12.4 3rd Hand Rule - Moving Charges

Right, in this lesson, we're going to look at what happens now when we have a charge that's moving. So our first and second hand rules were when we had a wire with some sort of charges moving through it and then we got a magnetic field going around it. As we said, the magnetic field lines were circular, going around that moving current or if the current was round, then our magnetic field was in a row. That was our first rule, that was our second hand rule. So now today, what we're going to look at is what happens a little bit more in detail, and we're going to be a third-hand rule. So if a current moving creates a magnetic field, then that means that there should be some sort of magnetic force. So, if you have a charge or a wire or anything moving through a magnetic field, there's going to be some sort of force acting on it. So today, we're going to figure out how to figure. To figure out the direction and calculation of the force, let's first look at a wire in a magnetic field. In the first diagram, we can see a current running through the wire. The second picture below provides a two-dimensional view, which may make it easier to understand. The magnetic field, represented by the symbol "B," is shown as pointing to the right. The current in the wire is depicted as going into the page. To determine the force, we can use our thumb to indicate the current direction. In this case, our thumb points into the page. Our fingers point towards the magnetic field, and in this scenario, our palm would face upwards. This upward direction represents the magnetic force. In class, I will demonstrate this using three fingers. You can use your index finger to indicate the direction of the magnetic field, and your thumb to determine the current direction. Pointer finger, we measure B, and then your F finger is your middle finger. In it, make sure all three of them are perpendicular to each other, and that'll be a good way to figure out the direction of the force. The formula that we use has two different formulas depending on the scenario. The first one is I = BLSinθ, where I is current, L is the length of the wire, and B is the magnetic field. On your formula sheet, they don't write it as Sinθ, they write it as ILB, and they say that it has to be perpendicular. As long as it's perpendicular, that means it's 90 degrees. Sin of 90 would be 1, so it doesn't do anything different. The only reason we use the Sinθ is sometimes instead of it being perpendicular, maybe it's gonna run at a bit of an angle. If that angle is 60... Degrees, the sine of that angle would actually give us the perpendicular component. So, it'll work either way, but most times you don't have to worry about that 90 degrees. So, this first example is asking you to calculate the current and the wire with all of this. So, in this one, we do have a PC angle because it's at an angle. So, we would have:- Force: 1.887 Newtons- Current (what we're looking for): ?- H: 3.45- B: 1.29- Angle: 67 degrees If we rearrange that equation and solve it for i, we will get 0.46 amps. Before, current was just measuring how much charge is moving per second. Okay, so let's put in force example. Now, Part B is asking, "Well, how much charge is that in 7.1 seconds?" On your formula sheet, there's a Q/T formula, so we put in 0.46 equals our charge (which is what we're looking for) divided by 7.1 seconds. We just multiply those and we would get approximately 3.3 coulombs of charge. And then, if we wanted to know how many electrons, we could still do that. We just divide it by 1.1819, and that will tell us how many electrons flow. So, Part B was pretty easy, and they just add-ons to most types of questions. So, that was if we have a wire moving through a magnetic field, we get a force on it. But we can also use the same hand rule and just use a different formula if we just have a charge. So if you have a single charge, we use Q for the charge and V for the velocity instead of current. And we use B for the magnetic field. Once again, we have sine theta if needed, just because it could be at an angle. But in most cases, it won't be. For this one, it says we're at a perpendicular angle, so our sine of the angle would be 90, and we don't need to worry about it. So we just want to use QVB. We have an alpha particle, so that charge would be 3.2 x 10^-19, velocity is 1.22 x 10^4, and our B was 23. We just need to multiply all three of those together, and we get an answer of 9 x 10^-14 Newtons. Okay, so it's a pretty easy formula to work with. Hi everyone! I'll be your key BB. They both work, you know, pretty much the same. And the key idea then is to use your left hand for Negative charges (left hand) attract positive charges (right hand) to help you figure out the directions. That's all.