Welcome to another Unisur Physics Vodcast. Today I'll be exploring the magnetic fields of simple coils using three magnetic field demonstrations and visualising a two-dimensional slice through each configuration. Each demonstration has a hollow square acrylic plate that has been filled with a clear light low viscosity oil and a small amount of iron powder. So you can see here these dark bits. Mounted through each plate, coils of enameled insulated copper wire arranged in three different types of configurations. We will shake up the oil and evenly disperse the iron powder, then connect the coils to a low voltage power supply, approximately two volts and a current of about five amps will flow. The iron powder will align itself with the magnetic field lines allowing us to visualise the otherwise invisible magnetic field. Okay, well let's take a look at each of the coil configurations. Let's look at this one first. As we can see there's a green plastic former here. What that's to do is to actually hold the coils of copper wire. There's approximately fifteen coils of enameled copper wire here. They loop around, they go straight through the plate in the centre there and you can see that the two ends of the coil are terminated on these posts here. Okay, this one here actually just a simple coil. There's fifteen turns of wire on that and you can see the two wires coming down there and they're terminated on these posts here. And lucky last, this one's actually got five coils and on these former's is actually fifteen turns of copper wire on each and if we look carefully on the bottom here we'll see that the wire starts on this post here, comes up onto the coil, fifteen turns and it loops across onto the next one, fifteen turns, runs down to the end there and the other end of the wire is terminated on that post there. So let's shake them all up, get behind, power to evenly disperse and then we'll connect it up to the power supply and see what we get. This one's the hardest one to shake up. You'll see that it gets funny patterns in it. Okay, and this one's the easiest one because there's lots of things through it that stirs it up really quickly. Okay, so let's look at the centre one first. So we'll need to connect it up. So we'll just connect the alligator clips to the posts. That's actually connected to a little Morse code tapping key which when I press it the current flows and that's just sitting off to the side and I think we'll zoom in a little bit so I can see what's happening. It'll probably do and we'll start the current flowing. Now I just press it down for a short period of time just a few seconds because we've got around five amps flowing and this copper wire is fairly thin and it warms up pretty quickly. So just a few seconds each time I press down the Morse code tap a key. Okay, so we can see something happened there. We're starting to get the iron powder start to form circles around that wire. Sit down again for a little bit. And again, okay, not much is happening so we'll stop there and let's examine what we've actually got. So we can see that the iron powder further out is still pretty evenly dispersed as we move in closer. We start to see it forms circles around the copper wire that's running through the center there. So what's this actually indicating? We've got a current flowing down through the acrylic plate and the iron powder there is going to align with the magnetic field lines. So what we can see is that the magnetic field lines are actually around the coil that's going through the plate. Okay, that's pretty interesting. Let's look at another one. We'll just disconnect the terminals off there. I'll put this off to the side so we can have a look at it at the end. We'll have a look at the coil of copper wire. There's about 15 turns on this. I'll connect up the terminals. Okay, probably zoom in a little closer on this one. And we'll press the Morse code tap a key and see what happens. Here we go. Oh wow! Okay, I'll just press it again. Okay, let's see what's happened. Well, we can see that the iron powder is lined up down the center here. And then we're still getting this sort of circular shape around. Let's just have a look at what it looks like. It's going through the plate there. And we're starting to get some circular shapes, especially up close. You can see that it's forming circles and then it's sort of an offset circle here and on the other side. So what's this indicating? So magnetic field lines are straight down the center and then it's starting to curve off and then start to form circles close and these ones are running out. And then we've got this evenly distributed powder at the edges. Okay, well let's look at the third one. Let's see what that looks like. Let's just disconnect the... I'll bring in this coil. We'll zoom out a little bit. Just remember what this one looks like. It was a set of five coils and each one of these has about 15 turns on it. Now it's a little bit dark so I've got a light source on the side here. I'll just bring it in a little bit closer. It brings up the contrast. You'll connect the power supply to the terminals. And okay, we'll press the more tapestry and see what happens. Okay, so we can see the down the center here we've got the iron powder lining up and it's curving at the edges. Let's zoom in a little bit closer. I'll just move a demonstration around so we can have a look at what's happening. So we can see some detail there. We can see that the it's curving right around this end and then as it goes along the coils it seems to go in and out. Right along the edge there. At the other end, still getting a bit of looping around the edge here but it's not joining up. Okay, so we'll zoom back out. Just have a quick look at all the displays again. So our five coils. We can compare that to the single coil and there's some definite similarities there. It's got through the center of the coils. We have them lining up and the curvature at the ends, but it's just happening at the ends and something different is happening along the edge there. And then just have a look at the first one we looked at, which was the big square coil. And we can see that this one's actually forming a large circle around here. And then if we do look carefully on this we can see that down through the center of the coil they are actually lining up a little straighter here. Okay, well I hope you enjoyed these three magnetic field demonstrations and I look forward to chatting with you again in another Unisur physics podcast.