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Current time:0:00Total duration:6:40

Video transcript

so where I had left off as we had this circuit we had these little leads here this was kind of our innovation and this is actually called a commutator where these this part that's connected to our rotating piece that's the commutator and these are the brushes so they kind of you can imagine you could design them as brushes that always stay in touch kind of like the brushes on a a on a what was that a 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 and 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 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 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 etc etc so those brushes on your bumper cars are not - might not be all that different from the brushes that are the brushes that are touching the commutator is here just a little bit of terminology and never hurts to introduce bumper car references probably should have done them earlier when you'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 different color so you can 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 our units above the page and I said ideally maybe your your commutator loses touch with the brushes at this point right because it popping out a little bit so when you're vertical they actually lose touch with the brushes so you have no you have no circuit flowing so you save a little battery energy and you just let a little bit of the angular momentum carry the whole this whole rotating contraption further a little bit to the point that you are your configuration will look like this so I know I keep changing colors foot or the whole contraption will now look like this well now 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 let me color code this so if this side is this color right then this side now this is when we're looking at top on where it's popping out of the screen where it's above the screen and now we've rotated 180 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 180 degrees now something interesting happens remember before we had this commutator and everything if we just flipped it over the current because before when we didn't have the commutator the current here was was flowing up was flowing down here up here and before the commutator we had the flat current flowing down here and up here and so we were switching directions and so you 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 inside instead of being connected to this lead is now connected to this lead and this green side is now collected 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 torx 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 indefinite ATAR 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 turn it cuts the current and then when you go a little bit past vertical a little bit past ninety 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 you know turn a wheel now you could create an electric car so that is the basics really of how electric motors are created I mean what most electric well there's another way you could have done you didn't have to use the 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 the this situation to go all the way 180 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 cycle you're not powering or maybe you switch 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 a magnetic field but this is probably the simplest way to do it and I think it gives you a a general idea of how I'm at 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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