Hello, my name's Dr.

George, and this lesson is called electromagnets, and it's part of the unit, magnets and electromagnets.

You might not know what an electromagnet is yet, but I'm going to show you, and then you'll make one and experiment with it.

Here's the outcome for this lesson.

I can describe how to make a magnet using an electric current, and you'll be able to describe it by the end because you will have done it.

Here are the keywords for this lesson.

I'm not going to go through them now because I'll introduce them as we go along, but if you need to check the meanings anytime, you can come back to this slide.

The lesson has two parts, an electromagnet and more turns on an electromagnet.

So let's start.

You might have realised that electromagnet sounds a bit like electric magnet, and an electromagnet has something to do with electricity.

But I'd like to remind you that the needle of a compass, which is a little moving magnet, is not affected by electrostatically charged objects.

What do I mean by that? I just mean objects that are positively or negatively charged.

Let me just show you again.

Here's a little plotting compass pointing north, and then we put a couple of positively charged objects next to it, and it's not affected.

It doesn't move.

That's because magnetic and electrostatic forces are different types of force.

But if we have flowing charge that's a current, and we see something different, is a compass underneath a wire.

And normally, the compass needle points to the earth's North Pole.

But every time a current switches on in this wire, it deflects the little magnet of the compass needle.

It moves it, so it points in a different direction.

So a current does affect a compass.

Here's a question.

Which of the following would not cause a compass needle to deflect? An iron nail, another magnet, earth magnetic field, or a positively charged balloon? I'll wait for five seconds, but if you need longer, press pause and press play when you're ready.

And the correct answer is a positively charged balloon.

The compass needle is a magnet, so it's affected by other magnets, which includes the earth, which is magnetic.

It's also affected by an iron nail because the magnet of the compass needle attracts the nail and the nail attracts the magnet back.

Now the reason why an electric current affects a compass is because electric current causes a magnetic field around the wire that's carrying the current.

And we know that we can represent that field like this.

So what we have here is lined magnetic field lines showing the shape of the field, and the arrows on the lines show the way a compass needle would point if we put it in that position.

If we switch off the current, if there's no current flowing, there's no magnetic field around the wire.

And if you have several wires all carrying current, you'll get a stronger magnetic field that's represented here by the field lines being closer together.

And you've probably experimented with making circuits with currents in the wires, but you probably didn't notice that there was a magnetic field around the wires.

You didn't see, for example, objects made of iron flying over and sticking to the wires.

And that's because it's not a very strong magnetic field that you get around the wires.

But we can increase the strength of the magnetic field around the wire by coiling it up, as shown on the left here.

And by making many turns of the wire all next to each other, we get a similar effect to what we saw on the previous slide of putting current carrying wires next to each other.

We strengthen the magnetic field.

And we can show that magnetic field by exploring it with a plotting compass.

Here's a simulation showing a coil attached to a battery.

There's a current in the coil.

And as we move the little compass around, it points in different directions, showing us what this invisible magnetic field is actually like.

And it turns out that the magnetic field around a coil of wire that's carrying a current is the same shape as the magnetic field around a bar magnet.

So these red lines here show the shape of a magnetic field.

And if you've ever investigated the magnetic field around a bar magnet, you will have seen, this is very much the same shape.

Now a true-false question.

The field from a current carrying coil is different to that from a bar magnet, true or false? And when you've decided, choose a reason that justifies your answer from the two given here.

Pause the video if you need longer than five seconds and press play when you're ready.

And the correct answer is false.

The fields are not different for a current carrying coil and a bar magnet.

They're the same shape and field.

And how would we know that? Because a plotting compass behaves the same around either a coil or a bar magnet.

As we move it around, we see the ways that it points are the same for both.

So we know we can coil up a wire and get a stronger magnetic field around it, but we can make the field even stronger by putting an iron core inside the coil.

And it's just a simple piece of iron in a rod shape.

But when you put one of these inside a coil wire carrying a current, we call it an iron core.

Core just means the centre of something, like an apple core at the centre of an apple.

So we can make an electromagnet like this.

We wind wire around an iron core, and each time we wind it around once, we can call that a turn.

So we can count the number of turns we have by how many times we wind the wire around the core.

So very simple equipment, you just need an iron rod, some insulated wire that's wire-coated in plastic, and some sort of power supply so that you get a current in your wire.

And I'm going to show you what to do because you're going to be making one of these soon.

So you take your iron core and you wind the wire around in some turns.

We will talk later about how many times to wind it around.

And this may look a little bit messy, but we deliberately wound the wire just around one end of the iron core.

So when you do this, try to make sure that all of the turns of wire are less than two centimetres from the end of the core.

That gives us a stronger field, actually.

If we spread the coil all the way along the core, we won't get such a strong magnetic field.

And it's helpful to twist the wire together, the end, so the coil doesn't spring apart or unravel.

If you, later, are going to change the number of turns and wind more turns onto the coil, make sure they're also close to the end.

And it's okay if you wind them on top of each other like this.

When you test your electromagnet, 'cause that's what you have now.

You have an electromagnet.

It's a magnet that's created by current going through a coil.

You can test how strong it is by bringing the coil near a pile of paper clips.

Make sure the paper clips aren't all clipped together.

They need to be separate.

Switch on the power so that you get a current in the coil.

And what you'll find now is that your electromagnet actually starts picking up paper clips.

Pick up as many as you possibly can.

This bit's quite fun.

And then, you're going to want to count them.

To do that, move your electromagnet away from that pile of paper clips that are left, switch off the current, and you will find that it drops the paper clips.

It's not acting like a magnet anymore.

And then you can count those dropped paper clips so that you know how many it could pick up.

Here's a question for you.

Why do paper clips fall off the electromagnet when the current is turned off? Is it because there's no charge in the wire, 'cause there's no field due to the coil, or because the electromagnet has reversed polarity? If you need longer than five seconds to think, press pause and then press play when you're ready.

Are you ready? Correct answer is, there's no field due to the coil.

Remember, there's a magnetic field around a current carrying wire as long as there is a current.

So you just switched off the power supply.

There's no current in the coil anymore, so there's no magnetic field, and it doesn't act like a magnet, and it doesn't attract the paper clips anymore.

Well done if you got that right.

And now it's time for the investigation.

So you're going to build your electromagnet using the instructions I showed you.

If you need to see them again, just go back to that part of the video.

And before you start collecting results, you'll need to set up a table like this one.

It shows the number of terms you're going to try and number of paper clips you're going to pick up for each number of turns.

It might look like quite a lot to do, but once you get the hang of it, you'll find it doesn't take very long to pick up the paper clips, drop them, and count them.

And when you've collected all your results, you're going to calculate a mean, an average number of paper clips picked up for each number of turns.

And you're going to plot the means on a graph.

So you'll plot number of paper clips picked up, average, on the y-axis, the vertical axis, and the number of turns on the coil, on the x-axis, horizontal axis.

Use a sharp pencil to plot each point as a cross and then draw a best fit line, and have a look at the arrangements of your points and see whether it looks like they're following roughly a straight line or whether you think you should draw a smooth curve through them instead.

And pause the video now, do the investigation, and press play when you're finished.

So here's a set of example results.

Don't expect yours to be exactly the same, they won't be.

It also depends on the size of the paper clips you used.

And if for any reason you didn't do the experiment or it didn't work out, you could take these results and draw a graph from them.

Now notice something here.

The person who did this experiment has crossed out one of their results.

And they've written, 39 paper clips for 20 turns was an anomalous result so it was not used in the average calculation.

And what's happened is they've noticed that 39 paper clips for 20 turns seems unusual.

It's really quite a lot higher than the other two results.

And we would describe that as an anomalous result, a result that doesn't fit the general pattern.

And perhaps this person made some sort of mistake when they took this measurement, perhaps they even just wrote down the number wrong.

But they've realised there's probably something wrong with it.

And so they haven't counted that result when they worked out the mean for 20 turns.

If you have any anomalous results, you should have ignored them too.

And here's an example graph.

Okay, it has five points.

They look like they're following a curve.

So the person who recorded this data has drawn a curve through them.

They've made the line go through zero, zero, because they're expecting that if there are no turns.

Well, if there are no turns, you don't actually have an electromagnet, and you're not expecting it to pick up any paper clips.

Let's go onto the next part of this lesson.

More turns on an electromagnet.

So going back to the graph, we can see that increasing the number of turns on the coil increases the number of paper clips that the coil picks up.

So the more turns there are, must be the stronger the magnetic field of the electromagnet.

So what you can see on this page is a good conclusion for this experiment.

It's what we found out.

So looking at this graph, how many paper clips would be picked up if 14 turns were used on the coil? If you need more than five seconds to think about that, press pause and press play when you're ready.

And the answer is 15.

Let's see why.

If we used 14 turns, find where on the graph we have 14 turns, and then go across to see how many paper clips that would be, and it would be 15.

So even though the experimenter didn't take a measurement for 14 turns, we can use our results to make a prediction for how many paper clips we'd be able to pick up.

It might not be exactly right, but it's probably close.

Now another question.

How many turns are needed to pick up 10 paper clips? Press pause if you need longer than five seconds.

And the answer is we would need 12 turns to pick up 10 paper clips.

Let's check why.

Go to 10 paper clips on the y-axis and go across to where that meets the graph, and then see how many turns that is on the x-axis.

Can you see that we're on 12 turns here? So we can predict that if we had 12 turns, we'd just about be able to pick up 10 paper clips.

Now a current carrying coil where you've been experimenting with, we'll have magnetic field lines actually passing through it, as shown here.

And if we increase the number of turns on the coil, we would draw more magnetic field lines inside the coil 'cause we're expecting the magnetic field to be stronger and closer together.

Field lines represent a stronger magnetic field.

Which of the following will cause a stronger magnetic field? Increasing the current, increasing the diameter of the coil, increasing the number of turns, or increasing the resistance of the coil? Press pause if you need longer than five seconds.

Well, you can increase the strength of the magnetic field of your coil by increasing the current through the coil, and by increasing the number of turns as you've seen.

I haven't said anything about increasing the diameter of the coil.

That doesn't actually strengthen the magnetic field.

And increasing the resistance of the coil wouldn't help.

In fact, it would actually reduce the current, which would reduce the magnetic field strength.

Now I'd like you to think about what you've just been doing in your experiment, and I'd like you to explain how you could make an electromagnet using, this time, an iron nail and some insulated wire and a battery.

And I'd like you to think about why the wire needs to be insulated.

I told you to use insulated wire to make your electromagnet.

Why? Take as long as you need.

Press pause.

And when you're ready, press play and I'll show you some example answers.

So here are the example answers.

To question one, how you make the electromagnet, wind the insulated wire around the end of the top of the nail.

The head will stop the coil slipping off the nail.

Don't worry if you didn't think of mentioning that.

Connect the end of the wire to the battery.

The nail will become an electromagnet.

If you want to turn off the electromagnet, break the connection to the battery, and there will no longer be a magnetic field.

Now why do we need to insulate the wire? Remember, the insulation is the plastic coating on the wire.

Current needs to flow around the coil to cause a magnetic field.

If the wire is not insulated, the current will flow straight through the wire and the core without passing through the turns of the coil.

This will not cause the strong magnetic field of an electromagnet.

There will be a small field due to the current, but not one big enough to pick up paper clips.

Did you get the key idea here, that if you don't insulate the wire, it's possible for the current to go into the core and just flow straight along the core.

So instead of getting this current that's going round and round the turns of the coil, you just get one straight line current and you don't get a strong magnetic field.

Well done if you thought of that.

Now we've come to the end of this lesson.

So here's a summary of what it was all about.

A current flowing in a wire will cause a magnetic field that can be detected with a compass around the wire.

Increasing the number of wires by coiling them will increase the magnetic field.

The magnetic field due to a coil is the same as that due to a bar magnet.

Adding a soft iron core to the centre of the coil, or increasing the number of turns on the coil, will increase the magnetic field and make an electromagnet stronger.

Well done for working through this lesson on electromagnets, and I hope you enjoyed experimenting with one.

I hope to see you again in a future lesson.

Bye for now.