 In this video, we're going to be going over how the hysteresis loop is formed, and what we mean by this hysteresis loop, it's a characteristic of, say, some sort of metal as to its retention of magnetism. So whether it retains magnetism or not, and so we're just going to walk through this and hopefully you'll get a better understanding of exactly how this all kind of plays together. So what we have here is we have an x-axis and a y-axis. Our x-axis is labeled H, and what that means is magnetizing force. What magnetizing force is, the force needed to create flux lines. Our y-axis here, you notice, has the B, which is our flux lines, it's Tesla. So how many flux lines are being created? This little line here is our magnetizing curve. So what happens here is if you can see, as we increase our magnetizing force in, say, some sort of iron core or steel core, it could be any kind of metal, then you're going to see that the flux lines increase. So again, we're talking about a wire wrapped around a core. So we're basically creating an electromagnet. So this, as we increase our magnetizing force, then our flux lines increase until they get to a certain point. And that point is called our point of saturation, which means that no matter how much magnetizing force you can put on this, if we keep increasing it, you can't put any more flux lines into that piece of metal. Because it gets to a point where it's like the toothpicks, when you're putting toothpicks into the little toothpick bottle, it gets to a point where it's all full. And so we hit saturation. So we're going to see what happens. When we do that, we magnetize it. And then if we get rid of our magnetizing force, let's see what happens to this. As we get rid of our magnetizing force, so our magnetizing force goes back to zero, you'll notice that it retains some flux lines. This doesn't just drop out like that. What happens is the flux lines, there are some that retain or stay. So that might not be a good thing. You might want to get rid of those flux lines. So what we call this though is our point of retentivity or retention, which we're going to denote with that R. Now if we want to get rid of this, what we have to do is put a magnetizing intensity on it in the opposite direction. So we gave it a positive magnetizing force, which created this magnetic line here. And then to hit saturation, we turned it off. It went back here. We still have some retaining of magnetism here. So in order to get rid of it, we push it the other way, which could drop our flux lines down to zero. Now we call that coercive force, which we're going to denote with the C here. Now if we somehow just kept this magnetizing force going, it ends up creating another line like this, but an inverse line in this direction. So you see that it keeps going, going, going until it hits that saturation point again, but in the opposite direction. And then the same thing follows true. So it's going in the opposite direction. Then we realize that we've left the magnetizing force on in the opposite direction. If we turn that off, what should happen, it should be the inverse of what happened up here. So we should see it drop back and retain some magnetism, but in the opposite direction. Which is exactly what has happened here. So we've retained some magnetic lines of force in the structure itself, but in the opposite of direction of what they were there. So again, in order to get rid of this, we're going to have to coerce it into the other direction. Now before we do that, we have to note that it is retained here as well. So we had retention up on the positive side and we have retention on the bottom as well. Then we are going to coerce it back. So we put some more magnetic intensity on it in the opposite direction and we can get rid of all those flux lines. We end up with a flux of zero at this point too. And again, if we left the magnetizing force on in that direction, it would continue to go. So again, we had to coerce it. So this is our course of force at this point here, which we can see with the big C. So again, if we were not paying attention and we left our magnetizing force on, what's going to happen is it's going to go in this direction again and still hit saturation and see what happens here. And we can see that it goes back and hits that point again of saturation and the whole thing continues again. So what we end up with is what's called the hysteresis loop. Now when we have cores that have a skinny hysteresis loop, meaning that when we let go of this and it goes back down close to zero, that is something that does not retain a lot of electromagnetism, which is something that would be good for, say, like a transformer or a coil because you don't want it to retain that magnetism. Whereas if you're trying to create a big huge electromagnet, you want to have it kind of come up top here. So what we talk about is how a hysteresis loop for an electromagnet, something that you want to have retain its magnetism, is going to be relatively large or fat compared to if you have an iron core or something for a transformer or a relay or a coil, you want that to be skinny. So it's going to kind of, as soon as you get rid of the magnetic intensity, that it's going to drop down closer to zero. So that's kind of the basic walkthrough of how a hysteresis loop is formed. And as always, if you have any more questions about this, we're going to be focusing a bit more on magnetism for a little bit because you cannot have electricity without magnetism and the two always go hand in hand. So I think it's important that we have a good grasp of magnetism.