# Lesson video

In progress...

Hello, everybody.

Welcome back to your fourth lesson on magnetism with me, Miss Roberts.

It's so great to see you all back here, and I've really enjoyed learning about magnets so far.

Today we're going to be really looking at how we can see an invisible field force, which you might think we won't be able to see anything that's invisible.

Well, I'm going to show you a way so that you can see something that's invisible.

Don't worry, Lenny is not sure either.

So, Lenny the lion and I already for our lesson, first of all, we're going to do a recap of our think question, and then I'll show you what resources you need.

If you wants to get your favourite Teddy to start the lesson, then pause the video and go and get them now.

So, I think question from our last lesson was this, why were campuses so helpful to people sailing in boots, no matter what the weather was like? So, I wonder what you thought about, did you have a think? Did you ask anybody about it? I hope you had a really good scientific conversation with somebody around you.

Now, I thought were this, that it would be very helpful to have a compass when sailing, because you could always find out the direction of North.

So if you were trying to travel East across the sea, then you would always know where East was because you'd have a compass facing North.

So then I know if that's North, then I can find out where East is.

It doesn't matter about the weather because companies aren't affected by the weather so that's good isn't it? I wonder what you thought.

Okay, let's get started on today's lesson.

You're going to need a pencil or pen, a ruler and a notebook or something to write with.

If you've got a magnet, then you can get it, but you don't have to have one 'cause I'm going to show you everything that you need to do under the visualizer or on the screen so you can follow along.

Pause the video and go and get the resources you need now.

Okay, so in today's lesson, we are going to do our star words.

We're going to think about what's a magnetic field is.

We're going to look at how we label field lines, then how to plot magnetic field lines.

And then I've got another thing question for you.

So, let's get started.

You know how this works and our team, star words, star words, star words.

Well done, what's the action for poles? Well done.

What's the action for field? That's a new one today.

I just wanted to put these two in here first because I haven't got friction there anymore.

So, field is going to be really, really wide arms so it's a bit like force, but that's just like that.

So field is like that with a big wide movement around your body so, can you say field like this? Your turn.

Fields like this, well done.

Now this isn't like a field of wheat or a field of poppies.

This is a field around a magnet.

That's why I want to put your arms out like this.

So let's recap our other star words.

When you plot something, you write it or sketch it.

When you plot something, you write it or well done.

Well done so those are all of our star words today.

I wonder, could you recap them yourself, because some of those words are new? Can you go through all of them now and do the actions to yourself and your favourite Teddy by your screen? So that you've got them really sticky in your mind.

Okay, so the first thing we're going to look at is something called a magnetic fields.

Can you say, magnetic field? Magnetic field.

Can you say it again? Well done, now like I've said, a magnetic field is not a big field in the countryside full of magnets because magnets don't grow from the ground or on trees.

This is the area around a magnet.

A magnetic field is the area around a magnet.

And we've learned so far in this unit that, that magnetic field is what's this word, invisible well done.

You can't see a magnetic field.

So let's have a think.

So if we can't see it at all, how do we know that it's there? The area in which an invisible force will act is known as the field of force.

Can you say field of a force? Well done.

We know that they will be a magnetic force acting between magnetic materials and a gravitational force acting between any object on the earth.

But how can we tell what size and direction this force will be acting? I've got an example for you.

The field of force around a magnet is invisible.

We can't see it, but what's I can see is when something is attracted to the magnet or what's the opposite of attract.

Oops, when it's repelled so I can feel, and I can see that magnet being repelled.

So although the magnetic field or the force is invisible, there are ways that I can see it in action.

Another example, I'm going to use Lenny the lion here to demonstrate gravity.

I can't see gravity happening, but I can do something to show what gravity and the force that's acting upon an object.

So if I have Lenny the lion and drop him, he falls to the ground.

He's okay, he's not falling very far.

So if I drop him, he falls, that's because of gravity.

And that's just like with magnetic forces, although they're invisible, there are ways that we can see that object and the magnetic forces in action.

So what is a field line? Well, field lines are where the forces are acting in the field around the magnet.

The force around the magnet will not be the same all the way around.

In some areas it will be stronger and others it will be weaker.

For example, the further away a magnet is from an object, the week of the force will attract or repel.

The closer the magnet to an object, it will be stronger to attract or repel.

So in the last unit, sorry, in the last lesson I had a magnet and I had a spoon.

This spoon was attracted to the magnet, you can see.

Now the closer the magnet is to the spoon, the more attract, the stronger the forces, but the further away you can see that the spoon is not being pulled or attracted towards the magnet this far away but the closer I get, I can feel it in my hand.

And then eventually it gets so strong that actually pulls it towards it without me even having to move it.

So, on the screen, you can see the field lines and that is the force of the magnet acting.

So as the spoon gets closer and you can see that in some areas, it's much stronger on the magnet.

Have a look at the screen, where do you think the magnet is strongest, based on what you can see on the field lines? Can you have a think and tell your screen? Well done.

On the top of the North pole and the top of the South pole, you can see that there are lots and lots and lots and lots of lines coming out.

Those are our field lines showing the force and because there's lots of them, that means the force is very, very strong.

Now have a look on where is the force weaker? Where are there fewer field lines? Can you have a thing and tell your screen? Well done, on the side of the magnet, the force lines, the field lines are further apart and they're not as condensed so they are weaker on the edge of the magnet, and also as you get further away from the magnet.

So, these field lines help us to know what force will be in a particular place in relation to the magnet.

It's a bit like a map.

The lines help us to see what's happening because it's invisible.

Now, there are ways that we can draw these.

If you use a compass, you can draw the field lines and I'm going to show you that later on in this lesson.

There's another way that you can draw the field lines and do you remember I said, I was going to show you something that's invisible? Well let me show you a picture.

The picture on the screen is of a magnet and what's around the magnet are iron filings.

Can you say iron filings.

Iron filings are basically just tiny, tiny, tiny, tiny bits of metal.

And in this case, bits of iron they're about the size of sand.

So if you can think of sand and then if you imagine that as a metal, as iron, and we know that iron is magnetic.

What they've done is they then sprinkled iron filings over the magnet.

And you can see that some of the iron filings have been very tightly attracted to the North and the South poles.

Can you point to your screen where there are most iron filings attached to the magnet? Well done, right by the North and the South pole.

Now can you point to where they are quite weak and there's not very many iron filings? Can you point to your screen? Well done, just on the edges of the magnet.

There aren't very many iron filings, so that's quite a weak force so there aren't many field lines there.

You'll also notice what shape the iron filings are in on the side of the magnet.

Can you see, it almost goes like an arc around the top and then also underneath.

Do you notice that's quite similar to the picture on the left? Well done, it is very similar, isn't it? Because on the left are the field lines and the iron filings have fallen on the field lines.

So, that's how we can see something that's invisible.

I can't see them in real life it's just a magnet, but that's what's going on in the force around the magnet.

Let's see how well you are listening.

I've got some questions for you and I'd like to answer them.

The fields of a force is an area which an, that's your clue will, and there's your blank to fill in.

I haven't given you the words this time, 'cause I want you to use your brain and if you're not sure you can go back and watch the video again, to get your answers.

Question two, a picture of field lines is like a, of an invisible force to show where a, will act in a different, around an object.

What's the two ways that you could see a magnetic field.

So, I want you to pause the video and have a go answering those questions in your notebook now.

Well done, keep going to, pause the video if you need more time, 'cause I'm going to go through the answers.

Are you ready? Question one, the field of a force is an area in which an invisible force will act.

If you've managed to get those two words correct, you can give them a tick.

If you got them wrong, that's okay.

I want you to cross them out and then write the correct answers above.

Question two, a picture of field lines is like a map of an invisible force, to show where a force will act in different positions around an object.

Some of you might written place there and that's also okay because it's the place around it, but the scientific word that could be position.

So if you've written place, I'd like to cross it out and right position, make sure you're spelling it correctly.

And question three, what are the two ways that you could see a magnetic field? You could use a compass to map the force lines or use iron filings.

And that was the two images that I just showed you in the previous slide.

Well done, everybody.

I'm going to give you an awesome cheer, because you're working so hard at this lesson so far.

So, now let's have a think about how we label field lines.

I'm going to show you a video.

Now this is a video of somebody using iron filings and a compass to show the field lines.

They start by using the compass and what they do is they take the compass and they take it next to the magnets.

And then you'll notice that using a nice pen, he draws an arrow based on where North is pointing.

This shows the force acting from the magnet and you'll see, have a watch which direction the arrows go in.

I want you to tell your screen, as soon as you see it, once he's finished doing that, he pours iron filings onto the magnet and onto the table.

Then I went to see where do the iron filings fall? Do they fall on the field lines that he's already drawn? Or did they fall somewhere different? You might have an idea already, but let's have a watch of the video and find out.

So first of all, he's going to plot the field lines.

Let's make it bigger.

So you can see he has a compass, he's putting the compass next to his magnet, and marking direction of the needle from South to North.

Then he's drawing an arrow in the direction that it's facing and pointing North.

You can see that he's going all the way along and he's connecting up his lines.

That's because all of the North and the South always connect towards each other.

You can also see the arrows are pointing, which way are they pointing? Towards the North or to the South? Can you tell your screen now? Well done, they're always pointing towards the South and they're pointing away from the North.

Can you tell your screen, where do the arrows point towards? The South and they point away from the North, well done.

What he's now going to do, is he's going to extend these lines.

He's going to plot the extra field lines, using his knowledge of magnets.

Let's see.

So those are the extra field lines.

Now let's have a watch, have a look at those iron filings and where do they fall? My question was, do they fall on the field lines or away from the field lines? Let's have a watch.

So some of them aren't attracted at all and they fall away from the magnet.

You can already see some of the iron filings are attached to the North end of the magnet, quite strongly, and also on the South end of the magnets.

Using that last image, can you see? What do you think the answer of my question is? Are they attached to the magnet on the field lines or do they fall separately? What do you think? Well done, they're falling on the field lines and you can see that lots of the iron filings are directly on those field lines.

Almost so, so, so much that you can't even see the drawings that he's done of the field lines.

So that shows you that he's done an accurate replication of the field lines.

Just before we move on, can you also see how bunched those iron filings are on the end of the pole? That's what we said before, wasn't it? That the strength of the force is strongest on the ends of the bar magnet.

Wow, I found that really interesting and I hope you did too.

What I'm now going to do, is I'm going to turn my visualizer on and we're going to do a sketch together of some field lines.

So just give me a second, I'm going to turn around my visualizer.

Here we go, okay.

So, that's my metal spoon, let's move that out of the way and here I've got my pen.

Okay so, what I'd like you to do, first of all, is draw your title magnetic field lines, and I'd like to use your nice beautiful handwriting and underline it with a ruler.

Pause the video and write your title now.

Okay, now what we're going to do is, we're going to sketch our magnetic field lines.

So based on what we already know, we're going to use that knowledge to sketch our field lines.

I've got a real magnet here that I'm going to sketch around, but if you don't have a real magnet, that's okay, you could just draw on, on your book.

So, I'm going to ask you to tell your screen lots of things so are you ready? Which direction do the arrows point? Do they point away from North or towards the North? Tell your screen now.

Well done, they point away from North.

So let's do our first ones.

They were like axe around the edge of the bar magnets.

So I'm going to do two that side, then I going to do two that side.

Always pointing away from North.

Well done.

And now what we're going to do, is we're going to do our field lines from the edges of the poles, sorry the ends of the poles.

Now, where they closer together at the ends or were they further apart? Well done, they were closer together.

So we're going to do our field lines away from North, and we're going to have them really close together.

So you're going to do lots of small lines around like that, and same with the South.

So remember they're pointing towards the South.

So I'm going to have lots of them pointing in towards the South.

Wants to make them nice and bunched up 'cause I know that that's where the force is strongest so I really want to show that.

So now what I can do is I can connect some more field lines around the edge of my magnet.

There we go.

Okay, if you've gone along with me, that's brilliant you can pause the video and finish your diagram, or you can pause the video now and complete your field line sketch.

Have a go, off you go team.

Okay, what we're now going to do is I'm just going to show you how we can plot our field lines.

So, let me turn my visualise a back round, whilst I'm doing that, what I'd like you to do is write your title, your new title of plotting magnetic field lines.

You also need to go and get your compass if you've got one, if not, you can just watch me having a go.

So, that was our magnetic field lines and our sketch.

Now we're going to look at how we plot them.

In order to do this, we use a compass, a magnet, and a pencil.

And this is what we looked at in the video of the man plotting with his pen.

So, let's have a go.

If you don't have a compass that's okay.

You can just watch me have a go.

So let me turn back to my visualizer and then we'll get started.

So, plotting magnetic field lines, I use my magnets.

Now this time it's really important that you use a magnet if you've got one, because otherwise it's not going to be magnetic if you just draw a magnet.

So if you don't have the resources, don't panic team, you can just watch me.

So here, I've got my compass.

And like we've said before, this compass is in water and it's magnetic inside the small pin, which means that it always points to North.

However, do you remember last lesson we said, that if it's near a magnet, it's going to point differently.

So now you can already see that North is now incorrect, that's not where geographical or the magnetic North of the earth is.

It's being affected by the magnet so this North is being attracted or repelled by my magnet.

What do you think, can you tell your screen? Well done, it's being repelled because we remember that opposites attract so the North must be repelled by the other North.

So, I can see that the South is starting, oops it's got this.

In fact, I'm just going to draw a line so I don't use my compass and I'm going to use a pen so you can actually see it.

So I can see my South is pointing from there and I can see my North is pointing up to that.

So I'm going to draw a dot and then I'm just going to move that, and I'm going to connect my lines there like that.

And then I'm going to touch it again.

So that's where my South is and that's where my North is ending, so it comes round like that.

So let's try this side.

So let me show you that once more.

So, you can see that South is right on the edge of my magnet here it's right in the corner.

Start where it's starting and then I'm plotting where it's fixed, sorry, let me move my finger.

Plotting where it's pointing to North so that's where it's pointing to North.

So that's where I want to make a mark, so that I can then connect my arrow.

And that's where it's pointing towards so I put my arrow on there as well.

Then I'm going to get South again and I'm going to line it up.

Oops, let's get the magnet in the same place, line it up with the end of my arrow underneath which I can see us there, and then my North is pointing here so I'm going to connect it up again like that, okay? So, then around the edge, on the edge of my magnet, I can see that North is pointing towards the magnet.

So North is actually facing towards the South pole of my magnet because it's being attracted so that's where South starts.

Let's see when North and it's just here.

So I can plot the field lines of my market because the North of my compass is always being attracted to the South of my magnets.

That's amazing, isn't it team? So that's plot my South and plot my North and draw my line.

Let's do it again, so South, oops, make sure that's in the same place.

South is here, North is here and I'm plotting my line, okay? Let's do it from the top side now as well.

So the South of side of the magnet is now being attracted to the North, sorry of the compass is being attracted to the North side of the magnet.

Like to get those muddled into it, that's my South and whereas they connects to the North over here.

So it's coming in like that, this is so cool.

That's my South and that's my North pointing up here.

Now I've got quite a compass in compass because it's used for hiking, but you can still see where the North and the South are pointing to.

Let me just show you under the visualizer.

You can see that I've even got a magnifying glass on it, but for plotting lines on a magnet, it's not the best 'cause it's not the smallest.

You want a small one so that you can get all of those lines.

Oops, I just realised I've made a mistake.

What mistake have I made team? Have a look at my diagram, what have I done with my arrows? Can you tell to your screen which way is those arrows should be? Well done, you've spotted by mistake.

But that's okay, it's okay to make mistakes.

'Cause I've just realised that I've been pointing my arrows where the South side of the compass is But I've told you all lessons that they need to be facing where the North side is, so it's actually pointing away.

So I'm going to cross those out and point my arrows the correct direction.

I also know that they should be pointing away from North so that makes sense, but that's okay even teachers make mistakes team.

Just do my final one in here, so that's pointing outwards like that and there we go so, those are my initial field sketches.

I could also do some wider ones around here.

Let me just show you, if I start from South again over here, plot my North here.

It comes all the way out quite far.

So let's see where this goes, if I put myself against it, my North ends up over here, South connects around like this.

Let's see, is it going to, you can see my South connects to my arrow and my North is being attracted over here.

It's interesting here team that my South is here, my North doesn't go directly in to my magnet so it doesn't go in across like this.

You can see that this is a really good example of realising that the end of this magnet is strongest.

So the force actually wants to come round and get to the nice sweet spot, which is the end of the market, not just the side.

So let me keep plotting this.

So there's my south, there's my North, plot that round like that, let's do one more attached my South whereas my North end up over here wants to get really to the end of that magnet, doesn't it? Let's do one more so it's nice and even.

So, that's coming on this side, so I'm touching my South over here, and my North comes all the way around this side, and it's a bit further away trying to be as accurate as I can using the resources I've got.

So I've got my North round here, making sure not to make that same mistake twice if the arrow is going in the right direction, that's my South pole against my arrow.

My North every time it's always really finding the strength that magnet, and it really wants to find the end of it so where's my South pole? There we are.

And there we go.

So I have now plotted some field lines around my magnet using a compass.

I hope you enjoyed watching me.

If you do have a compass and a magnet, you can have a goat that yourself.

And you can pause the video in order to do so.

Okay, so let me do that, in fact I'm going to do that and then I'm going to turn my visualise around so you can see me again.

I'm going to explain what happens next.

So pause the video if you need more time to have a go that or if not, then you can carry on watching 'cause I'm going to show you something really cool.

This is something called ferrofluid.

And this is something I find absolutely fascinating.

We've talked a lot about magnetic materials and objects that are solid, but this ferrofluid is a magnetic liquid.

Isn't that so cool? I'm going to show you a short video of this liquid.

So inside the jar is a thick black liquid and this is magnetic and you'll see why, because on the edge of the glass, they hold a magnet.

And you can see that the liquid, the thorough fluid is attracted to the magnet.

So let's have a look at what happens.

So you can see that fluid is being attracted to that magnet on the edge of the glass.

And then when the magnet's released, the fluid goes back and attaches to the magnetic iron pole that it's attached to in the middle.

Isn't that fascinating? So, we're going to watch that one more time.

So what's happening is there's a magnetic fluid that's attached to a magnet inside the glass.

Then another magnet is brought near on the outside of the glass and the ferrofluid is attracted to it, so it scoots right to the edge and really wants to be attached to that magnet.

Let's have a look.

So there it is.

And then the magnet is attracting the ferrofluid inside when it's released, it then goes back to its state inside the glass.

Isn't that fascinating? There are so many things that you could use that for.

Wow, to be a scientist gracious me.

Okay, so, that is the end of our lesson today team.

The final thing to do is think about, all think question, How do we know the force of magnetism exists, if we can't even see it? Oh gosh, I feel like today my mind is blown by lots of things do with magnetism because it's invisible and it acts in a way that we can't see.