Hello, my name's Dr.

George, and this lesson is called "An electric motor".

It's part of the unit Electromagnetism, and in this lesson you're going to make an electric motor.

The outcome for the lesson is: I can explain how connections in a motor enable its coil to be driven continually in one direction.

So you're going to learn why the coil of a motor keeps on going round and round.

Here are the keywords for the lesson, which I'm not going to explain now because I'll introduce them as we go along.

But this slide is here in case you want to come back any time and check these meanings.

There are two parts to the lesson: making an electric motor and the working of an electric motor.

Let's get started.

An essential part of an electric motor is a coil of wire, and we place that coil of wire in a magnetic field, and then the coil spins around when an electric current flows in it.

And it spins because a coil of wire with a current in it has a magnetic field around it, but we've placed it into another magnetic field, and the two magnetic fields interact with each other, and that causes forces to act on the coil.

So here's the coil.

It's wrapped around a block that's made of plastic or wood that's just convenient for holding the coil in shape and also enabling it to keep rotating.

This axle runs through the middle of the block, and the coil can spin around on this axle.

Then we have two electrical contacts.

That's to connect the coil to the power supply or battery.

And this yoke is a U-shaped piece of steel that's simply a convenient shape for holding the two magnets in place.

And these two magnets aren't bar magnets.

They're a type of magnet that have their north-seeking and south-seeking poles on the largest flat face.

And if we use magnets like this and position them the way we have here, north facing south, we get a uniform magnetic field between them.

That's a field in which the field lines all point in the same direction.

They're parallel and they're equally spaced.

Focusing in on the coil, it's made of insulated wire, wire that's coated with plastic or some other non-conducting material.

And the rod through the centre of the core is also insulated so that electric current can't take a shortcut between the contacts, because both of the contacts touch the rod.

So all of this is to make sure that the current is forced to go around and around the turns of the coil.

So here are the two contacts, the rod between them.

So we don't want current to flow directly from one contact to the other.

We want it to have to go around through the coil.

To hold the contacts in place up against the rod, we use tiny elastic bands.

And which parts of a motor coil, which of these parts are electrical insulators? Contact, rod, wire casing, wire core.

For these short questions, I'll wait five seconds, but if you need longer, just press pause, and press play when you have your answer ready.

The correct answer is the rod and the wire casing, the coating on the wire.

And when you make your own electric motor, which I'm going to ask you to do shortly, you'll start by setting up this.

You'll wrap your wire around this central part.

The ends of the wire need to be bare, and you'll hold them against the rod using two little elastic bands like this so that they're sitting on either side of the rod.

And now you need your coil to be able to spin.

So you'll take a long metal axle, that's just a thin metal rod, and you'll pass that through the rod that is attached to your coil, which is hollow, and that means your coil will be able to spin freely.

Then you have these two contacts.

They're just pieces of wire, and they go off to the battery or the power supply that you're using, and they're bare at the ends.

And as you can see, they're curved, they're curving outwards like this.

And you can curve them between a finger and thumb.

And these wire contacts make the electrical connection between the coil and the battery or power supply because you're going to want a current to flow in this coil.

We have the wires held against the base using these metal studs, so they're held securely in place and the way they're curved, they will make a good connection with the ends of the coil and they'll tend to spring back towards the coil all the time.

So now the coil can spin without any wires tangling.

And now a question: why are the contacts shaped into a curve and pressed against the coil rod and held in place by metal studs? Read each option carefully.

Press pause if you need longer than five seconds and press play when you're ready.

It's true that this gives us good electrical contacts between these pieces of wire and the ends of the coil.

It's also true that this enables the coil to spin without any wires getting tangled.

And it's also true that these contacts enable electricity to flow through the coil as it spins.

So in fact, they're all true.

Did you spot that? Now we have this U-shaped piece of iron.

It's actually called a yoke.

It can be iron or it can be steel, and it holds these two particular type of magnets.

You could call them motor magnets.

And these are magnets that have their poles on their large faces.

And what you'll need is the north-seeking pole of one to be facing the south-seeking pole of the other.

That gives you a uniform field, which is what we need.

If you have like poles facing each other, you'll have a field between them, but it won't be uniform, and your motor won't work.

So here's what that uniform magnetic field would look like when it's represented by field lines.

Evenly spaced field lines all pointing in the same direction.

So we fit the yoke over the base of the motor.

It'll be designed to fit nicely.

So that the magnets are in the correct position, they should be either side of the coil.

Now, which of these diagrams shows a uniform magnetic field between the two motor magnets? Press pause if you need more than five seconds.

The answer is C.

It's the only one where we have all the field lines with arrows in the same direction and they're evenly spaced.

Now I'd like you to go ahead and make an electric motor using a motor kit.

Connect your motor to a three-volt DC electrical supply, and you'll need to give it a push to start it spinning.

So press pause, and press play when you've done that.

I hope your motor is working nicely.

It can take a while to get it sorted out.

There's a little video here if you want to watch one in action.

And now for the second part of this lesson, the working of an electric motor.

So in the coil, current flows into the coil, around the coil, and out of the coil, as shown by these yellow arrows.

Now do you remember Fleming's left-hand rule? You can use it to predict the direction of the force on a wire that carries a current in a magnetic field.

And if we use it, we'll find that the right hand side of this coil experiences a downwards force, and the left hand side experiences an upward force.

If you'd like to check that for yourself, you'll need to remember that with Fleming's left-hand rule, you take your left hand and you have your first finger, second finger, and thumb all at right angles to each other.

And you point your first finger in the direction of the magnetic field that's following the arrows of the magnetic field lines, which will run from north-seeking to south-seeking.

And you point your second finger in the direction of the current.

So choose one side of the coil, point your second finger in the direction of the current.

To get both of those fingers pointing in the right way, you might have to bend your arm around in a bit of an awkward way, but it should be possible.

And then your thumb will be pointing in the direction of the force on the wire.

So if you'd like to check that, you can do that separately for each side of the coil.

Now together, these two forces are going to make the coil turn.

If you have equal and opposite forces acting on either side of an object, you will turn it.

It's a bit like how you turn a steering wheel.

And when the coil turns to become vertical, the electric contact is actually broken.

If you look at the picture here, the wire contacts are not touching the ends of the coil anymore.

That means there's no current in the coil, and that means there won't be any forces pushing it around.

That might seem like a disaster, but it's not because there'll be very little friction the way this motor is designed and so the coil will carry on turning.

Look at this picture.

When this coil is horizontal, the current flows away from you on the right hand side of the coil, and the coil is made to spin.

When the coil is next horizontal, the contact is made again.

The contacts touch the ends of the coil wire.

And again, the current flows away from you on the right hand side of the coil, and the coil gets pushed around.

So because of the way the motor is designed, the right hand side of the coil is always experiencing a current in the direction shown here.

So the coil is gonna get pushed in the same direction every time.

If you have the same current direction and the magnetic field is staying in the same direction, you're going to have the same force direction.

Now have a look carefully at these three diagrams. Which of these coils is being forced to spin? Press pause if you need more than five seconds.

At the position of the coil in A, the contacts are definitely touching the ends of the coil, and so there will be a current, and so the coil will experience forces that make it spin.

In B, it's not quite clear whether the contacts are touching the ends of the coil.

If they are, then there'll be a current and the coil will still experience forces.

If they're not touching, there won't be any forces.

And then C, it's very clear that the contacts are not touching the ends of the coil anymore, so there'll be no current in the coil and no force.

But remember, it will keep on going because it doesn't have much friction.

Now I'd like you to explain how a motor is forced to keep spinning in the same direction.

And to give this some structure, I'd like you to use these three diagrams. So for each diagram, describe what's happening.

And by doing that you're gonna tell the story of how a motor keeps spinning.

So take as long as you need to write down your answers, and press pause while you're doing that, and press play when you're ready.

Let's have a look at an example answer.

So in the first diagram, current flows around the coil, which is in a uniform magnetic field.

The coil is forced to spin clockwise.

In the second diagram, the contact is broken and no current flows around the coil, but the coil keeps turning because there is little friction.

And in the third diagram, the contact is remade and current flows around the coil in the same direction as before.

The coil is again forced to spin clockwise.

If you've got those points into your answers, well done.

And now we've reached the end of the lesson.

So I'll give you a summary.

An electric motor contains a coil of wire that spins round when an electric current flows through it, with connections that do not tangle.

It spins because it is in a uniform magnetic field.

Insulation around the wires makes sure the current flows around the coil.

Springy contacts make current flow through the coil when it is horizontal.

When it is horizontal, it is pushed around.

When it is vertical, contacts are broken.

They're made again when the coil is horizontal and is pushed round again in the same direction.

So well done for learning about a motor and for making one yourself.

I hope you enjoyed the lesson, and I hope to see you again in a future lesson.

Bye for now.