 So we had just finished example six. We've done our right hand solenoid rule and now we come to the toughest one It's called the right hand motor rule and this is why you can't bring magnets near electronic devices Here it is as it turns out If you have a moving charge It will get deflected by a magnetic field The magnetic field will exert a force on it and the easiest way to get moving charges is to contain them in a wire In fact, we call that current Leslie. So here we have a battery right there and We have a wire carrying current based on that battery. Which way is the current in this wire left or right? Which way is the current in this wire to the left or to the right for the right and then here's an external Magnetic field. So this is not the magnetic field generated by the wire itself This wire has been humming along nicely, but then there's an external magnetic field Which way is this magnetic field? What does that symbol mean? Do you remember? Okay out of page as it turns out This magnetic field will exert a force on the moving charges within the wire and I'll show you Should I have this open already? I think I did and I closed it accidentally Okay, so it's from MIT and here's the setup We have a 12 volt battery We have an on-off switch a long wire and a Strong magnet. So what we have right now is a wire and an external magnetic field now right now They haven't turned on the current yet. So right now there are no moving charges right now There is no force watch what happens when we turn on the current Very noticeable. Oh, and if we reverse the current so which way was the force this time what direction? Which way did the wire jump up? What do you think would happen if we reverse the current? Which way would the force be? Oh, let's find out. Yeah fact enough to cause the whole thing to collapse The real question is this how the heck can I figure out the direction of the current? This is the toughest right-hand rule. So here we have a current moving to the right I'd like all of you to pick your papers up so they're 90 degrees vertical so that they basically match my screen behind me Yes, we're doing this lesson now Point your right thumb in the direction of the current like this Which way is the magnetic field? What are those dots mean? Which way is the external magnetic field? What are those dots mean? Which way is the external you guys answered this 30 seconds ago? Okay out of the page extend your fingers so they're pointing out of the page now You're gonna have to bend your hand crooked like this a little bit. Sorry Okay Your palm points in the direction of the force this wire would get forced down the page Now honestly what I would do to do this particular diagram is probably just do that The leisure we'll see So here's what it says It's called the right-hand motor rule. It's called the right-hand motor rule because this is also what explains how an electric motor will work You point your thumb in the direction of the conventional current You extend your fingers in the direction of the magnetic field your palm pushes in The direction of the net force so in the above example, what would the net force be? down the Page and look So you have your math binder here, okay You know where it might be or do you need the lesson again? You want a copy of the lesson or yes, okay? Sorry for those of you at home. So let's look at example seven. This is my really quick sketch I don't do these very artistically. Sorry So here we have the current going which way into the page Right, which way is the external magnetic field the big magnet like we saw in the video? What direction To the left, okay, so you ready which way would this wire will experience a force which way point your thumb into the page Now I started to go like this I started to try and bend my fingers my fingers extend your fingers in the direction magnetic field and then let's say I got Clever and I said why don't just put it here It's way easier to be flexible. You may need find it easier to move your hand across your body Trust me thumb into the page fingers this way which way is my palm pointing with respect to the page up the page This wire would get deflected the Page I'm gonna stand up for the next couple because I could see a few of you I was being screened by my tablet because I'm recording less than I'm trying to get thick at my voice But such as life will be okay Can you get out the right hand rule questions sheet that I also handed out last day? Okay, and you want to find question number two now question number two The number two appears on the first half page, but the question itself is right here this one All right Here is an example of the right hand motor rule. We have a current. Which way is the current going? Now if you're finding this tough I'm gonna stand up and do it on the screen you may find it easier to tilt your paper 90 degrees So it's at the same alignment as the screen. I'm gonna stand up which way is the current going up the page Which way is the external magnetic field extend my fingers that way which way is my phone pointing? What's the correct answer is the answer ABC or DC? Into the page Which way is your Paul? No, no, don't no, no, no, okay, Calvin you did this you and then you turned your hand totally different paper up Right this yes this yes, which way is my phone pointing into the page By the way, some people do this like a gun some people point thumb point finger and then they extend this finger I can't extend my middle finger in the direction of the first of all I'm flipping you the bird I don't want to do that accidentally, but honestly, I can't I can't bend this the right my I got this thing My fingers are kind of double jointed or whatever. So I go boom boom palm You will see some textbooks go boom boom and then Point this finger that way I just can't do it when we say into the page, right? example three Little tougher now Here we have a proton moving a proton moving. That's actually the same as a current It's just not in a wire, but it is a moving charge Which way is this charge moving and this is where it gets tough because Lorely now we have a three-dimensional Diagram on a flat surface. So we really have to use our Sesame Street imagination first thing Which way is the magnetic field see the two magnets? We're gonna have to add the magnetic field lines magnetic field lines always point from what to what do you remember? So can you draw those in there's your magnetic field lines? And let's see which way this proton will get deflected I point my thumb in the direction that the current is going kind of like that My fingers in the direction of the magnetic field is the answer a b c or g Which way is my palm point? I Think towards the bottom of the page. It's really tough with the three-dimensional diagrams I almost prefer a straight-on flat 2d diagram, but I'm sure somebody paid for the graphics and was very very happy Let me see if I got a couple more. I want to do I want to leave you guys some to practice Find number 11. Number 11 got chopped partly in half So find the complete number 11, which is right above the number 12. Okay? Which way is the positive charge the conventional current which way is it moving what your thumb to the right? This time I'm not lifting my hands up at all. You're gonna try and do it yourself Which way is that magnetic field? What is those what are those X's mean? Yeah, now they told you into the page They usually won't it does say into the page so extend your fingers into the page Down at your own piece of paper there thumb down Thumb to the Leslie which way is the current? Point your thumb to the right which way is the met keep your thumb pointing to the right no to the right Look at your piece of that's to the right. You're going like that. I think to the right. You know is that on my okay? Extend your fingers out point them into the page. You have to be flexible a little bit get more flexible Which way is your palm pointing? Which is the correct answer here a b c or d? See Okay Okay Pardon me You asked a good question. It's important ask You've heard me say this Amrit Extend your fingers. No Ben extend your fingers in the direction of the magnetic field. So it's point point palm or point point palm Point point none of this If you're going like this, uh-uh Back to our notes, please example eight example eight This diagram they love to give you this diagram What's moving to the right this time an Electron the right hand rule does not work for electrons. It works for protons Oh and electron moving to the right. What would that be the same as a proton moving to the? So if they give you an electron point your thumb in the opposite direction And it'll often be an electron because those are the charges that are usually moving so I'm going to point my thumb to the left Which way is my magnetic field? What are those X's mean into the page? So if you're using my screen as your frame of reference, I think the force is down the page Or if you were doing it looking at your piece of paper, you would have gone left Into the piece of paper down the page Right, so we've seen that there is a force on Moving charges in a B field by the way, what's a B field? What's a capital B at abbreviation for? magnetic field We know how to find the direction boom boom boom boom boom boom boom boom boom. Okay How do we calculate the magnitude? The magnetic force on a moving charge is equal to three things affected Q V B It's affected by how big the charge is Q How fast it's moving Or house and how strong the magnetic field is But my right hand rule for it to work Everything has to be perpendicular. So I'm gonna add a little Perpendicular perpendicular this formula is on your formula sheet, but they don't put the perpendicular is in there What if they're not perpendicular at QVB at equals the fact I think it's the first one on this on the sheet, right QVB that works out to Newton's believe it or not What coulombs times meters per second times Tesla's works out to yeah, it does We haven't really defined what a Tesla is, but it actually has us. It's It's a unit as well. We talked about a test the last class Sometimes Kelvin the charges don't move at 90 degrees to the magnetic field in which case you find a component and Almost always the component is signed. In fact, you're going to notice if you turn the page That actually next year those of you that go to go to university. You're going to learn the equation as QVB sign theta. Oh Who's in math 12 if theta is 90 degrees if they're perpendicular What's the sign of 90 degrees remember? One and you just get QVB are in other words our original formula actually has an invisible sign of 90 next to it. Oh What if theta is zero degrees? What if they're parallel? What was the sign of zero degrees? Kelvin Are you know you I thought you said it? Oh I thought you heard about I heard you say it. I'm sorry zero What we what Michael Faraday and Ampere and other mathematicians found other physicists found was What deflects charges is when it cuts across magnetic field lines if it goes parallel to magnetic field lines It won't get deflected So we're going to write this if it's parallel No force and they love to do that as a trick question Alex every second or third Provincial and I think somewhere on your test. You'll see me give you an electron trundling along Parallel to a magnetic field and I'll say what's the angle of that? What's the deflection? What's the direction? No, no Faraday showed that actually it needs to cross magnetic field lines for it to get deflected in fact the maximum force is experienced when it's perpendicular This is what they're doing at the large Hadron collider at the large Hadron collider The way they collide particles the way they aim them towards each other They have big big huge huge huge magnets They get the charges going very fast and then they deflect them into each other This is the physics So Example 9 a proton moving at 1.7 times 10 to the 6th meters per second enters a point one five test the magnetic field at Right angles so it is perpendicular. Yeah What's the net force on the proton? So a proton being deflected by a magnetic field the force is QVB What's the charge on a proton? What's the charge on a proton? Victoria One point good old 1.6 times 10 to the negative 19 V is the velocity the velocity here. It says is 1.7 times 10 to the 6th and The magnetic field is pretty big point one five Teslas remember we said 50 Tesla's is huge What force will this proton experience get your calculators out crimson numbers? Sophie what you get times 10 to the 4.08 times 10 to negative 14 is that right? Yeah, okay Nutrients now that seems really small And then negative 14 seems very small But the second part asks what's the acceleration if I know the force on an object. How can I find the acceleration? Oh? Yeah Acceleration is always force divided by mass. So if I take this 4.08 Times 10 to the negative 14 and I divide by the mass of a proton, which I don't know it's 1.67 But I can never remember the times 10 to the Negative 27 how much is this proton being accelerated by and I think the answer is holy smokes really big Kim 2.4 times 10 to the 13th. Is that right? meters per second squared That means if it was able to accelerate for a whole second it would be going faster than light It won't be able to accelerate for a whole second. Otherwise, we'd be violating Relativity, what's the force on a moving charge QBB? QBB and you don't realize yet just how profound that is This is the beginnings of how a generator works Just to show you that you can deflect charges If you take an old TV screen and don't do this yourself because it'll wreck the TV screen But if you take an old-style TV screen and it bring a magnet to it because remember We said those are electrons hitting the screen when we talked about the cathode ray, too If you bring a magnet to a TV screen, it should get deflected. Let's see Don't do this at home. I don't want angry phone calls from your mom or dad that you've wrecked their plasma away. Okay? But it's very noticeable Bring a magnet near a TV screen Okay, it's deflecting the electrons So don't take my word for it. There it is Not good though for the way they've set up the image. I wouldn't want to do this over and over I'm fairly certain you would do permanent damage But if you see an old like $5 TV screen at a garage sale, buy it, try it Very nice MIT can afford direct TVs. Sadly, I cannot Okay, so what do you need to remember right hand rule QBB? What's your homework? from the right hand rules questions hand out Okay, this thing I would like you to try please the following questions number four five seven 11 I think we already did 11 did we okay 12 13 14 If we already did 14 So 12 13 14 16 19 and that's it for now. Those are all right hand rule direction questions