Hello, my name's Dr.

George and I'm here to help you with this lesson called Using Electromagnets.

It's part of the unit Magnets and Electromagnets.

Here's the outcome for the lesson.

I can describe how electromagnets are used in cranes, locks, bells, and motors.

Here are the key words for this lesson.

I'm not going to go through them all now because I'll introduce them as we go along, but I will remind you what an electromagnet is.

So it's a magnet that's made by taking a coil of wire, wrapping it around an iron core, that's just an iron rod, and then putting a current through the wire.

If you do that, your core wrapped around the rod will behave like a magnet, in fact, like a bar magnet.

And when you switch off the current, it will stop behaving like a magnet, so that's an electromagnet.

There are three parts to the lesson called Moving Metals, Electric Bell and Electric Motor.

Let's get started.

Here's a photo of a scrapyard crane, or the end of a scrapyard crane, that is using an electromagnet to pick up pieces of iron, and it won't pick up non-magnetic materials such as copper or aluminium, so it picks up iron because iron is a magnetic material.

It's attracted to magnets, all magnets, including electromagnets.

And the iron can be conveniently dropped wherever you want to put it by swinging the crane around and then switching off current to the electromagnet, and then it will stop being magnetic and the iron will just fall off wherever you wanted to put it.

So an electromagnet is not a permanent magnet, it's not a magnet all the time.

It's only a magnet when the current is flowing in its coil, so we say it's a temporary magnet.

And it's very convenient because you can pick up a large number of pieces all at the same time, large and small.

You don't have to go around individually picking up all of these pieces.

And now I have a question for you.

Which of the following items will not be picked up by an electromagnetic scrapyard crane? A steel pair of scissors, a nickel coin, an aluminium drinks can, an iron nail.

You don't need special knowledge about scrapyard cranes for this, you just need to use knowledge about electromagnets.

I'll wait five seconds, but if you need longer, press pause, and press play when you're ready.

The correct answer is an aluminium drinks can.

What matters here is what each of these objects is made of.

Aluminium is a non-magnetic material.

It's just not attracted to magnets, but steel, nickel and iron are all magnetic materials, so they'll be attracted to the electromagnet.

Now for another use of an electromagnet that involves moving something, but this is much smaller.

What you're seeing here is a door and the wall next to it.

It's a strange view.

We're sort of looking from above with a cut through so we can see inside the wall.

So the wall's on the right, that sort of grey u-shape, and we can see inside the wall we have some objects.

And the door is on the left and there's a bolt into the door and it would stop the door from being able to open.

There's also an electromagnet on the right, an iron core with a coil of wire around it, but it's switched off right now.

And the reason why the bolt is staying in the door holding it closed is because of these springs.

So it's got these quite stiff springs and they're pulling the bolt towards the left and making it stay in the door, so the door is locked.

We can't move it either way.

But now if we switch on the electromagnet, it attracts the bolt, which is made of iron, and it pulls back the bolt towards the right.

And this is all designed so that the electromagnet is strong enough that it can pull the bolt to the right, even though the springs are trying to pull the bolt to the left.

And now the door is free to move.

We can open the door, it's unlocked.

And when we switch off the current, the electromagnet stops being magnetic, it doesn't attract the bolt anymore, and the bolt goes back towards the left.

The springs pull it back towards the left and the door is locked.

So instead of being operated by a key that you turn in a lock, this door lock could be operated by a switch, perhaps even by a remote control.

Now here's a question for you.

What will happen to the bolt in this picture if the power supplied to the electromagnetic door lock is now cut off? Will the bolt stay still, move left, or move right? Pause the video if you need longer than five seconds to think.

And the answer is that the bolt will move left.

The springs are trying to pull the bolt left and when the electromagnet switches off, there'll be nothing to hold the bolt towards the right anymore.

The bolt will spring back to the left.

Well done if you got that.

And now I'd like you to try putting the following statements into the correct order so that they describe how an electromagnetic door lock works.

So take as long as you need to do that, press pause, and then press play when you're ready.

And here's the correct order that tells the story of what happens.

A switch is pressed to allow current to flow in the electromagnet coil.

The electromagnet is magnetised and attracts the iron bolt.

The iron bolt moves to the right and unlocks the door.

When the switch is released, the electromagnet is demagnetized.

That means it stops being a magnet.

The bolt is no longer attracted and the springs pull it back into the locked position.

Well done if you got that right.

And if you didn't, you might like to take another look and see that it makes sense.

Now let's look at another use of electromagnets, the electric bell.

So an electric bell uses an electromagnet to make a clapper hit a bell.

Here are some of the parts.

We have a switch, and while that's pressed, current flows in the coil.

We have the electromagnet made of an iron rod and a coil wrapped around it.

Here's a contact point that completes the circuit.

It might look a little complicated, that part of the diagram, but these things are just pieces of metal, and when they're all touching, we have a complete circuit.

A soft iron armature.

You might not know the word armature.

This is a piece of iron that can easily bend.

Its springy and it's able to spring up and down.

And we have a spring that pulls the clapper down.

Here's the clapper and here's the bell.

So, let's check you were listening.

What is the name of the part that hits the bell to make it ring? Was it the coil, the armature, the clapper, or the core? Press pause if you need more than five seconds.

The correct answer is the clapper.

That's the part that hits the bell.

Now let's have a look at how this thing works.

First, somebody needs to press the switch down, and that makes a complete circuit with the green wire, including the coil, and also there's parts down at the bottom.

That makes one complete loop.

So there's now a current in the coil and the electromagnet becomes magnetised, starts behaving like a magnet.

And the soft iron armature, which is springy, it's bendy, is attracted to the electromagnet because iron is a magnetic material and it bends upwards and that pulls up the clapper, which hits the bell.

But then, here's the clever part.

The armature moving up actually breaks the circuit.

That little contact down at the bottom is no longer closed.

We don't have a complete loop anymore so the current stops flowing, so that means the electromagnet is no longer magnetised.

It no longer attracts the armature which comes back down.

And remember, there's that little spring attached to the armature.

That helps to pull it back down when the electromagnet lets go of it.

But, now when the armature comes back down, it completes the circuit again.

And so that switch is on the electromagnet, which pulls the armature back up, which dings the bell again, but that breaks the circuit, which turns off the electromagnet, the armature comes back down and this just keeps happening.

As long as the switch is pressed, this is going to go ding, ding, ding, ding, ding.

It's going to keep on ringing.

Now take a look at the diagram of the bell on the right, and I want to know what is going to happen if the contact point is now opened.

Will current stop flowing in the coil? Will the coil become magnetised? Will the armature be attracted to the core? If you need longer than five seconds, pause the video, press play when you're ready.

And the correct answer, if the contact point opens, that's going to make a gap in the circuit so current will stop flowing.

There'll be no more current in the coil.

Now I'd like you to try to tell the story of how this electric bell works, and in each of these rows, you need to pick a statement, and if you pick the right ones, then you'll be describing how the bell rings.

Three of the rows only have one statement in them, so there's nothing for you to choose, but in the other rows, there are two or three statements for you to choose from.

So pause the video for as long as you need and press play when you're ready and I'll show you the answers.

So the correct answers are the spring has pulled the clapper down, the circuit is complete.

The coil and the iron rod become magnetised.

The electromagnet pulls the armature up, the clapper hits the bell, the circuit is broken, so the coil and the iron rod lose their magnetism.

The spring pulls the clapper down and the clapper moves away from the bell.

Well done if you picked out those statements.

And if you didn't, or if you're just not quite sure, you could go back and watch again the part of the video where I explained the bell.

By the way, you may have noticed that the armature is made of soft iron and so is the core of the electromagnet.

Soft here doesn't mean squishy.

It means a material that easily becomes demagnetized when a magnet stops attracting it.

So we use soft iron for these parts so that when the electromagnet switches off, they stop attracting each other.

We wouldn't want them to continue to be magnetised and attract each other the whole time.

Let's move on to the last part of this lesson and there's something here for you to make.

Another device that uses electromagnets is an electric motor and these are found in many different devices.

Anything that you plug in, and that then does some movement, or anything that you put a battery in and does movement nearly always is using an electric motor, and these use the magnetic field around coils of wire and around magnets to make the movement happen.

So examples, an electric screwdriver, a vacuum cleaner, washing machine, also an electric fan, an electric toothbrush, and your phone when it buzzes.

These are all using motors.

Now I'm going to show you how to make your own motor.

So I'll run through the instructions now and then later I'll ask you to do this and you can come back if you need to and watch the instructions again.

So what you'll need is a AAA battery, two safety pins, the same size, and two pieces of electrical tape.

That's just a kind of sticky tape.

A piece of sandpaper, piece of insulate wire, which you're going to make into a coil, and a small neodymium magnet.

It's a particular type of magnet that's very strong for its size.

It's got north and south poles on its flat faces.

First you need to make a coil that's going to be your electromagnet, so wind the wire around a pen.

That gives you the right sort of diameter for this coil, and wind it at least five times to make five turns.

Don't do too many more than that because if the coil is too thick and heavy, this won't work as well.

So loop the ends around the coil to hold the turns together so the coil doesn't spring open.

We want it to be quite a flat coil.

And then you're going to use the sandpaper to remove the insulation from a couple of centimetres of one end of the wire.

Your insulation might be plastic, as here, or it might be a sort of transparent coating, but either way, you need to sand that off from the end a couple of centimetres.

On the other end, we need to be quite careful.

We do something a bit unusual here.

We're going to sand off the insulation, but only from half of the end.

So what you do is hold the coil vertically on the table, as shown here, and rest the end on a block, a wooden block, and then carefully sand off the insulation just from the top, so a couple of centimetres of the end, but just the top of it, not the underneath.

So when you've done that, it should look something like this.

One end is half bare, the wire is half showing, and on the other end it's fully bare.

Now I didn't say why, but can you think why I've asked you to sand the ends of the coil? Is it to make it lighter, to reduce friction, or to allow current to flow? If you need more than five seconds, press pause.

And the correct answer is to allow current to flow.

We've said this coil is going to act as an electromagnet, so we need a current to flow through it so we need to be able to make contact with the metal underneath the insulation.

Now next steps, you're going to tape a safety pin to each end of the battery like this, and then thread the coil through the safety pins.

So the reason for using safety pins is it's just a really convenient way to get a couple of loops at the end that you can thread the coil through, and they're made of metal so we have a tiny and full complete circuit here.

We have the battery, the metal safety pins, and the wire of the coil.

Check that the coil is well balanced in the pins so give it a flick with your finger and check that it spins easily.

If it wobbles around a lot or stops very quickly, then try to adjust it so that it spins better.

Just bend the wire a bit.

Now place the magnet underneath the coil onto the battery and it will stick to the battery casing because the battery casing is made of a magnetic material.

And nudge the coil to start it spinning and what you should see is it just keeps going.

I love it when that works.

It's such an amazing little thing.

It's just made of these very simple parts, but it's a real electric motor and it's getting its energy for the spinning from the battery.

And the reason the coil spins, I'm not going to go into detail about this, but just to say it's to do with the magnetic fields.

We have the magnetic field around the permanent magnet, the neodymium magnet, and we have a magnetic field around the coil 'cause the current flowing, and those two fields interact in a way that make the coil want to spin.

And the bare wire at the end is able to rub against the safety pin so we get a good electrical connection.

We have metal against metal.

But because the coil's not actually attached to the safety pin, it's just resting there, it doesn't get twisted.

There's nothing tangling as the coil spins so it can just go on and on spinning freely.

Now, many electric motors have not just one coil like yours, but many have a set of coils, and not just one magnet like yours, permanent magnet, but a set of them, but these interact to make the motor spin in the same kind of way as yours does.

Here we can see the inside of an electric drill.

And actually this one has, instead of permanent magnets and electromagnets, it has two sets of electromagnets and they interact to cause spinning.

Now, which of the following statements about electric motors is correct? All electric motors have a permanent magnet and an electromagnet.

All electric motors have two permanent magnets.

All electrical motors have two electromagnets.

Or all electrical motors have an electromagnet and either a permanent magnet or another electromagnet.

One of these statements is right.

If you need more than five seconds to think, press pause and press play when you're ready.

And the correct answer is D.

All electrical motors have an electromagnet, a coil, or at least one, and either a permanent magnet or another electromagnet.

So you need two magnets to interact, but you need one of them at least to be an electromagnet.

The other one could be a permanent or an electromagnet.

So now I'd like you to go ahead and build your motor.

Here's a list again of what you need.

And here it is again in action.

Give it a flick to get it started and off it goes.

So I hope your motor worked out well.

I hope you enjoyed making it.

And now we're at the end of the lesson, so here's a summary.

Electromagnets can be used to pick up and sort metals that are magnetic.

They can be used to move pieces of iron, such as door bolts, and are used in door locks.

An electric bell contains an electromagnet that pulls a clapper to hit the bell.

It automatically resets itself so the bell will keep on ringing if a switch is pressed.

Electric motors use the field of magnets to cause a force which makes the motor spin.

Well done for working through this lesson.

I hope you enjoyed making a motor and I hope to see you again in a future lesson.