or 120 volts.
How do they do that?
Companies use transformers
to lower the voltage to a manageable level.
By the time it gets to you,
the voltage has been stepped-down
by transformers several times
so that you can safely run
all the electrical devices around you.
We've talked about the difference
between generators and motors,
how they mirror each other in some ways.
But both supply us with the energy we need
to power our world.
And we saw some really great cars while we were here.
That's it for this segment of Physics in Motion.
We'll see you guys next time.
(announcer) For more practice problems,
lab activities, and note-taking guides,
check out the Physics in Motion toolkit.