Learn about Magnetism 11: Electric Motors Video

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Learn about Magnetism 11: Electric Motors

So where I had left off is we had this circuit, we had these little leads here. This was kind of our innovation. And this is actually called a commutator, where this part that’s connected to our rotating piece, that’s the commutator. And these are the brushes, so they kind of, you could imagine you could design as brushes that always stay in touch. Kind of like the brushes on a, what was that? What are those cars at the amusement park? Bumper cars, right? On the bumper cars, you have a pole behind your bumper car, I’ll draw that for fun, so let’s say this is your bumper car, looks like a shoe a little bit. This is you driving your bumper car. They have a pole, and at the top of the pole you’ll see these brushes that are touching the ceiling, right? You could view that as the same type of brush. So what it allows is a constant electric current to flow through the ceiling. I’m assuming, I don’t know what direction it’s going in but it allows a current to flow through the ceiling and maybe your car is grounded so the current can flow down to the ground. So that your car could be powered by the ceiling and not have to carry a battery in every car which would be kind of a waste of energy and probably some type of a health hazard and safety risk et cetera, et cetera.. So those brushes on your bumper cars are not to, might not be all that different from the brushes that are touching the commutators here, just a little bit of terminology. And, never hurts to introduce bumper car references. Probably should have done them earlier when we’re learning about momentum and things. But anyway, so what was happening here? So going back to our first video, we have the current going down like this. And then if you use your right hand rule with the cross product, you know that the net force from the magnetic field is going to be downwards on the left hand side, upward on the right hand side. So you have a net torque rotating it like that. Rotating the right out of the page, the left into the page or into the video screen, up to the point that you’ve rotated 90 degrees. And now you’re looking kind of, so this side right here, let me do it in a different kind of color so you could see it. This side, is this side. Right on top. And this side is on bottom, below the page. This side is now above the page, right? If this distance is R, this side is now R units above the page. And I said, ideally maybe your commutator loses touch with the brushes at this point right? Because they’re popping out a little bit. So when you’re vertical that you lose touch with the brushes. So you have no circuit flowing. so you save a little battery energy and you just let a little of the angular momentum carry this whole rotating contraption further a little bit to the point that your configuration will look like this. Well the whole contraption will now look like this. Okay, that’s my positive, negative, positive, negative, current flows like this. Now we assume that the commutator has gotten back in touch and I just want to, let me, color code this. So if this side is this color, right? Then this side, now this is what we’re looking at top on where it’s popping out of the screen, where it’s above the screen. And now we’ve rotate a hundred eighty degrees, and this side is on this side, right? And if this side, let me pick a suitable color, if this side was green. Now this side, we flipped the whole thing over a hundred and eighty degrees. Now something interesting happens. Remember, before we had this commutator and everything if we only just flipped it over the current. Because before when we didn’t have the commutators, the current here was flowing down here, up here. And before the commutator, we had the current flowing down here and up here. And so we were switching directions. And so we would have had this thing that would never completely rotate, it would just keep flipping over, right? Which may be useful for I don’t know, if you wanted to flip things. But it’s not useful as a motor. So what happens here? Now this side, all of a sudden instead of being connected to this lead is now connected to this lead and this green side is now connected to this lead. So something interesting happens. now the current on the left side is still flowing down, right? And the current on the right side is still flowing up. So we’re back to this configuration except that this contraption has flipped over. The brown side is now on the left and the green side is now on the right. And, what that allows is that those net torques are still going in that same rotational direction. Use your right hand rule. The current is flowing down here, so if your magnetic field is coming to the left. Then the net force is going to be down there and it’s going to be up there. And so we can continue and we solved our other problem that we will never keep twisting these wires here. So now, using the commutator, we have essentially created an electric motor. And remember I drew that little thing that could be like the axle maybe, that turns the wheels or something. So if you have a constant magnetic field and you just, by using this commutator, which as soon as you get to that kind of vertical point it cuts the current. And then when you go a little bit past vertical, a little bit past 90 degrees, it switches the direction of the current. So on the left hand side, you always have the current coming down. And on the right hand side you always have the current going up. So that the net torque is always going to be pushing, is always going to be rotating this contraption down on the left hand side and up on the right hand side. Coming out of the page on the right hand side and then down on the left hand side. And you could actually turn a wheel now. You could create an electric car. So that is the basics really of how electric motors are created. Well there is another way you could try you didn’t have to use a commutator. One methodology you could have used is, you could have had the magnetic field going until you get to this point. And then you turn off the magnetic field, right? And maybe you wait for this situation to go all the way a hundred and eighty degrees and then you turn the magnetic field back on again. Right, that’s one possibility. But that’s, you know, maybe not as efficient because half of the because half of the cycle you’re not powering it or, maybe you switched the direction of magnetic field, or another option you don’t have to use a commutator maybe you use some other contraption to switch the direction of magnetic field. But this is probably the simplest way to do it and I think it gives you a general idea of how an electric motor can be created and then we could play around with the mechanics of innovations on it. But all electric motors are essentially some variation of what you have learned in this video. Isn’t it neat to learn something useful? See you in the next video.

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So where I had left off is we had this circuit, we had these little leads here. This was kind of our innovation. And this is actually called a commutator, where this part that’s connected to our rotating piece, that’s the commutator. And these are the brushes, so they kind of, you could imagine you could design as brushes that always stay in touch. Kind of like the brushes on a, what was that? What are those cars at the amusement park? Bumper cars, right? On the bumper cars, you have a pole behind your bumper car, I’ll draw that for fun, so let’s say this is your bumper car, looks like a shoe a little bit. This is you driving your bumper car. They have a pole, and at the top of the pole you’ll see these brushes that are touching the ceiling, right? You could view that as the same type of brush. So what it allows is a constant electric current to flow through the ceiling. I’m assuming, I don’t know what direction it’s going in but it allows a current to flow through the ceiling and maybe your car is grounded so the current can flow down to the ground. So that your car could be powered by the ceiling and not have to carry a battery in every car which would be kind of a waste of energy and probably some type of a health hazard and safety risk et cetera, et cetera..
So those brushes on your bumper cars are not to, might not be all that different from the brushes that are touching the commutators here, just a little bit of terminology. And, never hurts to introduce bumper car references. Probably should have done them earlier when we’re learning about momentum and things.
But anyway, so what was happening here? So going back to our first video, we have the current going down like this. And then if you use your right hand rule with the cross product, you know that the net force from the magnetic field is going to be downwards on the left hand side, upward on the right hand side. So you have a net torque rotating it like that. Rotating the right out of the page, the left into the page or into the video screen, up to the point that you’ve rotated 90 degrees. And now you’re looking kind of, so this side right here, let me do it in a different kind of color so you could see it. This side, is this side. Right on top. And this side is on bottom, below the page. This side is now above the page, right? If this distance is R, this side is now R units above the page.
And I said, ideally maybe your commutator loses touch with the brushes at this point right? Because they’re popping out a little bit. So when you’re vertical that you lose touch with the brushes. So you have no circuit flowing. so you save a little battery energy and you just let a little of the angular momentum carry this whole rotating contraption further a little bit to the point that your configuration will look like this. Well the whole contraption will now look like this. Okay, that’s my positive, negative, positive, negative, current flows like this.
Now we assume that the commutator has gotten back in touch and I just want to, let me, color code this. So if this side is this color, right? Then this side, now this is what we’re looking at top on where it’s popping out of the screen, where it’s above the screen. And now we’ve rotate a hundred eighty degrees, and this side is on this side, right? And if this side, let me pick a suitable color, if this side was green. Now this side, we flipped the whole thing over a hundred and eighty degrees. Now something interesting happens. Remember, before we had this commutator and everything if we only just flipped it over the current. Because before when we didn’t have the commutators, the current here was flowing down here, up here. And before the commutator, we had the current flowing down here and up here. And so we were switching directions. And so we would have had this thing that would never completely rotate, it would just keep flipping over, right? Which may be useful for I don’t know, if you wanted to flip things. But it’s not useful as a motor. So what happens here? Now this side, all of a sudden instead of being connected to this lead is now connected to this lead and this green side is now connected to this lead. So something interesting happens. now the current on the left side is still flowing down, right? And the current on the right side is still flowing up. So we’re back to this configuration except that this contraption has flipped over. The brown side is now on the left and the green side is now on the right. And, what that allows is that those net torques are still going in that same rotational direction. Use your right hand rule. The current is flowing down here, so if your magnetic field is coming to the left. Then the net force is going to be down there and it’s going to be up there. And so we can continue and we solved our other problem that we will never keep twisting these wires here.
So now, using the commutator, we have essentially created an electric motor. And remember I drew that little thing that could be like the axle maybe, that turns the wheels or something. So if you have a constant magnetic field and you just, by using this commutator, which as soon as you get to that kind of vertical point it cuts the current. And then when you go a little bit past vertical, a little bit past 90 degrees, it switches the direction of the current. So on the left hand side, you always have the current coming down. And on the right hand side you always have the current going up. So that the net torque is always going to be pushing, is always going to be rotating this contraption down on the left hand side and up on the right hand side. Coming out of the page on the right hand side and then down on the left hand side. And you could actually turn a wheel now. You could create an electric car. So that is the basics really of how electric motors are created. Well there is another way you could try you didn’t have to use a commutator.
One methodology you could have used is, you could have had the magnetic field going until you get to this point. And then you turn off the magnetic field, right? And maybe you wait for this situation to go all the way a hundred and eighty degrees and then you turn the magnetic field back on again. Right, that’s one possibility. But that’s, you know, maybe not as efficient because half of the because half of the cycle you’re not powering it or, maybe you switched the direction of magnetic field, or another option you don’t have to use a commutator maybe you use some other contraption to switch the direction of magnetic field. But this is probably the simplest way to do it and I think it gives you a general idea of how an electric motor can be created and then we could play around with the mechanics of innovations on it. But all electric motors are essentially some variation of what you have learned in this video. Isn’t it neat to learn something useful? See you in the next video.

Transcription by: Scribe4you Transcription Services