Hello, my name's Dr.

George, and this lesson is called, "Applications of Electromagnets" and it's part of the topic electromagnetism.

The outcome for the lesson is I can describe how electromagnets are used in a range of practical applications.

Here are the keywords for the lesson.

I'm not going to read through all these definitions, because I'll introduce these words as we go along, but this slide is here in case you want to come back at any time and check the definitions.

I will start though by reminding you what an electromagnet is.

So it's a magnet that's made by having a coil of wire with a current in the coil and that has a magnetic field around it like a bar magnet, and if you put an iron core into the coil, you strengthen the magnetic field.

The lesson has three parts, moving metals, electric bell and simple electric motor, and every part is about a different application of electromagnets.

So let's start.

This photo shows a large and very strong electromagnet being used in a scrap yard to separate steel and iron from other materials.

And that's a useful thing to do, because about 40% of new steel that's made is made from recycled scrap steel and iron, and there's a lot of it because the bodies of cars are typically made of steel.

Steel is magnetic like iron, because steel is made mostly of iron.

It's an alloy, a mixture of iron with small amounts of other elements.

And the electromagnet can be switched on, brought over a pile of mixed metals and it will pick up only the steel and iron and then it can be swung to a different place and the electromagnet switched off so that it drops the pieces into another pile or onto a vehicle.

So you wouldn't want to use a permanent magnet here, because you could pick up the objects, but you wouldn't be able to drop them again.

An electromagnet is really convenient, because it's a temporary magnet.

It's not magnetic all the time, you can switch it on and off.

And this electromagnet can pick up a large number of pieces, large one, small ones, so you don't need people going around hand sorting these pieces of metal.

A magnet like this could be able to pick up a tonne of metal, that's 1000 kilogrammes, at the same time.

So which of the following items will not be picked up by an electromagnetic scrapyard crane? A steel pair of scissors, a car bonnet, an aluminium drinks can or an iron nail.

And with these short questions, I'll give you five seconds, but if you need longer, press pause and press play when you're ready.

And the correct answer is an aluminium drinks can.

It's the only one made of a non-magnetic material.

We have steel scissors, a car bonnet will be steel an iron nail, but aluminium is not magnetic.

Nickel and cobalt are the other two magnetic elements apart from iron and the electromagnet would pick up anything made of those, but you don't often get items made of those finding their way to a scrap yard.

Now for another application that uses movement of metal, but in a much smaller way.

In a block of flats, you may have an electric door lock on the main front door that you can open from each flat.

So if you want to let someone in, you just press a button instead of having to go downstairs and open it yourself.

And an electric door lock uses an electromagnet to pull back a bolt which unlocks the door.

So in this picture, we're seeing a cut through the door and the wall.

So the wall is the U shape of grey on the right, and inside the wall there's this bolt and electromagnet and right now the electromagnet is switched off and the bolt is sticking into the door.

The bolt has two springs attached to it that pull it over to the left.

And while the bolt's in the door, the door won't open.

It can't move either way.

But if we switch the electromagnet on, which we can do by pressing the switch in our flat when we want to open the front door, the electromagnet switches on and it attracts the bolt, which is made of soft iron.

And so it pulls the bolt to the right, pulls it out of the door and now it's possible to open the door.

There will always be a backup way of opening the door, so it will be possible to use some internal handle on the inside or a key to open it as well.

So now the bolt is pulled back, the door can swing open, and when the current's switched off, the springs pull the bolt back to the left and the door is locked again.

Now look at the position of the bolt in this diagram.

What will happen if the power supply to the electromagnetic door lock is cut off? Will the bolt stay still? Will the door be locked? Will the door be free to open? Press pause if you need longer than five seconds.

The correct answer is the door will be locked.

If the power supply is cut off, the electromagnet will switch off, it will stop attracting the bolt, which will be pulled to the left by the springs and that will lock the door.

So now a written task for you to use what you've learned about electromagnetic door locks.

Describe how an electromagnetic door lock can be used to open the front door of your block of flats to let your friends in without you having to go downstairs.

And then how would your friends be able to get in during a power cut? Take as long as you need.

Press pause and then press play when you're ready and I'll show you example answers.

So for the first question, how you would use the electromagnetic door lock to let your friends in while you're upstairs.

I would press a switch in my flat connected to the electromagnet in the door lock.

This would magnetise the electromagnet and it would attract the iron bolt, moving it to the right, unlocking the door so it can be pushed open.

When I stop pressing the switch, the electromagnet is demagnetized and the springs pull it back to the left to lock the door after my friend.

Now, you didn't have to write it in exactly the same way as this, but did you make the key points about magnetising the electromagnet, switching it on and it pulling the bolt to be able to open the door and then the electromagnet stopping being magnetic when you let go of the switch? Well done if you did.

And question two, how would your friend get in during a power cut? Well, you'd have to go down to the door and let them in.

There would probably be a handle on the inside that you could just turn or they could use a key if they had one.

Now let's look at another application of electromagnets, an electric bell.

This diagram may look complicated, but I'm going to explain what each part is and how it works.

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

So we have a switch and if we close the switch, we complete the circuit and current flows in the coil of the electromagnet.

Here's the electromagnet.

It's got an iron core and a coil of course.

Here's a contact point.

It may look a little complicated, but it's really just two metal parts and when they're touching, that completes the circuit.

The armature and a spring that's gonna pull the clapper down at the right time.

There's the clapper, the part that hits the bell, and there's the bell itself.

Let's look at how this bell works.

First, we have to press the switch and that completes the circuit so the electromagnet becomes magnetised.

Then it attracts the armature, which is made of a magnetic material and the armature bends upwards and that pulls the clapper upwards and the clapper hits the bell.

But then here's the clever part.

The contact there is now broken and so we don't have a complete circuit anymore, current stops flowing and the electromagnet switches off.

So it's no longer attracting the armature and the armature has a spring attached to it that pulls it back down.

But that completes the circuit again.

And we'll see what happens next in a minute.

But first a question.

What could the armature be made of? Copper, a magnet, soft iron or steel? Pause if you need longer than five seconds.

It could be made of soft iron.

Remember, soft here doesn't mean squishy.

It means a type of magnetic material that's easily magnetised and demagnetized.

So when the electromagnet switches off, the soft iron doesn't remain magnetised and so it's no longer attracted to the iron core of the electromagnet.

If you use steel, there is a risk that after the electromagnet switches off, the steel remains a little bit magnetised and would be attracted towards the iron core of the electromagnet and if the spring isn't strong enough, it might not be able to pull the steel away.

Of course, you wouldn't want to use a magnet and you wouldn't use copper, because copper's not a magnetic material, so it would never be attracted by the electromagnet.

Now let's have a look at what happens after the bell has rung once.

Actually, if you keep the switch pressed, the bell keeps ringing over and over again.

Here's what happens.

So we've seen how the bell rings once and then that breaks the circuit and the armature is pulled downwards, which completes the circuit again.

So now the electromagnet switches on and it attracts the armature back upwards, but that breaks the circuit so the electromagnet switches off and the armature springs back down, and this keeps on happening.

It doesn't stop until the switch is released.

So the bell rings over and over again and actually, it happens many times per second.

So it sounds almost like a continuous buzzing.

Now look at the diagram here.

What will happen if the contact point is closed and the switch is on? Press pause if you need longer than five seconds to think.

The correct answer is that the armature is attracted to the core, because we have a complete circuit and the electromagnet is switched on, so it attracts the armature.

A isn't right, a current never flows through the armature.

It's not part of the circuit.

So now can you complete the missing parts of this explanation to explain how an electric bell works? So parts of the explanation are here.

It begins with the spring has pulled the clapper down, but other parts are missing.

And you may need to say more than one thing in each of these boxes.

You can see that each of them is worth three marks.

So pause for as long as you need.

Press play when you're ready and I'll show you the answers.

Here are the answers.

So the spring has pulled the clapper down, that makes the circuit complete, the coil of wire becomes magnetised.

The electromagnet pulls the armature up.

You don't have to have said those exact phrases, but you do need to have made those points that those are the three key things that happen.

The clapper then hits the bell and then the circuit is broken.

The coil of wire loses its magnetism.

The spring pulls the clapper down, and that's a sensible order to write these things, because the circuit breaks and because of that, the coil or the electromagnet loses its magnetism and because of that, the spring can then pull the clapper down.

And finally, the clapper moves away from the bell.

So have a look and see how many marks you think you've got and well done if you've got most of those.

And now the last part of the lesson, a simple electric motor, and there's something for you to make here.

Many household appliances contain motors and a motor has some electromagnets that spin round because they are pushed by other electromagnets or by permanent magnets.

Their fields are interacting to make movement happen.

And you can find electric motors in an electric screwdriver, because part of that rotates when it's running, a vacuum cleaner, a washing machine and many other devices.

See how many you can think of.

Anything that you plug in or that you put a battery into and that moves or some part of it moves, is probably using an electric motor.

And you're going to make your own simple motor.

So I'll run through the instructions here and then I'll ask you to make the motor and you can come back and watch the instructions again if you need to.

First, here's what you need.

You need an AA battery, two identical safety pins, some small pieces of electrical tape which you'll stick to the pins like this, small piece of sandpaper, some insulate wire that you'll make into a coil and a small magnet, a type of magnet called a neodymium magnet, which is very strong for its size.

And first of all, you take your wire and wind it around a pen.

That gives you the right sort of diameter for your coil.

Make at least five turns but not too many more, because the coil won't spin very well if it's too bulky, too heavy.

Then loop the ends around the coil to hold the turns together.

You want quite a flat coil.

And now you're going to use sandpaper to remove the insulation from one end of the wire.

Remove it from about one and a half to two centimetres of the end of the wire.

And then on the other end, you're going to do something a bit strange.

You're going to hold the coil vertically like this, resting on the table and have the end of it resting on a block of wood and then stand off the insulation, but only from the top.

Again, about one and a half to two centimetres along, but only from the top of the wire, not the bottom.

And doing this is going to allow current to flow when it's needed, but not when it's not, and that's gonna help the coil to spin.

So now your wire coil should be like this.

You've got one end of the wire which is completely bare and the other end which is half bare.

And this coil is going to rest on two electrical contacts.

It's going to be resting on metal.

Like this, so those two little circles represent pieces of metal that the coil will be resting on.

And when the coil is this way up, can you see that no current will flow, because on the left side of the coil, we've got the insulate side touching the contact? But half a turn later, we have metal touching metal on both sides.

And I'm not going to go into detail about why we need this, but it is important that current flows half the time and not the other half of the time.

And that's going to make our coil want to keep spinning in the same direction.

Why are the ends of the coil sanded like this? Pause if you need more than five seconds.

The answer is to allow current to flow at the right times as it spins.

So next, you're going to tape a safety pin to each end of the battery, the way up that's shown here.

And safety pins are just a really convenient way to give us something to rest the coil on that are made of metal so that we get a complete circuit.

You're gonna thread the coil through the safety pins like this.

And we now have a complete circuit, this small circuit that includes the battery, the safety pins and the coil itself or at least when the coil is turned around the right way, we will get a complete circuit.

Check that the coil balances nicely in the pins, so just try flicking it and see if it spins freely.

If it wobbles a lot or if it stops quickly, you might want to adjust the wire slightly so that it spins better.

Now place the magnet below the coil on the battery and it will stick to the battery casing which is made of magnetic material.

And now you're ready to watch your motor run.

This is really impressive.

We just have these few simple items that we've put together, doesn't take long, and we actually have a working motor.

So you get the spinning started, but then it just carries on by itself.

And the energy for this motion is coming from the battery.

The reason the coil spins, is because the magnetic field of the permanent magnet interacts with the magnetic field around the coil.

And this is set up so that the wire isn't permanently attached to the safety pins, so that the coil can spin freely without the wire twisting and tangling as the coil spins.

So it can just keep on spinning without ever getting tangled.

In electric motors that you find in appliances, there are often sets of electromagnetic coils rather than just one and sets of permanent magnets, and these interact to make the motor spin.

And with clever designs, you can get a very powerful motor that can do hard work, it can exert large forces.

So here is the insides of an electric drill.

It's been taken apart, and on the left, we can see the electromagnet coils wound around a soft iron core and on the right we also have electromagnet coils.

So we used for our simple motor, a coil that was an electromagnet and the permanent magnet.

This drill is using two sets of electromagnets instead.

Now I'd like you to read these four statements and decide which statement is correct.

So press pause to give yourself enough time to read and press play when you're ready.

Do you have your answer ready? The correct statement is that all electrical motors have an electromagnet and either a permanent magnet or another electromagnet, or it could have sets of these, but motors have to have at least one coil, one electromagnet and then the other magnet is either permanent or an electromagnet.

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

Here's the list again of what you need and feel free to go back and watch the instructions again if you need to.

So press pause while you do that and press play when you're ready.

I hope your motor worked and I hope you enjoyed making it.

So it should be able to do this.

And now we're at the end of the lesson.

So I'll give you 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 fields of magnets to cause a force which makes the motors spin.

So I hope you've enjoyed the lesson.

I hope you'll look around you now to see if you can find any applications of electromagnets in your everyday life, and I hope to see you again in a future lesson, so bye for now.