 So far we've covered the magnetic forces on individual charged particles that are moving through magnetic fields. And if you need to go back and review those concepts, watch those videos and look at your lecture notes again. But now let's talk about a very, very particular type of charged particle that's moving, a current, and a current flowing through a wire. Well if we start from the conceptual view, we're actually going to take a look back here at our equation for electrons moving in a magnetic field. And remember our general equation was that the charge multiplied by the cross product between the velocity and the magnetic field gave us the force of the particle. And we could do that using the cross product or we could use our right hand rule. But because our charge on electrons was a negative charge, the force was the opposite direction from our typical right hand rule palm of the hand. So it's kind of like you use the back of the hand to give you the direction on the electrons. Now if it's really in a free region of space, when I start my electron off, its force is always perpendicular to it, but that causes it to change its direction, which causes it to change the direction of the force causing us to move in circular motion. We had a whole lecture looking at that. So if it was in a free region of space, then the electron would tend to move in a circular path. But electrons that are in wires aren't free to move in a circular path, they're stuck inside the wire. So let's think about these charges that aren't free for the charges that are in a wire. Well, I've got two types of charges. I've got the protons and they don't move. And because they don't move, we don't expect any kind of magnetic field. And then we've got the electrons. Now the electrons are stuck inside the wire. So they could move to the left or to the right, but they can't just move in circular motion. They're not going to be allowed to move up or down because they're stuck inside this wire. So we don't have the same sort of motion that we have, but we still have forces that are acting on them. Let's take a look at this in a little bit more detail using an example. Okay, so imagine that we've got a region of space where we have a magnetic field pointing into the board. And remember, into the board is given by these little X's because you're looking at the back side of the arrow. And let's say that we've got a current which is flowing off here towards the right. First thing we want to remember is that just because our current is flowing towards the right, that's not the direction the electrons are flowing. The electrons are negatively charged particles that are moving in the negative direction. And so that gave us our direction for the individual electrons. Now if I use my right hand rule on this, my fingers would be pointing into the board or into the screen. My thumb would be pointed off to the left. My palm is facing downwards, but since these are negative charges, it's the top of the hand that gives us the direction, the force. And that means the individual electrons feel a force upwards. They're not free to move upwards, but they feel a force that's upwards. And it's not just one electron that this is happening to. It's every electron in the entire wire. So the net effect is all these electrons that are moving through the wire create a net force that pulls not on the individual electrons moving them off course, but pulls on the wire itself moving it upwards. So conceptually, we expect a force on a current carrying wire in a magnetic field. We still need to get the equation for that, and that's going to be our next video clip.