Marc De Benedetti: Okay guys, welcome to Wednesday's lecture. So we're halfway through the week. So yeah, we're almost there. And I think this is week four, I think.
Marc De Benedetti: Yeah, I think, and I was only six weeks in the course. So we're almost done, week four. So meaning after tomorrow.
Marc De Benedetti: There's only two weeks left in the class and then that's our summer so time is certainly flying by pretty quickly.
Marc De Benedetti: Um, the midterm is March I just have to put the two pieces together because there's the crowd. Mark piece and the multiple choice on canvas and they're right now they're separate. So I just have to sort of
Marc De Benedetti: Match up all the grades from individual students and pair them up properly and then get a nice round number out. I know.
Marc De Benedetti: And then that way, that way I can actually look at the average, more, more accurately, and I can make like a nice little histogram graph for you guys and then show you and
Marc De Benedetti: Yeah, that'll be done for tomorrow I'll make sure that for tomorrow. Okay, I'm moving on. So we started induction yesterday.
Marc De Benedetti: Yesterday I recap that in this course. So far, we had looked at the first me first three but three of the four Maxwell's equations.
Marc De Benedetti: There is a sort of unspoken order to them. The first one is gases last second one is guesses offer magnetism.
Marc De Benedetti: The fourth one historically people physicists will call us. The fourth one is an peers law. So those are the three we had done and yesterday we we introduced the fourth Maxwell's equations, which is actually the third one in the list.
Marc De Benedetti: Is Faraday's Law and fairness law described that a changing magnetic flux can actually induce an E field and, you know, we can take advantage of that he field.
Marc De Benedetti: You know you can any field inside of a conductor will make electrons move or make charges move and, you know,
Marc De Benedetti: Even if it's not in the conductor. You know, it will still induce any field. It just means, if it's not in the conductor, they're not able to readily move, although I suppose our definition of conductor was sort of
Marc De Benedetti: Lucy, Lucy. So if you induced enough voltage anything is really considered a conductor. So, you know, there is through that as well.
Marc De Benedetti: So we left off with this worked problem, the previous problem we did was a conceptual one
Marc De Benedetti: Where we were trying to use Faraday's law or and or lenses law to figure out the direction of the induced current. So let's do a very concrete numerical example from here. Let's see here. Let me just
Marc De Benedetti: Throw away.
Marc De Benedetti: Nope, I gotta delete. Okay.
Marc De Benedetti: What fun. There's probably a faster way to have deleted that. But that's okay.
Marc De Benedetti: Okay, so let's let's work on this example here. Just, just to refresh our memory. I guess of what we were talking about yesterday.
Marc De Benedetti: So a 100 loop square coil of wire that hasn't known side length of L equals five centimeters and a total resistance. Okay, that's going to be important. Our total it's going to be 100 homes.
Marc De Benedetti: And it's positioned perpendicular. Okay, awesome. That is perpendicular, because that means you don't have to worry about any angles.
Marc De Benedetti: To a uniform. Okay, awesome. It's uniform. We don't have to worry about a variable, the field and its strength is 0.6 Tesla, I suppose me know the the side length is also five centimeters.
Marc De Benedetti: The, the square loop is then quickly pulled from the field at a constant speed. So it's important to note that it's a constant speed because
Marc De Benedetti: You can balance, whatever, like easily balance you think Ethernet equals ma, you can easily balance.
Marc De Benedetti: The required for us to pull with the opposing force right if that that means the two are equal to each other if there was an acceleration involved and you know the applied for us will be larger and the resistive for us.
Marc De Benedetti: So that's, that's important here at a constant speed constant speed means the acceleration is equal to zero.
Marc De Benedetti: And it pulls out where the field of broccoli drops to zero. So that's a fancy way of just saying no beef eagle.
Marc De Benedetti: It takes a duration.
Marc De Benedetti: Delta t of
Marc De Benedetti: Point one seconds for the coil to reach
Marc De Benedetti: The, the free region. So it takes point in very small amount of time point one seconds to be completely pulled out of the magnetic field.
Marc De Benedetti: The rate. So then you have to count. Using this information with to calculate the rate of change of the flux through one of the many loops. We're sorry real snow and equals 100 loops.
Marc De Benedetti: So what is the rate of change of flux through one of the loops. So A is asking for the rate of change of flux. So that's the derivative of flux with respect to time.
Marc De Benedetti: Through one of the loops. Well, we know what flux is equal to
Marc De Benedetti: Flux is equal to be a
Marc De Benedetti: Cos theta. Now in this class. I mean derivatives are fairly simple derivatives are actually a prerequisite that we expect students to have from grade 12 calculus and vectors MTV for you. Oh.
Marc De Benedetti: The only derivatives were ever going to need in this level of physics is is readily taught in grade 12 so you don't even need first year.
Marc De Benedetti: First year calculus, although if you had it. That would be an even more recent refresher for you. But here, for instance, we don't actually need calculus. Here we can sort of approximate this derivative to actually be the change in flux.
Marc De Benedetti: over the change in time. Now, I'm not saying will never need the derivative in this class, but the derivative. I'm just reminding you, the derivative is a prerequisite skill that we expect that you have from grade 12 calculus and vectors.
Marc De Benedetti: But here, the reason why we're doing this is because
Marc De Benedetti: We don't have a formula for the magnetic field of the function of location we don't you know a doesn't change data doesn't change. So here we're just going to simply compare the flux through the loop before and the fluff through after. So this is going to be
Marc De Benedetti: The flux
Marc De Benedetti: In position to minus the flux in position one over the change in time. So now we go back to be a coach theta, the flux in position to is zero position to is one and is
Marc De Benedetti: Pulled out of the magnetic field. And then the flux and position one is simply be time today.
Marc De Benedetti: And maybe I can put that in brackets there to show you if it's a thing together so
Marc De Benedetti: The total amount of field lines going through the square loop when it didn't. The field is is the time a whatever the strength of the be field is times the the area of that square loop and then you divide this by
Marc De Benedetti: Delta t and then you get simply be a divided by delta t i guess technically you get negative BA delta t.
Marc De Benedetti: So just to make sure we're answering the question properly. It's going to scroll back here, it says
Marc De Benedetti: Part A, find the rate of change of the flux through one of the loop. So there you go, the rate of change of the flux there. One of the loops is is b times a divided by delta t. So that's going to be
Marc De Benedetti: See here 0.6 delta 2.1 so 0.6 I guess there's still a negative sign out front.
Marc De Benedetti: Divided by 0.1 and then A is five centimeters squared. Right. It's a square. So it just length times length. So this is going to be minus six times 0.025
Marc De Benedetti: And that's going to be whatever that happens to be whatever that number is. Although, in fairness, the formula is far more important in this calculation. Then the final number
Marc De Benedetti: So let's say you do parte de
Marc De Benedetti: The total the total induced emf
Marc De Benedetti: In in sort of the total EMF and the current in the entire coil. So for be we want the total induced EMF. Okay, so that means Faraday's law.
Marc De Benedetti: To the induced emf is going to equal to
Marc De Benedetti: Negative n times that changed in flux, with respect to time. So this is Faraday's Law and the total flux would be 100 loops times our answer from part day or answer from Part A is BE A over delta t.
Marc De Benedetti: So our answer our answer really should be 100 times that have part 100 times bigger. That is then part day
Marc De Benedetti: Just to make sure.
Marc De Benedetti: We are sort of on the right track. We see here that the answer for. Let me draw a different color. The answer report a is minus 1.5 70 Weber scenting like centimeter times 10 to the minus to
Marc De Benedetti: This formula says here that we should have something 100 times larger than what we've got in our day. So if you know our answer for Part B, as you can see is 1.5 volts. Well,
Marc De Benedetti: What like 1.5 cents. You ever get rid of the center you get 1.5 so this seems to be be fitting with what with what the answer, say the other thing they wanted to impart be is the total current in the entire coil. So for the total current we use owns long so for total current
Marc De Benedetti: We use owns law for owns lives v equals IR. If you remember from your studying for your midterm and the previous chapters.
Marc De Benedetti: Now our voltage is not coming from a battery and I already said that in this class. I'm going to try very hard to remember to use that script. He when we're dealing with an induced voltage instead of like a a wall or a battery voltage. So in this case, this is going to be
Marc De Benedetti: The induced voltage times i are which means the current is going to be the induced emf
Marc De Benedetti: Divided by the resistance, but we already know what the induced emf is and the entire coil. It's going to be 100 times be a over our delta team.
Marc De Benedetti: So like ours is around there from the current calculation and the delta t is there from the EMF calculation. And again, you can just, you know, plug in
Marc De Benedetti: Plug in your values. Now, I think we, we looked at the answer for Part B. I think the answer for Part B was 1.5 volts and the resistance was 100 100. Oh boy. That's a terrible 100 is 100 homes. So this is going to be 1.5 70 amps.
Marc De Benedetti: Or you know times 10 to the minus two like centimeter comes into the mind to. So that's B and C on into I'm renting a room here.
Marc De Benedetti: There we go. And then see
Marc De Benedetti: Is asking for how much energy is dissipated in the coil well energy. Well, in this case, what type of energy are we talking about are we talking about kinetic energy gravitational potential energy.
Marc De Benedetti: Electrical potential energy, the capacity and the energy in a capacitor. What kind of energy are we talking about here.
Marc De Benedetti: So in the context of of current the energy that's dissipated in an electrical circuit is usually will do to heat in some in some fashion. I mean,
Marc De Benedetti: If you're using your circuit to power a TV, then yes. I mean, part of the energy goes into creating light and sound and stuff like that but
Marc De Benedetti: Generally any piece of electrical equipment that requires power in a circuit diagram you can represent that as a resistor.
Marc De Benedetti: And we usually say, you know, when. How much energy does it consume, we're talking about, you know, it's totally whether the TVs is using some of the energy for sound output some of its for the the the LCD screen.
Marc De Benedetti: The LCD screen itself will throw some heat. We just kind of love, all in together and call that just total energy of being wasted electrically
Marc De Benedetti: And we just calculate, we just say that that's that's electrical heat to our electrical energy that's wasted. Now, it's not a cool loan big energy. So that's what I'm trying to say here is how much energy is wasted on the same note that
Marc De Benedetti: It is not
Marc De Benedetti: Cool alone BIC energy. Right. Hello, big energy is is the potential energy to charged particles have relative to each other.
Marc De Benedetti: And colombe means the word Columbia and physics means to individually terms particles. This is not that. So this is talking about circuit energy and how much energy passes through. So this is where we actually have to borrow our knowledge of power and how it relates to energy. So we say
Marc De Benedetti: When we say power is going to be energy consumed over time. So we reviewed that in a previous chapter, and we're asked for energy. So we can obviously solve for energy. So it's going to be power times delta t.
Marc De Benedetti: And then we ask yourself, Okay, well, what do we have, what do we need. We have delta t. Right, delta t 0.1 seconds. So that's, that's cool. However, we don't know power right so what
Marc De Benedetti: What formulas, do we have for power. Well, you might remember that we have p equals IV as our as our base formula for power.
Marc De Benedetti: And we have voltage total voltage from Part B. And we also have total current from part and be as well. Now, you could use people's IV. Absolutely. And we have the formula for be we have
Marc De Benedetti: A, we have a formula for v. We have a formula for I you can just use those and multiply them together and Bob's your uncle, however.
Marc De Benedetti: I'm just going to warn you that there are no hero marks and physics. Actually, there are no hero marks in life. So
Marc De Benedetti: A wise and more wise approach would be to approach this actually any question in any course. This course or or any course.
Marc De Benedetti: To minimize the chance that you carry forward on the steak. So, yes, you may have made a mistake in calculating the total the total voltage and if you did I, you know,
Marc De Benedetti: There's nothing to help you there. But let's say there is a there's a slightly less risk that you got the first part. Correct. And then you, you messed up in the second part.
Marc De Benedetti: Right, so perhaps what we have is we have voltage. Let's not use to calculated values. Let's see if we can only use one calculated value.
Marc De Benedetti: So let's try to get everything in terms of voltage so we can swap out current in with with owns law and
Marc De Benedetti: And and then get everything in terms of volts. And we were given a resistance with the constant so that doesn't really introduce any any risk of us have a screwing it up.
Marc De Benedetti: So vehicles I are so we can replace i with V over R. So you're going to get v squared over are now again, I can't stress this enough. They're both equivalent
Marc De Benedetti: It's just, they're only equivalent if you assume you've done the current calculation correctly. And you may not have
Marc De Benedetti: Right. Your calculator mistakes. There's plus minus mistakes or substitution mistakes. I'm trying to mitigate the chance of you propagating forward an error that you may have made.
Marc De Benedetti: So it's just a technique. I've learned in my many years of doing well, science, and it's always good practice to do. So let's move forward with that.
Marc De Benedetti: So P is going to be v squared over our times delta t. And we are given delta t were given our thoughts, no problem, v is actually the electric motor force.
Marc De Benedetti: And we calculated that previously. So that's going to be, let's see here and be a
Marc De Benedetti: Over delta t squared.
Marc De Benedetti: Times delta t.
Marc De Benedetti: All over our okay so that's me plugging everything in. And then after I do some simplifying
Marc De Benedetti: Some, some simplifying the delta one of the Delta teams will cancel, and I'm going to get n squared b squared, not delta A squared over see here are delta t. There you go. And that equals the electrical energy.
Marc De Benedetti: That was dissipated in in the circuit or the coil during the time that you pulled it out so
Marc De Benedetti: If, if you were to place, you know,
Marc De Benedetti: Some sort of resistor there, whether that be a light bulb, whether that be a TV or a speaker or
Marc De Benedetti: Literally anything electrical as you're pulling the coil out of the electric field. You could use this much.
Marc De Benedetti: Electrical energy jewels this this many jewels to help power that electrical device. So this is a way in which you can convert mechanical energy into electrical energy.
Marc De Benedetti: Mechanical energy means with your muscles. You're literally using your muscles to move a coil back and forth, or to move a coil in one direction and
Marc De Benedetti: That amount of work done through Faraday's law can be transformed into electrical energy. And then that can be used to power any device, you need. And this is really this is
Marc De Benedetti: The core
Marc De Benedetti: Of
Marc De Benedetti: The premise of generators
Marc De Benedetti: You know how like you know you've got a generator in your car actually called an alternator, you know, some cottages might have like a gas generator outside
Marc De Benedetti: You know hospitals have to have generators on the roof in case the power goes out.
Marc De Benedetti: You know, a generator is a way to, to, to use mechanical energy, you know, you can burn some gasoline to mimic your arm going back and forth, you can burn some gasoline to turn an engine.
Marc De Benedetti: And then you can use that sort of rotational motion to like move a coil continuously in and out, in and out, in and out.
Marc De Benedetti: And then you constantly get these these jewels of energy to put toward powering electrical devices. So that's where eventually we will be going with this chapter, we will be talking about generators, but in due time.
Marc De Benedetti: Okay, next up
Marc De Benedetti: So we can talk about induced voltage and and moving conductor.
Marc De Benedetti: Up until now, we have been looking at a loop of a closed circuit like a conducting circle or conducting square
Marc De Benedetti: And how you can manipulate the flux and there's three ways to manipulate flux right there's be you can change the field. You can change the area of the loop or you can change the angle of the the field, right, all of which will change the flux across a certain area.
Marc De Benedetti: However, it just so happens that you don't necessarily need
Marc De Benedetti: A loop or an enclosed area of liar or conductor to generate a V field. All you need is a moving conductor. So even a rod that's moving
Marc De Benedetti: You can induce a voltage in that Ron. So consider this for a second. Consider this is called a rail gun. By the way, I'll have a video for the rail gun.
Marc De Benedetti: Later on the slides. But consider this. You have a conducting wire that you bolt to the table, you know, maybe you glue it or you tack it down with some
Marc De Benedetti: Nails or something like that. I don't know if it's part of the ground to conducting wire that's part of the ground. And what you do is you have a metal rod.
Marc De Benedetti: That you just loosely place on top. You don't, you know, like glue it down or nail it down. It's just placed on top of the metal the metal rails.
Marc De Benedetti: And then what you do is you grab the rail with your hand and you physically with your muscles you physically pull it this way with with some sort of force.
Marc De Benedetti: Now if you pull it this way, obviously it will have some sort of speed Z inherently. Now, why is this being talked about why is this even a thing I'm bringing up on the lecture slide.
Marc De Benedetti: Well, the point of the conducting the red conducting rails that I've drawn is that there is a loop that is formed between
Marc De Benedetti: This loose metal rod and the Wii U shaped rails that are attached to the ground. Right. Everything is a is a conductor. So as long as they're touching, then they're they're forming an electrical loop.
Marc De Benedetti: Now, here is another way that you can you can manipulate fairies law to your advantage. What's happening here is when you first put the metal rail down the metal rod down, it forms, some sort of enclosed area.
Marc De Benedetti: Let me maybe write that in a different color. It forms, some sort of enclosed area.
Marc De Benedetti: And when you pull the rod. In this example, you're pulling the Ron to the right. When you pull the rod, what you're doing is you're increasing the area.
Marc De Benedetti: So that's a change in flux, you're changing the number of field lines that are going through the area. I'm going to erase my doodles for a second. So you can see better
Marc De Benedetti: So originally we have 123456 field lines going through that area, but as I pull it forward, maybe half a second later, I've now encompassed
Marc De Benedetti: Two more field lines. Then I then I used to just a moment ago. So that's a change in the flux. That's a change in the number of field lines. But what variable and I'm manipulating my my manipulating the angle.
Marc De Benedetti: Know that the field is still into the page. The, the orange out of the page. The areas. A lot of the page for the angle is confident
Marc De Benedetti: The strength of the BC, although my manipulating the strength of the field. Know what I am manipulating is the area. The total area. So if you look at Faraday's law.
Marc De Benedetti: Right there, it says the induced voltage EMF is going to be equal to the changing flux well flux is the derivative of be times A with respect to time. Now, we think to ourselves,
Marc De Benedetti: When you have a derivative
Marc De Benedetti: You are able to factor Constance out of the derivative. So we say, Okay, which one is changing. Maybe they're both changing if they're both changing that. Oh boy them to do product for all. That's really annoying.
Marc De Benedetti: However, if they're, they're not both changing. Luckily, the field is constant. So we can actually factor of the the field and we can say this is just going to be times the derivative very
Marc De Benedetti: All right, well, what kind of area. Do we have, is it a circle that's just getting bigger. Is it a circle that's getting smaller is the circle that's keeping the same perimeter, but just being deformed what's happening.
Marc De Benedetti: Well, what's happening here is we have a rectangle that is maintaining the same width, but is getting longer, or, I guess, maintaining the same height, I should say.
Marc De Benedetti: But getting longer with time. So I guess they've they've labeled the, the, the height L for life. I suppose so, I'll use their notation. So I make notes here that the area is actually equal to length times width.
Marc De Benedetti: And then again, when a rectangle changes. There's no guarantee that only one dimension, changing at a time. If you have the length and the width both changing simultaneously, then you'd have to use product rule.
Marc De Benedetti: However, in a rail gun. The rails are constants. All you're doing is you're making the width longer so we again can factor out
Marc De Benedetti: The L.
Marc De Benedetti: And we get that the induced voltage is b times length times the derivative of the width. The rate at which the width is increasing. Now this is a function of how fast you're pulling the faster you pull the faster the width is increasing.
Marc De Benedetti: The, the slower you pull. Obviously, the slower with is increasing so we can represent this in fact by a function of time. So we can say that
Marc De Benedetti: This is going to be be L and width or the derivative of with, I should say, it can be represented by speed times dt. And then we have that sort of Dt there. And just to be clear, as as what substitution. I DID. I SAID THE DERIVATIVE OF width is going to be speed times the derivative of time.
Marc De Benedetti: And if you don't know where that came from. That's velocity equals distance over time.
Marc De Benedetti: Or more specifically the change in distance over the change in time.
Marc De Benedetti: So here in this equation, the delta to cancel or the DTS cancel and then you end up getting be l v equals induced EMF. Now, interestingly,
Marc De Benedetti: That was a fairly easy derivation muy Thai say, however, the interesting part of the result is that area of the loop is not within itself.
Marc De Benedetti: In the answer right. We use the area to to to make the derivation, but the answer itself does not depend on the area, which makes sense, right, because
Marc De Benedetti: The induced emf is not a function of the flux. It's a function of the change in flux and the change in flux in this instance is not a function of how big the area already is. It's a matter of how fast the area is increasing. So an interesting implication of this formula.
Marc De Benedetti: Is because there's no area. I'll say. Note that there is no area in the answer, it led physicists to sort of think, well, hold on.
Marc De Benedetti: Maybe we don't even need a closed loop. Maybe we don't even need an area because the answer isn't the theme juice voltage isn't the function of
Marc De Benedetti: The function of the length of the rod and the speed of the rod. So interestingly, they went to go test that and they just took a simple metal rod.
Marc De Benedetti: And they moved it through a magnetic field by pulling it
Marc De Benedetti: And they were with without a complete circuit. It was just a rod and they were able to confirm that there was a potential difference between the ends of the rod.
Marc De Benedetti: Now the difference being there's no current. So, I will say,
Marc De Benedetti: In we can get
Marc De Benedetti: And induced
Marc De Benedetti: Voltage
Marc De Benedetti: In a moving
Marc De Benedetti: Rod
Marc De Benedetti: However,
Marc De Benedetti: Since there is no complete
Marc De Benedetti: Circuit.
Marc De Benedetti: There is no current
Marc De Benedetti: Just because there's no current doesn't mean there's no voltage. Okay, so this comes back to be like insulator and conductor argument.
Marc De Benedetti: You know, you can think of air as as a conductor at a very, very high voltage. But if you're not at that breakdown voltage, you're not going to complete the circuit. So really, all that's happening here is you are creating a separation of charge.
Marc De Benedetti: So in blue here. I'm going to say you are creating
Marc De Benedetti: A separation of charge.
Marc De Benedetti: Which can be thought of as sort of a dipole if you'd like.
Marc De Benedetti: Another way you can think of it is. It's sort of analogous
Marc De Benedetti: Sort of like
Marc De Benedetti: Capacity capacitor capacitor has positive charges on one plate and then nothing and then negative charges on the other plate and that's effectively what is happening here.
Marc De Benedetti: Now, if you're trying to wrap your head around. Well, Mark. There's no complete circuit. There's no area, how to even calculate flux when there's no area. How does this work.
Marc De Benedetti: Another way to explain this phenomenon, although you you can't get the formula. This way. But another way to conceptually represent this phenomenon.
Marc De Benedetti: Is we know the magnetic force on a moving charged particle, not on a circuit, not on a current just
Marc De Benedetti: An individual charged particle. We talked about this way back and Magneto statics, I think it was beginning last week, you know, for instance, take an electron, a loose loose electron in this conductor.
Marc De Benedetti: And it's an electron. So you use your left hand, not your right and your left hand.
Marc De Benedetti: And you can use a few right hand rules. If you want, you can use the physics gangster sign, just with your left hand, instead of your right hand. So your thumb is to thrust your index fingers, the current concert with I
Marc De Benedetti: Or the velocity and then your middle fingers and magnetic field. So if you prefer to use the physics gangster sign you can go nuts.
Marc De Benedetti: If you prefer to, you know, the US, the give me money right hand rule, I guess, in the sense split just left hand.
Marc De Benedetti: You can use that one to I'm going to use to give me money one so fingernails in the direction that the field. So, left hand fingernails over the page because that's what we see here is little dots.
Marc De Benedetti: My thumb has the point in the direction of the velocity of to flip my hand upside down my thumb is pointing to the right, my fingernails are pointing at me and the palm of my hand is facing upwards.
Marc De Benedetti: So you see here that using Magneto static principles, not even Faraday's law but Magneto static principles, you can actually predict that the negative charges or the electrons in this rod will actually feel an electric forced upwards.
Marc De Benedetti: And they will move, they will literally separate. So, um, I shouldn't say there isn't any current I should say that there is a small amount of currency for a very short period of time.
Marc De Benedetti: While the charges are in the middle of separating. However, once they're separated and all the negatives no negatives are blue.
Marc De Benedetti: While all the negatives. Once all the negative hit one end, they have nowhere to go. So they pile up there and then they just stay there stationary. So when I say there's no current I mean after things have been separated. There's no current
Marc De Benedetti: If you had a complete circuit, they would just keep flowing around in a circle because that's what a circuit is but when there isn't a complete circuit, they don't they just go to one end and stay there. Just like a parallel play capacitor or like when you induce a dipole
Marc De Benedetti: And obviously the other end is read it because it's positive, and all the textbooks use read
Marc De Benedetti: And if you want to know where the positive go even though we know now in modern science, the positives don't actually move on. You can use your right hand rule.
Marc De Benedetti: You know fingernails over the board. Your right hand, a son is pointing to the right, your palm is pointing down. So that's another way to to analyze this
Marc De Benedetti: So this means that a moving rod will actually have a potential difference between the two ends of the run a little side story.
Marc De Benedetti: Can you think in real life. Can you think of a real life example of a metal rod or what could be approximated, I suppose, as a as a metal rod that is moving through a magnetic field on a regular basis.
Marc De Benedetti: Actually, I'm gonna open the chat. Now, if I want to see.
Marc De Benedetti: Who I hit something. What did I did.
Marc De Benedetti: I okay let me. I don't know what I clicked. I'm going to go back to the chat.
Marc De Benedetti: And now the chat isn't opening. Of course it's not.
Marc De Benedetti: Okay, hold on. Welcome to Microsoft products. There we go. Okay.
Marc De Benedetti: Um,
Marc De Benedetti: Okay, so here's the question. It can you think of a real life example of when a metal rod.
Marc De Benedetti: Is traveling through a magnetic field is that is that, can you think of a real life example of when this would happen on a fairly regular basis. And I know we all, we all know what this is what I'm trying to get it on. We all know what this is.
Marc De Benedetti: And to answer your question, Rodrigo yes you can deduce the sign.
Marc De Benedetti: Of the side based on the field well and and the direction of motion, right, because it's a cross product.
Marc De Benedetti: Q v Crosby. If you remember the right hand rule, the formula for that is f equals Q v Crosby, so you need to know both the direction to be field and the direction function.
Marc De Benedetti: Okay. Does anyone have any ideas of in real life. When you would when when you would get an actual metal rod or something that can be approximated as a metal rod movies through a magnetic field. Any ideas.
Marc De Benedetti: Hmm, okay. I'm not seeing anything coming through. So I know everyone, and especially in today's climate. There's a lot of talk about about this specific thing here.
Marc De Benedetti: And electric guitar bridge. That's an interesting thought. Although, although electric guitar bridges do use
Marc De Benedetti: They do use the principle of Faraday's Law. It's a little bit different. And we will talk about electric well the premise of electric guitars later on. It's actually transformers. It's not solely just this. What I'm getting at here is actually airplanes.
Marc De Benedetti: And now with coven the topic of air travel is is a big, the big thing right now. Do you really want to get on you know in a in a Petri dish of an airplane.
Marc De Benedetti: And travel with with recycled air for any length of time during coven but anyway. Point being an airplane. The wings. Even the fuselage, but the wings are, you know, a metal conductor from tip to tip.
Marc De Benedetti: And the Earth has its own magnetic field, right. We know the North Pole is well geographic north of North, which is weird. We
Marc De Benedetti: Will not so we're the ones you know but magnetic sales. So the Earth has its own magnetic field and when airplanes are traveling, they're traveling through a constant magnetic field. So the you can actually approximate this. Come on, you can actually approximate this as
Marc De Benedetti: An airplane flying
Marc De Benedetti: And there's actually circuitry in the plane that has to accommodate for the put the voltage difference between the wind tips because you know that could cause you know interference with other instruments.
Marc De Benedetti: There's a, it's a buildup of charge. And you know, when you have motorized mechanical things in a device. They are definitely sensitive to the flow of charge because the flow of charge of the current so
Marc De Benedetti: You know there has to be accommodations for that the engineers on an airplane have to sort of take this into consideration.
Marc De Benedetti: And it's not big. It's not going to cause any sparks or lightning or anything, but it's enough that
Marc De Benedetti: It could maybe cause some safety issues when you're flying the plane and you want you want a certain aspect of the plane to do something you need to depend that it reacts to what what you're telling it to do and you you can't afford to have any sort of
Marc De Benedetti: Mechanical malfunctions of any sort, let alone due to some physics phenomenon that is well established right so that's just unacceptable.
Marc De Benedetti: So anyway, I just thought, That's a cool example of
Marc De Benedetti: That
Marc De Benedetti: OK, so moving on. We. We. Let's go back to the rail gun for a second. If we look back at the real going and if we if we kind of put this this rod.
Marc De Benedetti: Rod back onto a U shaped rail, we can use lenses law to figure out the direction of the induced current. So if, if we are pulling the rod to the right.
Marc De Benedetti: We are increasing the number of field lines through the surface.
Marc De Benedetti: Okay so lenses law says a current will be induced to oppose that. So we are increasing the number of field lines out of the page. So we want to decrease the number of field lines out of the page. So the, the
Marc De Benedetti: Lenses law says the induced magnetic field won't be out of the page, it will be into the page. So use your right hand, put your thumb into the screen and then wrap your fingernails.
Marc De Benedetti: And that the direction of your fingernails will show you the direction of the induced current as a result of fairies law or lenses law.
Marc De Benedetti: So here you see the induced current will be
Marc De Benedetti: Clockwise. And there are many ways to think about this. Again, if you want to think about the
Marc De Benedetti: Individual charges is all current is is just a series of charges that are lined up in a neat row like you were in kindergarten.
Marc De Benedetti: So you know if you want you can think of. You can think of a positive charge.
Marc De Benedetti: In in this in this rod here a single lonely positive charge in this wire and you can use F equals if you wanted to, you could use F equals Q, the cross be
Marc De Benedetti: And you can use your physics gangster sign you can use to give me money. And you can see that the positive charges would be forced downward and that also tells you that if if that was hooked up to the rest of a circuit, then it would be flowing clockwise
Marc De Benedetti: Okay.
Marc De Benedetti: So I think, I think that's mostly what we oh sorry here, there's an aspect that we haven't talked about yet. So there's no such thing as a free lunch.
Marc De Benedetti: Obviously, that's, that's just a saying that is just universally true whether fee in school or physics or life. There's no such thing as a free lunch. What does that mean in terms of physics. Will it means you can't get something for nothing.
Marc De Benedetti: Before we were pulling on it. There was no current
Marc De Benedetti: Now that we're pulling on it. There's a current. Well, there has to be something Newton's third law, there's a force, causing the current there has to be an equal and opposite reaction for us.
Marc De Benedetti: Right now, we can we can sit here for four years, you know, we can be enforced your physics and we can still talk about the details of
Marc De Benedetti: The mechanism by the force of the forest in the wire that pushes the electrons, yada, yada, yada.
Marc De Benedetti: You can just understand, though, that there's a current or something, forcing them into the field level, blah, blah, blah. But Newton's third law, there's an equal and opposite reaction force. Let's look at that. Now, we know the induced current is downwards.
Marc De Benedetti: Right, we said that on the previous slide.
Marc De Benedetti: Well, look at this equation f equals I ll be
Marc De Benedetti: Okay, it's a very similar equation to f equals Q Vb.
Marc De Benedetti: In fact, it is the same equation is moving the t the division by T to Q instead of the D.
Marc De Benedetti: So f equals I'll be if you have current you can use your fixed gangster sign if you use your current index finger current pointing down.
Marc De Benedetti: Middle finger MS magnetic field is pointing out of the board, then your thumb for thrust is going to be pointing to the right. Sorry to the left.
Marc De Benedetti: To the beyond saying to the left.
Marc De Benedetti: So as you are pulling your arm, your muscles are physically pulling this to the right.
Marc De Benedetti: If you are doing this what your muscles would feel is a resistive force.
Marc De Benedetti: And your brain. Know your eyes can see it, but your brain can't see it. Your brain just feels is a resistive force, it doesn't know where it's coming from.
Marc De Benedetti: And if your eyes didn't go physics, your eyes would be like oh my god this is this is an invisible resistive force its magic. However, the physics says the resistance force is then opposing magnetic force. There's no such thing as a free lunch.
Marc De Benedetti: So this resistive for us is actually so famous because it's unavoidable. In fact, pretty much all the physic can be pretty much summed up by there's no such thing as a free lunch, ie conservation of energy.
Marc De Benedetti: This is so unavoidable and such such an important concept in in circuits and electromagnetism that we've called it a name. It's called eddy currents, named after the person who sort of formalize the notion
Marc De Benedetti: More technically there is called a back EMF
Marc De Benedetti: back EMF resists the flow of the of the current and that's that's what's happening here backing MS is something pulling backwards. If you're pulling it to the right.
Marc De Benedetti: Back enough literally will pull it backwards. It will try to tug of war and we'll try to put it back to the left.
Marc De Benedetti: So it's called it back EMF, technically, but most physicists will will refer to them as something called an eddy current and an eddy current is just a current that is induced that that resists the, the change, it will pull backwards.
Marc De Benedetti: So I want to show you a video of a rail gun because I don't think my explanation is done justice.
Marc De Benedetti: Usually when I teach this class in person. I will bring in a rail gun and I will show you a real gun in person. However, we don't have that luxury this year. So here's the video. I hope you like it. Have a real gun.
Marc De Benedetti: Okay. So you saw there. They had two pieces of electrical tape which is usually used by like furnace people H back people because they use it to wrap ducting
Marc De Benedetti: But physicists love electrical tape and this isn't. It's not really electrical tape is it's not about black Reverend tape.
Marc De Benedetti: It's conducting tape and we use it all the time for fun things like this. So what they're doing here is there they're using that conductive tape.
Marc De Benedetti: On this like a wooden board and that access the sort of metal rails and they have to circular magnets that are connected by probably at aluminum rod or
Marc De Benedetti: Not aluminum probably some sort of steel rod or something. And those those circular magnets are was generating the, the magnetic field in their region because that's, that's a very crucial part of a real gun.
Marc De Benedetti: And because of that magnetic field, you saw them hooking up a battery and you saw them clamping the two ends of the battery to the ends of the of the conductor tape.
Marc De Benedetti: And they sent a current through it and and that's the physics of a real gun. So you saw it, they gave it a little bit of a nudge, and once it was moving. There you go. It was it was a it was a real gun preschool.
Marc De Benedetti: I looked at briefly at the chat while while the video was happening. So to answer the most recent question on the eddy current is the current induced by Faraday's law.
Marc De Benedetti: And when we say like a back EMF, that's just another word for for it. I mean, any of that is a voltage and current, the current
Marc De Benedetti: So, you know, we talked about eddy currents. We're literally talking about the current that is induced as a result of fairness law.
Marc De Benedetti: And then you talk about Bacchae MS is just divide by resist or
Marc De Benedetti: Multiply by resistance you get EMF field equals IR. So once once the current talking about ones ones, the voltage, we're talking about, but they're they're almost interchangeable. As long as you understand that the result is is the the induced induced
Marc De Benedetti: Either current or voltage
Marc De Benedetti: Okay, so here's a conceptual question about real gun. So I want to see kind of how how with me everyone is so I'm going to launch a poll. I couldn't before launch the poll. They don't want to intrude on your screen yet.
Marc De Benedetti: And let me shrink this a little bit so you can see it. So let me launch the poll
Marc De Benedetti: Here we go. So let's see how many of you are following along with me a conducting rods slides on a conducting track at a constant be field that is known to be directed into the page, what is the direction of the induced current
Marc De Benedetti: Clockwise or counterclockwise or no induced current
Marc De Benedetti: Jeopardy music I keep forgetting about the Jeopardy. Music
Marc De Benedetti: Think I saw an interview with Alex Trebek recently.
Marc De Benedetti: I think he wrote a book during, during his coven quarantine.
Marc De Benedetti: interesting guy. I think he spent like almost 30 years or something like that, as the as the host jeopardy.
Marc De Benedetti: A long time
Marc De Benedetti: 62% of you voted.
Marc De Benedetti: 65%
Marc De Benedetti: Or 81 okay that jumps pretty quick.
Marc De Benedetti: Interesting. The results are very interesting
Marc De Benedetti: Okay.
Marc De Benedetti: 84% of you. Okay, I'm going to hide the pole or stop the poll and then I'm going to share the results 37% of you voted a 48% of you voted be and 15% of you voted. See, so it looks like there's a pretty neck and neck race between A and B. So instead of scrolling down and explaining it.
Marc De Benedetti: I'll say a few things, but I won't explain it fully. And then I'm going to relaunch the pole, because I kind of want to see how things are different.
Marc De Benedetti: So we have magnetic field into the page. We have a permanent fixed rail. That is not moving. And then we have a rod a blue rod laying on top that is known to be moving to the right.
Marc De Benedetti: We have that sort of enclosed area. And as it's moving to the right. The that enclosed area is getting larger and the US, including a different amount of magnetic field lines. So it's flux is changing and we are using
Marc De Benedetti: Therapies law and lenses law to predict the direction of the induced current and the induced current lenses law says it's going to be opposing the direction of the change in flux. So, think of it that, again, I'm going to relaunch the poll
Marc De Benedetti: And give it another thought. And I want to see kind of how how that has changed your, your perspective on what's going on here.
Marc De Benedetti: 46% of you.
Marc De Benedetti: 53% of you 59% of you.
Marc De Benedetti: 68% to view 71 we're getting there. I think we hit like 81 or 85% to like that last time percent that is 78%
Marc De Benedetti: Oh yeah, the results are much different now.
Marc De Benedetti: 78 what we got to add something last time, but for the interest of time.
Marc De Benedetti: I'm going to end the poll. If you didn't get a chance to vote. That's okay. You know, again, I'm not marking these about their anonymous. I've got no idea who's, who's voting here. So if you didn't get a chance of totally okay.
Marc De Benedetti: I'm going to end the poll. And now I'm going to share the results again. So it's an overwhelming majority now is be nobody voted seen this time.
Marc De Benedetti: So let's have a look. See, now I'll explain it. I let me stop sharing so you can get your screen back. So let's have a look, see here, what's going on well as the blue rod is moving to the right. We are including more field lines into the page.
Marc De Benedetti: So the change here is more field lines into the page. We want to oppose that. So to oppose more field lines in the induced the field has to be more field lines out
Marc De Benedetti: Out of the page. So the induced the field is out of the page, use your right hand thumb in the direction of out. So, you know, hold it away from the tablet screen presumably pointing at you.
Marc De Benedetti: And then you wrap your fingernails in the direction of where the news current would be so if my thumb is pointing out of the board my fingernails on my right hand would look counter clockwise. So the answer is counter clockwise
Marc De Benedetti: So there you go that fast or counterclockwise
Marc De Benedetti: Okay, I want to delve a little bit deeper into what Eddie current is
Marc De Benedetti: Full disclosure. This slide will not be testable, because we are not going to be studying the math of this type of current
Marc De Benedetti: Previously, when we have a circuit and there was only there was a very well defined path for the current, no problem. We can use owns law farewell Faraday's law first to paint voltage and in conjunction with owns lot to analyze the circuit.
Marc De Benedetti: This slide just shows you how interesting physics can get
Marc De Benedetti: This slide says you don't even need a liar, like a circuit or or or something predefined like a road. Okay, this says, you could have a slab of metal.
Marc De Benedetti: A slab of metal, meaning it's not a wire the electrons are free to move anywhere they desire in the in the two dimensional plane. They can go forward, back up, down in any combination thereof case a slab of metal.
Marc De Benedetti: And what's happening here is you still get eddy currents. Now if you direct a localized magnetic field in a very narrow range of the metal desk.
Marc De Benedetti: This localized magnetic field could be maybe from a hanging bar magnet. Just above you could literally hold a bar magnet, a few inches above this metal disk. That would be one way you could obtain a be field in a local live region of the desk.
Marc De Benedetti: And that alone doesn't cause a current. However, if you rotate the disk, then what's happening is the let's use the positive charges, then the
Marc De Benedetti: What is it, what is physicists thought to be thought to be right now. Wrong. If we look at the positive charges, even though that I know that the electrons that move, but for the sake of
Marc De Benedetti: consistency with the textbook. If we look at the positive charges in the middle here, then what we're doing is we can look at F equals Q Vb.
Marc De Benedetti: Or technically the Crosby. So if you took a positive charge and you were rotating the disc. You were literally rotating or moving that positive charge to the right and the be field is into the page. So if you use your right hand rule be field into the page.
Marc De Benedetti: Velocity or or current to the right, then your thumb or got the palm of your hand point up. So this will actually feel a force.
Marc De Benedetti: Upwards which means it will move upwards. Now, of course, protons. Don't move. We know that now, but anyway.
Marc De Benedetti: So you see here the current the induced current or what we call the any current on the right hand side of this magnetic field as it rotates. You can see the arrows here are pointing
Marc De Benedetti: In a clockwise fashion because here they're feeling forced upwards, which causes clockwise. Now the reason why they don't need a predefined circuit is because we know that
Marc De Benedetti: They mostly will travel in some sort of circular orbit, because we know the the trajectory of a moving particle and the magnetic field. We know that that's going to be circular
Marc De Benedetti: Now this isn't a uniform be field. So it's not perfectly circular, it's going to be some sort of oblong maybe ellipse, maybe something else, but it will still form a loop a closed circuit loop.
Marc De Benedetti: And you will get little circles, you get little squirrels of current and on the other side, let's say you had a proton.
Marc De Benedetti: You had a proton that is coming in on the other side. And it's not experiencing any field and now it is experiencing in the field and it's going to feel the reverse. So it's going to feel something down. No, it's not.
Marc De Benedetti: No, it's not. It's a, it's still here. It's not feeling any force as it moves in as it moves in. It's the same physics. It's the same
Marc De Benedetti: Q equals V Crosby. So as it moves into the region, it's going to feel a current a force upwards, just like the other one.
Marc De Benedetti: But however when it feels the force upwards. It's going to complete it to loop backwards, where this is going to complete it forwards.
Marc De Benedetti: So this is going to be counter clockwise. This is going to be clockwise. You going to get two separate eddy currents and each of these eddy currents. Again, if you use your, your right hand rule, F equals i induced LB picture or current
Marc De Benedetti: Let me erase this for a second picture a short length of wire here with current traveling up
Marc De Benedetti: RIGHT HANDS rule current traveling up fingernails into the board the palm of your hand is facing to the left. So that's going to be a resistive force and they will be. It's actually felt, it's a resistive force that you can feel
Marc De Benedetti: That's really cool. Now I actually there's a there's a very brief video with this and you can see the video.
Marc De Benedetti: Very brief. It happens very, very briefly, you can see it in the theme song or the beginning little intro bit to every single one of our lab videos.
Marc De Benedetti: And I'm going to take a brief cuz I'm doing a lot of talking here, we're doing a lot of review. So I'm gonna take a brief pause and I want to show you now let's see if I can manage this.
Marc De Benedetti: Let's see if I can manage this. I might need my keyboard for this will see here
Marc De Benedetti: Okay, let's see here. Can I find
Marc De Benedetti: Go here. Can I find the
Marc De Benedetti: You TM physics page and the on screen keyboard does not want to work. Okay, let me grab the keyboard.
Marc De Benedetti: Okay, I'm hoping that didn't disrupt to the screen sharing by putting on the keyboard. So let me find you TM physics.
Marc De Benedetti: Here it is.
Marc De Benedetti: So if we find the theme song.
Marc De Benedetti: Oh, I guess it's the theme song, I guess that's, um, that's not necessarily at the beginning of every lab video, have you search your search.
Marc De Benedetti: Theme Song hat. Here it is. So if you look at the theme song for our physics page.
Marc De Benedetti: Come on.
Marc De Benedetti: What's going on.
Marc De Benedetti: Did it freeze on me.
Marc De Benedetti: Oh yeah, the computer froze.
Marc De Benedetti: Okay, the computer froze. I'm asking you to do too many things at once.
Marc De Benedetti: Well, now I can't do anything. Alright hopefully it's still recording. Okay.
Marc De Benedetti: All right, well I can minimize
Marc De Benedetti: All right. Maybe I'll show you later, it will not, it will not work.
Marc De Benedetti: Oh, and I can't what's going on now.
Marc De Benedetti: There we go. Okay, now it's working.
Marc De Benedetti: Okay, that was it right there. In fact, that's my arm in that shot. So you see that we find an aluminum desk that's spinning beneath
Marc De Benedetti: Beneath the magnet and we are hanging a bar or not even a bar. It's like a really, really small bar magnet. We're having a mega off of
Marc De Benedetti: Off of the string that's only a few centimeters above and as the disk below it spins. You see that there is demonstrably a force acting, both on the disk, get on the magnet.
Marc De Benedetti: Because Newton's third law. You can't just have a one sided force if there's a resistive force in the disk that force has to be coming from something and it's coming from
Marc De Benedetti: The magnet. So that Megan also feels a force, but because there's nothing. There's no, like, I'm not holding the magnet in place.
Marc De Benedetti: It's, it's free to pet. It's free to swing on on the string, not like a pendulum. You see the magnet itself is display. So let me just rewind a little bit here and you can watch it one more time.
Marc De Benedetti: So there you go. That's the closest I can, I can get
Marc De Benedetti: Showing I'm demonstration, so to speak, of what an eddy current is again if I was in person. I would absolutely do this for you in person, but this is as close as we can possibly get.
Marc De Benedetti: Okay, so for the interest of time, I don't think I want to pull you here, but I will, I will definitely talk about this. So, in any current example.
Marc De Benedetti: Let's say we had a magnet like a bar magnet and you just drop it in air, you just drop it off the table or or what have you, then you will obviously fall with an acceleration of G.
Marc De Benedetti: Obviously, it's just, that's just an object at that point. However, if you did the exact same magnet and you had a conducting loop and you dropped it through the conducting loop.
Marc De Benedetti: Then we know from Faraday's law that because the magnet is getting closer and closer to to the loop you are changing the flux changing a flux will New Zealand do so voltage and because it's a
Marc De Benedetti: conducting loop the voltage will then induce a current and we know because of lenses law, the induced current will oppose the change, you're going to get an eddy current
Marc De Benedetti: And that will resist the motion. So it'll be it'll be upwards force. So as the magnet fall through here, this copper wire will feel
Marc De Benedetti: Let me change my color here will feel a current what looks to be in and around counterclockwise and this the field that it induces will be a big field upwards.
Marc De Benedetti: To combat the increased be field downwards and the induced the field upwards, the north pole here will repel the north pole with a magnet.
Marc De Benedetti: The slowing down to the acceleration of this magnet will be less than that of G, it will be zero, maybe zero depending if it's if it's if it's alarming of thing but it'll be less than G.
Marc De Benedetti: So it will fall slower. Now, interestingly enough, if you take this copper loop and you turn this copper loop into a copper pipe so you turn the copper loop into a copper pipe.
Marc De Benedetti: Or or equivalent like a solenoid or recoil so many, many, many loops. You can think of this as sort of many, many, many loops copper loops on staff, the top of each other and you repeat this you drop a bar magnet through then
Marc De Benedetti: As it drops it doesn't just have one region in space that that is creating an upwards force as it's dropping every point along its descent.
Marc De Benedetti: Is able to induce a backwards or induce occurrence that opposes this motion. So if you actually have a long enough pipe. If you drop a magnet through
Marc De Benedetti: The magnet will eventually hit terminal velocity because the resistive force, as you know, as a function of speed. Right. You know, Q or F equals Q Vb, the faster you travel, the more the force. So gravity will pull it down.
Marc De Benedetti: And it will accelerate as it accelerates the speed becomes faster and as the speed becomes faster. The, the any current the backwards force will get stronger and
Marc De Benedetti: Eventually it'll equal though, so eventually it'll find the speed at which the upwards force balances gravity and this is the speed. I'll say when when the resistive read this stiff force.
Marc De Benedetti: Balances
Marc De Benedetti: Gravity.
Marc De Benedetti: Then you reach terminal.
Marc De Benedetti: Velocity.
Marc De Benedetti: Okay, so that's that's why
Marc De Benedetti: A falling magnet will will reach terminal velocity in a conductor or some sort of conducting loop, vice versa is also true if you if you were somehow able to drop
Marc De Benedetti: piece of metal through a circular magnet. The same thing would happen. It doesn't matter which ones magnetized its relative motion, whether the magnets moving relative to the wire or the wires moving relative to the magnet.
Marc De Benedetti: is all relative. It doesn't really matter as long as there's movement.
Marc De Benedetti: Okay, so there's actually
Marc De Benedetti: Well, when I think to be very cool example I have a feeling this this example was not done in Canada because in Canada, you have to book an MRI machine like
Marc De Benedetti: Six months in advance and i cant im and they're hugely expensive to operate and to maintain and to purchase. So I can't imagine that anyone that has access to an MRI machine would ever be allowed to waste time on something like this. So something tells me
Marc De Benedetti: This video comes from America. The land of capitalist society where money buys do everything.
Marc De Benedetti: It's a cool video. Nonetheless, I just, I don't think it's Canadian
Marc De Benedetti: What this video I'm about to show you is it is a let me grab a different color here. It is an aluminum slab. Now, why is it important that this is an aluminum slab and not steel well
Marc De Benedetti: In an MRI machine, as many of you who are in pre med know it's a very, very powerful magnet. Well, it's actually an electromagnet. But nonetheless,
Marc De Benedetti: I'm very powerful like using physics. I'll tell you, it's about somewhere between seven and 12 Tesla, depending on how big the MRI machine is and stuff like that.
Marc De Benedetti: That's an incredibly strong and before they put you in there, they make sure that you have no earrings on them jewelry. If your fillings in your in certain types of feelings.
Marc De Benedetti: Will will get ripped out of your, of your, your skull. So, and for people who have the sort of the older style fillings. They're not even able to memorize at all maybe other leg and I keep your face for the way even then it's kind of iffy. So
Marc De Benedetti: You can't use a steel block in this demo because it's still block would just get
Marc De Benedetti: You know, we would just destroy the MRI machine aluminum, however, aluminum is not magnetic if you take a fridge magnet and you try to stick to some aluminum, it won't work.
Marc De Benedetti: I actually just found out my fridge, which I thought was a stainless steel fridge is not, it must be made of aluminum magnets don't stick to it.
Marc De Benedetti: So that was the stick to the side of the fridge, though, but not not the front of the fringe anyway. So here is still metal aluminum still conductor and
Marc De Benedetti: What this demonstration is going to show you is he's going to take a block of aluminum and he's going to nudge it so it's going to fall.
Marc De Benedetti: And if this was done with the, with, with no magnetic field, then it's no different than dropping, dropping an object just it follow that g
Marc De Benedetti: However, if it falls in a magnetic field, then there's going to be a resistive forced to resist the change. The change being falling. So it's going to resist the change of how to profit backup, right.
Marc De Benedetti: And you'll see here that it actually falls in slow motion and it falls at a constant speed because it's hitting terminal velocity. So let's have a look see
Marc De Benedetti: So there's no sound to the video, but I'll try to narrow you seen it a few times. So here he's dropping it in a different direction. So we dropped it sideways, there's no change in flux.
Marc De Benedetti: But when it falls. Actually, I'm going to pause this temporarily. So what's happening here is when it falls.
Marc De Benedetti: When it falls down the magnetic field lines. Look, it's an electromagnet so they look like a bar magnet. They're coming through this way.
Marc De Benedetti: Okay, so when when the block falls down like this, then what you're doing is you're not changing the area of the, of the, whatever.
Marc De Benedetti: You're not changing the strength of the field. What you're manipulating here is you're manipulating the angle and as it falls. You know when when when the block looks like this.
Marc De Benedetti: Then you only have one or two field lines going through it. But when when the block is sort of up right
Marc De Benedetti: Like we see here. Then we have all of the field lines going through it so that angle that change an angle.
Marc De Benedetti: Changes. How many field lines are going through it and then that's what you get Faraday's law from Ferris law kicks in and then you get an induced current in such a in such a way that opposes the motion, however.
Marc De Benedetti: You just saw here in the video that he had it on its side. He had the short side.
Marc De Benedetti: And he let it full sideways. Okay, instead of forwards. He's he let it fall sideways. Now the reason why that fell really quickly in the video is because if you again, if you look at the field lines, the field lines are coming through and as it falls sideways.
Marc De Benedetti: Or maybe you'll draw it and dotted line as it falls sideways.
Marc De Benedetti: Okay. You still have the same number of field lines going through the surface. So even though it's moving through
Marc De Benedetti: It's the same number of field lines are passing through that that cross sectional area. So there is, there isn't that induced eddy currents and there isn't that resistive force and it falls pretty quickly. I'm going to resume it again and we can keep looking.
Marc De Benedetti: So here he's holding it off center now and without a magnetic field that would just fall
Marc De Benedetti: Here again, it's on a bit of an angle falling forwards.
Marc De Benedetti: So you've got those magnetic field lines coming straight out parallel and as the angle is changing, you're changing the number of field lines. So you're inducing a backwards current you can see here it's falling up mostly a constant.
Marc De Benedetti: Mostly a constant velocity because that's terminal velocity because it's such a strong magnetic field. You don't really need a very fast moving
Marc De Benedetti: Very fast moving object to induce such a strong current
Marc De Benedetti: There is going to do on site again and the site falls pretty quickly, right, because as it's falling sideways, you're not changing the flux
Marc De Benedetti: Okay, now this video goes on for many minutes just repeating the same thing. So we don't have to watch the whole thing. But I think it's cool.
Marc De Benedetti: I think it'd be very cool to have access to an MRI machine and I mean obviously for the medical benefits, but
Marc De Benedetti: Even for the physics, I think, you know, a physicist would would would probably break an MRI machine pretty fast because we would we would just be using it for fun little things like that.
Marc De Benedetti: Okay, so let's move on. We've done enough concepts for at least momentarily. Let's talk about applications of this
Marc De Benedetti: Because I would say Faraday's Law is probably the one thing in first, your physics both 136 and 37 maybe aside from classical mechanics, like cars and the physics of a car and driving stuff like that but
Marc De Benedetti: Faraday's Law is probably one of the most commonly used things in the real world and you have absolutely no idea that it's fair is law.
Marc De Benedetti: Governing what what that cool that cool new gadget is. So one example is is induction cooktops these came out maybe about 10 years ago and Orleans became
Marc De Benedetti: Mass consumable about 10 years ago.
Marc De Benedetti: Where they advertised. Oh look, you can be cooking, you know, boiling pot of water, you can move the pot of water away and Touch, touch the stove, talk with your hand immediately and you wouldn't get burned. Who safe.
Marc De Benedetti: You know, that is called an induction cooktop, and that is that it uses Faraday's law to to work. So what happens, they work well. The basic premise is underneath.
Marc De Benedetti: Underneath that region, instead of a heating element which is usually what you get on the stove is
Marc De Benedetti: A piece of metal that has a very high resistance, you're pumping a huge amount of current through it glows red and it heats up, it heats up because of the resistance, just like a light bulb.
Marc De Benedetti: And that's how the heat gets to the pot and cook your food and induction cooktop however works, not through
Marc De Benedetti: Conduction not through like literally having a metal pan touching a hot other piece of metal. This works through eddy currents. So what happened here is you have
Marc De Benedetti: A coil underneath there and you have an electricity that runs through the coil. Now, when there's a courage traveling through the coil. We know that it will induce the field.
Marc De Benedetti: And the field will look a lot like what what is drawn here to look like a bar magnet. Now, if you put a metal pan or pot.
Marc De Benedetti: directly on top of this coil, then the bottom of that metal pan will be exposed to let me try that in different color will be exposed to the top end of that be field now.
Marc De Benedetti: We have to have a changing flux. If you just place the pan on there and leave it then. Although the bottom of the pan is experiencing a non zero flux, it's not changing. It's a constant flux
Marc De Benedetti: So you can't just have a battery hooked up to this, it has to be an alternating current
Marc De Benedetti: And what we have in our homes is that alternating current AC current. Now we haven't talked about AC cards in this class, nor will we really
Marc De Benedetti: Will talk about a little bit in the in the coming lecture slides and maybe tomorrow.
Marc De Benedetti: But we won't talk about the hardcore math all levels you need encourages it's a DC current that just slipped back and forth.
Marc De Benedetti: So the current of traveling clockwise and then the current struggling counterclockwise and then it's traveling clockwise and then traveling counterclockwise
Marc De Benedetti: And it flows back and forth, back and forth, back and forth. That's what alternating it just direct current that keeps flipping direction, back and forth, left to right now in Canada or in North America, it flips back and forth 60 times per second. So we call that 60 hertz.
Marc De Benedetti: In Europe, it travels back and forth a different number of times per second and off the top of my head. I can't remember what it is, but it's it's not 60
Marc De Benedetti: So that's why when you go to Europe, you need that adapter, because the adapter helps convert
Marc De Benedetti: Their electrical grid with the 240 volts. INSTEAD OF HUNDRED AND 20 and their frequency of alternating current compared to ours and you need that circuitry to sort of
Marc De Benedetti: Force, the current to behave in such a way that our electrical devices can use the power without damaging them anyway. That aside, here we have, if we have an alternating current than the magnetic field switches between going this direction to
Marc De Benedetti: This direction 60 times a second. And that is a changing flux 60 times a second. That's changing pretty quickly. So you have all of the magnetic field going down in in one moment in time, and then a very, very, very brief moment later.
Marc De Benedetti: We have the magnetic field lines traveling up and it keeps switching like that 60 times a second. So federal law kicks in and says, this is a change in flux, and it will induce eddy currents, as you see here, it will induce little tiny circular eddy currents in the bottom of your pot and
Marc De Benedetti: There is resistance in metal and when there's a current V equals I RV from Faraday's law or or electric motor for sure Faraday's law.
Marc De Benedetti: Are the resistance of the metal in the pot itself. So, and then current. So you're going to get a current, you're going to get resistance. And we've already analyzed.
Marc De Benedetti: You know energy equals power times time. So the longer you have the pot on the more jewels.
Marc De Benedetti: as as as the length of time of the pot is allowed to cook the more jewels of energy, you are able to impose into the food and that is how
Marc De Benedetti: You can get heat from the bottom of the pan without having the cooktop itself hot because it's not through conduction. It's through induction, which is really, really cool.
Marc De Benedetti: Now that also begs the question, can you do this with any pot. And for those of you who have induction cooktop at home. You'll, you'll realize or you may be asking me, but Mark, you can't just do that with any old mega with with any old metal pot and all pots are no
Marc De Benedetti: No, look at the mechanism by which the heat is generated. It's through the resistance in the bottom right. So if you have a, you know,
Marc De Benedetti: A thin pot, then you're not necessarily going to have enough material to generate enough heat to, you know, for this eddy current to produce enough heat into the food.
Marc De Benedetti: So if you notice, if you have special induction cookware, you'll notice that there's an extra thick piece of metal that is sort of, well, did to the bottom of the pot. You'll notice this if you even if you google if you Africa lecture. If you want you can Google on
Marc De Benedetti: I mean know where you would buy online Walmart, I don't know, Google induction pots and use the or Amazon and I guess would be a safer bet you can definitely see one on Amazon.
Marc De Benedetti: You can zoom into the picture. And you'll see the bottom of the pot of extra fit compared to a normal a normal pan and they need that extra metal there because they're trying to take advantage of the resistance to to generate enough heat to transfer to the food.
Marc De Benedetti: Another application of area of law that's been around for aeons well before induction cooktops is metal detectors. You know, you might be more familiar with metal detectors that say the airport.
Marc De Benedetti: Or you know you have those new those new ones. We have to, you know, stay with the hands above your head or whatever. Those aren't quite metal detector. They use something similar, but slightly different
Marc De Benedetti: But anyway, maybe you use these at the beach, you know, you can buy a metal detector on a pole and
Marc De Benedetti: And find some very treasure in the sand. This is also working on the principle of Faraday's law. What happens in metal detectors is there is a source current
Marc De Benedetti: You know, it's like with with a battery and this what this does is this generates the source current generates the here's the source current here.
Marc De Benedetti: So using your right hand rule, we see that the magnetic field will look like. Down, down, down. So the magnetic field as you see here in the picture at the center of the loop of all facing down.
Marc De Benedetti: And what you're doing. If you've to sweep it. You got to move and sweep the end of your metal detector. If you just hold them at metal detector stationary over piece of metal, you won't notice it.
Marc De Benedetti: So what's happening here is you're sweeping this metal detector across a piece of metal. So what happens is
Marc De Benedetti: The, the magnetic field lines from the metal detector are being swept across it. So, you know, here you have a full flux and then maybe a moment later in time.
Marc De Benedetti: Your, your, your head of your the head of your metal detector is maybe say over here and all your field lines are over here and then the flux is zero.
Marc De Benedetti: Well, that's the flux changes between the maximum to zero. It's going to induce and any current in this thing.
Marc De Benedetti: And that that eddy currents is is still a current it's a physical current there are electrons that are actually moving and that any current within itself will induce its own the field. So this is the prime be prime being be induced
Marc De Benedetti: And this this induced be field is being felt by this thing.
Marc De Benedetti: And that that's a changing flux through this loop. So then we have a second instance of Faraday's law because this loop fields of changing flux and then we have its own induced current
Marc De Benedetti: And that own induced current can be felt and sense by the circuitry in the metal detector itself and say, oh, I'm detecting a back EMF I'm detecting an eddy current in my, in my own loop.
Marc De Benedetti: And then that's what it sounds the alarm BB BB bb. There's a piece of metal here. So really, what about detector is doing is it's reacting to the magnetic field produced by the any current when you're sweeping the head across a piece of metal.
Marc De Benedetti: And something very similar happens in an airport. If you stand stationary in a metal detector.
Marc De Benedetti: You will notice anything. So that's why they they pause you at an airport. They say wait there. And then when you're ready, they wave us through and you have to walk.
Marc De Benedetti: Through. You can't just pause in the metal detector. They wave you on through, because you have to motion and you need that velocity to have and that philosophy will have that changing
Marc De Benedetti: That changing flux through your body and if you have a piece of metal on you. It will induce an eddy current and then that eddy currents will then feel everything else, so that's that's that's really cool. I think
Marc De Benedetti: And you can actually sort of
Marc De Benedetti: The more physics, you know, you can actually sort of get around metal detectors, if you if you really know the physics.
Marc De Benedetti: Because you know once you know the ins and outs of magnetism and what can cause and deuce currents and how the metal detector work, you can
Marc De Benedetti: You know, you can try to shield it and stuff like that. And it's just, it's really cool.
Marc De Benedetti: You know, instead of walk them. The faster you walk through a metal detector, the easier than metal detector can detect metal. Right. So the other. The other thing you can do is you can try walking through a little bit slower, you know, all these other sorts of fun things
Marc De Benedetti: Okay, so here's an example. Um, I don't know if we have time to do this at the moment. So we might come back tomorrow at the beginning of lecture to do this.
Marc De Benedetti: There's a bunch of problems here that I've included I don't necessarily intend to do all of them and lecture. Some of them here. I even put the solution. So I might tomorrow, I might do some of the ones that don't have a solution like like this one here.
Marc De Benedetti: But we definitely don't have time to lecture to do all of them, but maybe tomorrow is a bit of a refresher for what we talked about today.
Marc De Benedetti: However, there's one last thing I want to start talking about today. We'll finish talking about tomorrow is generators. So I mentioned at the beginning of this lecture. If you recall,
Marc De Benedetti: You recall we had an example where we had a square loop of wire that was inside
Marc De Benedetti: A uniform be field and we were pulling this wire this loop of wire out
Marc De Benedetti: And we noticed that our mechanical energy of pulling the wire was able to induce occurrence. Now we've been talking all lecture about this, but that was sort of the first exposure we kind of had to that sort of nifty idea.
Marc De Benedetti: And I told you that that was sort of the basis of a generator. So let's actually come back to that now and will formally talk about generators. So what is a generator
Marc De Benedetti: Well, in terms of physics all a generator is is a mechanism by which we can take advantage of converting mechanical energy, which we have readily available into electrical energy, which would be a current. So you a generator could be
Marc De Benedetti: Like like turning the crank. You know the old cars from like the early 1900s. To start the car.
Marc De Benedetti: You know you had to go up to the front. There was a crank on the front of the card to determine the crank to start the car.
Marc De Benedetti: That would be a form of a generator right you're you're converting mechanical energy into electrical potential energy and the gasoline this the picture here on the slide is an example of a modern looking
Marc De Benedetti: Gasoline generator where you pour gas in gas takes the place of your arm and it physically moves this this loop of wire through a magnetic field and using Faraday's law this generator can produce and generate electricity.
Marc De Benedetti: Now that's pretty much all there is to it. In all honesty, but here are some schematics so buried within the generator
Marc De Benedetti: Yes, there's gasoline. There's a gasoline engine because you know you want to automate the the mechanical energy. You don't want to be sitting here yourself doing this but anyway.
Marc De Benedetti: That aside, what's actually happening is you have a loop of wire. Okay. In the generator and the loop of wire is is connected to a shaft
Marc De Benedetti: It's connected to a shaft. You can't see the green on the black is connected to all that much better connected to the chef and the shaft is rotated either by your arm or, I guess, in the case of a gasoline generator rotated by the gasoline engine.
Marc De Benedetti: Now what's happening here is there is a permanent magnet inside. Sorry. Inside the generator and what's happening here is the loop is within the permanent magnet.
Marc De Benedetti: And when you have the shaft that connected to the gasoline engine, the shaft physically rotates the loop and there is, I don't know how to draw this very well.
Marc De Benedetti: There is some sort of permanent magnet around here will say permanent magnet.
Marc De Benedetti: And that's where, that's where this magnetic field is coming from. It's coming from the permanent magnet if you if you want to you can think of it like a U shaped magnet if you if you want to
Marc De Benedetti: And the coil inside is physically and forcefully being rotated within the magnetic field. So,
Marc De Benedetti: In which direction we know fairly laws gonna kick in, in which direction is the induced current going to be well we think to ourselves, okay.
Marc De Benedetti: We know flux is be a coast theta which factor is a is a gasoline generator taking advantage of to generate electricity.
Marc De Benedetti: Well, it's using a permanent magnet. So it's not taking advantage of changing the magnetic field strength because it's a it's a permanent magnet. It is what it is.
Marc De Benedetti: Are we changing the area of the loop. Nope. The area of the loop is is buried inside we have no ability to change it. So that's not what we're taking advantage of
Marc De Benedetti: We are taking advantage, however, of the angle between the be field and the area vector, the normal to the to the face of the loop.
Marc De Benedetti: So at the moment in this picture as as an example that the field is traveling or directed horizontally. So, at this moment in time, there is no flux through the loop that all field lines are passing over the loop, not through the loop. Now if you crank it
Marc De Benedetti: Forcefully crank it in this direction, as indicated here, then at a moment in time later, the loop is going to be
Marc De Benedetti: Up at a bit of an angle so five two is going to be greater than zero, we are increasing the number of field lines.
Marc De Benedetti: Increasing the number of field lines through the loop now fairies law or I should say lenses law says the induced current we want to oppose that.
Marc De Benedetti: We are increasing the number of field lines through the loop. We want to decrease the number of field lines for the loop. So that means the induced be field would be. Now if we if we drew the loop like up right like this.
Marc De Benedetti: We would want to have an induced to be field backwards be induced backwards and use your right hand rule, thumb backwards and and curl your fingers and you see the current would look like this. So the current would look like this.
Marc De Benedetti: In the loop, given that this is the direction in which we are rotating it
Marc De Benedetti: Okay, so that's how a generator works. Now, for those of you who don't have cottages or don't know that hospitals have generators, you know, many of you will think that you don't have you've never seen a generator in action before but you have
Marc De Benedetti: It's called an alternator, you know, your car has batteries and why does a car have a battery. Well, back in the early 1900s.
Marc De Benedetti: Well, you need a spark to burn to burn the gasoline right that spark used to come from the spark plug. And where did that spark come from well in the good old days of 1920s.
Marc De Benedetti: When you want to start your car, you would crank it with your own arm and you would you would crank this this loop.
Marc De Benedetti: In a magnet and that would generate a current while your arm was forcefully turning this coil a magnet and it was hard to do. It was very hard to do because there's up there's that back EMF that you're feeling
Marc De Benedetti: And so it was really hard to start to start the car, especially in the wintertime in Canada. Anyway, that's a different story.
Marc De Benedetti: So you need this, you need this this this source of energy for the spark plugs. Now once the car was started, there was an alternator.
Marc De Benedetti: Okay, so once the car was started the engine with burning gasoline and to get it to the canvas source of mechanical energy, and in addition to pulling the car forward. The the
Marc De Benedetti: The car would have the engine would also spin something called an alternator. So you see here, there's actually a mess of coils here just a huge rat's nest of coils.
Marc De Benedetti: All this is is just a very, very well thought out way to wrap very efficiently as many loops of wire as they can in a limited amount of space. So they didn't just do it messily and haphazardly they they did it in a very logical way.
Marc De Benedetti: And what they're doing here is there is a permanent magnet. As you can see here, and the gasoline engine once once it got started it. It was spinning this magnet, this, this.
Marc De Benedetti: loop of wire mess of loops of wire in this magnetic field and it was then providing the energy for the spark plugs.
Marc De Benedetti: To continue to continue delivering the spark. It needs to ignite the gas to continue to run the alternator. It's just a well oiled machine, quite literally, a well oiled machine. It's, it's, it's a perfect balance of physics.
Marc De Benedetti: And you might be thinking, well, you know, it sounds like you know a free energy machine like along with the engines rolling the alternator can spin and can you know power the
Marc De Benedetti: Spark Plugs which can continue the engine rolling. Yes, that's what's happening. But again, there's no such thing as a free lunch.
Marc De Benedetti: You know there's friction in the system. There's combustion. So you're losing some energy do the heat.
Marc De Benedetti: You know there's resistance in the wires. So, you know, you can't just get the engine moving and then it's forever moving
Marc De Benedetti: You're constantly having to speed it mechanical power by burning gasoline. So, you know, there is no such thing as a free lunch. How is it getting this power by burning continually burning gasoline and that's, that's why it's to fill up on the gas every now and then.
Marc De Benedetti: Now, since the 1920s, we've developed batteries car batteries well all batteries, but specifically car batteries in this case. So instead of having to crank your car now in modern time
Marc De Benedetti: We use battery. So the battery is, you know, in the engine compartment of your car and it takes the place of of you actually cranking the engine. So your car has something called a starter and the starter is literally a DC motor. So your car has a starter.
Marc De Benedetti: And if you don't believe me, you can Google. You can google like starter for a car or a lawn mower or whatever. And all this is is it's a DC motor
Marc De Benedetti: And it mimics your arm cranking the engine. It's literally with a set of gears.
Marc De Benedetti: Is connected. There's a fly wheel that comes out when you when you turn the key in your cards on the fly wheel from the start of that comes out that connects to the engine.
Marc De Benedetti: And then the battery in your car. I think it's a 12 volt battery. So it's not even a super high voltage of
Marc De Benedetti: The battery in your car will will run the DC motor and the starter and artificially cranks the engine and then your battery will also simultaneously provide the power for the spark plugs.
Marc De Benedetti: And then once your car is running it moves the alternator and the alternator will provide the power for your car stereo your headlights your horn, the spark plugs and everything else and your air conditioning.
Marc De Benedetti: Now here's the question though. Why do you only have to link like you have to turn your phone almost on a daily basis, you know, using your phone, your battery dies.
Marc De Benedetti: Why do you only have to change the car battery once every like three or four years.
Marc De Benedetti: Well, because as the car is running the alternator will charge the battery. So it's this really nice marriage of, of, you know, converting chemical potential energy like gasoline.
Marc De Benedetti: Into electrical potential energy and that marriage is done through Faraday's Law. It's really, really quite beautiful. And that's why if you use, like if you go to a drive in theater.
Marc De Benedetti: Not, you know, like, you know, you're sitting in your car, your engines OFF AND YOUR, YOU'VE GOT YOUR STEREO on
Marc De Benedetti: They add intermission, there's always a sign or a little ad that comes up that says, you know, during the intermission, everyone. Turn on your car and let it run for 10 minutes
Marc De Benedetti: And, you know, I've literally heard people say, well, that's just a waste of gas that's just stupid. Why are they saying that
Marc De Benedetti: Well, they're saying that because if your car is and running your, your car stereo is running on your car battery.
Marc De Benedetti: And nothing's charging your car battery and what they would hate for you to do is at the end of the movie, your, your battery is so dead. It doesn't have enough juice to turn your car engine.
Marc De Benedetti: So they tell you at intermission to turn on your car so you can spend 1520 minutes charging the battery in your car now as a quick side note about cars.
Marc De Benedetti: I drive a standard I don't drive an automatic I drive a standard and I only drive when I drive standard for two reasons. I like to have total control over my two ton piece of self perpetuating death metal
Marc De Benedetti: You know, a car is effectively a weapon on the road and I personally want to be in total control of that weapon at 100% of the time.
Marc De Benedetti: So I don't like an automatic transmission telling me what I can and cannot do with my car.
Marc De Benedetti: That's one reason why driver standard. The other reason why a driver standard is because
Marc De Benedetti: You can actually pop the clutch to to turn the motor of the car and this happened to me once I've actually at the drive in once about three years ago.
Marc De Benedetti: And I didn't realize that my battery was getting old and it was needing to be changed, and I just didn't realize and my car didn't start after after the movie.
Marc De Benedetti: And luckily for me. I was able to use the kinetic energy of my car, you're, you're always parked on a little bit of a hill, when you're watching
Marc De Benedetti: When you're watching them drive in theater.
Marc De Benedetti: So the car itself was on a bit of an incline about three or four degree incline.
Marc De Benedetti: So what I did was I left the car took the brakes off and I left the car roll backwards and I pop the clutch, you know, the car had momentum. The car had velocity. I had kinetic energy.
Marc De Benedetti: And when I engage the clutch I connected the engine with the tires and I stole the kinetic energy of the car and I used to connect energy of the car in, in, in place of the starter or in place of the battery and it was able to
Marc De Benedetti: Turn the engine over once and that's all it needed to have one spark of the spark plug.
Marc De Benedetti: to ignite the gas and you can start the car that way. And then as I drove home and it turns the battery. And then a few few days later I replace the batteries, I realized it was getting old, so two reasons why physicist should always drive a clutch.
Romina Piunno: A lot more fun.
Marc De Benedetti: Oh, they're also a lot more fun to oh yeah we also drive a stick. I should have. I knew that I should have mentioned that. So I don't know will hurt her dad's her does not a physicist and her dad also drives a stick, so maybe there are other reasons why she drives a standard, but anyway.
Marc De Benedetti: The other. I was gonna say something else. Oh.
Marc De Benedetti: There is one type of automatic transmission that I will lovingly drive, not just begrudgingly drive if you have an electric car. Let's say like a Tesla.
Marc De Benedetti: Tesla doesn't have any transmission, quite frankly, a Tesla. It has its motors instead of a gasoline motor has an electric motor and each tire looks the engine on each tire looks a lot like an alternator actually
Marc De Benedetti: Each tire has its own DC motor in each tire has its own mess of coils and it we pump current through from the battery. And when you pump current through a coil. We get to work on the coil. We've already talked about that previously torque on a coil. Remember to work on coil. Was I a bee.
Marc De Benedetti: So you get to work on this coil and it actually, that's what rotates the tires forward. So there is no clutch. There is no in there's no, there's nothing in between me and the tire is still with an electric car it's you and then the tire.
Marc De Benedetti: You know with it with an automatic transmission. You know, there are times when you want to go accelerate and then your engine doesn't respond because there's a bunch of
Marc De Benedetti: moving parts underneath your car that's automated and you know you wanted to do something that doesn't right away and it's really frustrating.
Marc De Benedetti: So anyway, with an electric car it's, there's still nothing. We'd like there is nothing automated. There's no gears. If you want to go faster. You just deliver more current
Marc De Benedetti: To to the to the to the motor and then more current means more torque which means faster movement. It's pretty simple. And you might ask yourself, well, how do you turn the car on on
Marc De Benedetti: Well, how do you charge the battery electric car. Yes, you have to charge it more frequently people with a Tesla right now. I think you can get up to maybe 200 kilometers before to recharge the battery.
Marc De Benedetti: But the way they sort of elongate that span is with the brakes instead of brake pads, where you squeeze you squeeze the tires. They use
Marc De Benedetti: What they do partially that as well. In case you need to stop really quickly, but they use magnetic breaking
Marc De Benedetti: When you break they they turn the DC motor into a generator when they break instead of feeding current to the DC motor they stopped the current from battery when you push on the break.
Marc De Benedetti: And what they do is they they use the rotation of the tire as as a generator to spin the coil inside the magnet.
Marc De Benedetti: And that creates a back EMF which charge the battery. So in a Tesla every time you break you are partially charging the battery. So again, this marriage of
Marc De Benedetti: Of old technology and new technology, but it's based on the same physics, whether you have a company internal combustion engine, it's, there's still a lot of fairies law in it. And if you have a Tesla. It's just a newer shiny version of a car.
Marc De Benedetti: And and instead of burning gasoline you're using up stored chemical charging the battery, but you still have the sort of marriage of DC motors and Faraday's law. So I just
Marc De Benedetti: There are so much physics that goes into a car and just it's mind blowing, how cool it is like
Marc De Benedetti: You know, there's the physics of driving and the friction pulling the car forward and some triple motion when you turn a corner and
Marc De Benedetti: Torque when you want to flip a car and bankers and you go on the highway, like all the classical physics. And then there's there's a modern physics in a car that's just remarkably cool absolutely remarkably cool
Marc De Benedetti: Okay, so I don't want to jump into transformers just yet because that's a whole new that's a whole new topic and there's
Marc De Benedetti: There's quite a lot to that topic and in five minutes, it would not be, it would not be appropriate to sort of start a topic and then stop. So, and that's a stopping point would be the end of generators
Marc De Benedetti: The only thing I really expect students to really understand from a generator is. Well, I mean, for one, the underlying physics is Faraday's law so
Marc De Benedetti: You know, what can you do with generators. What kind of homework questions can you do with generators
Marc De Benedetti: You know all a generator is is just a loop of wire that is being rotated through magnetic field. So, the equation, you're still dealing with is fair day's law be a coach theta or I should say the derivative of BA coast data. So, you know, you can talk about, you know, the faster the faster.
Marc De Benedetti: The faster rotation rate, the more voltage is going to be generated. The more loops, you have, the more voltage is going to be generated.
Marc De Benedetti: So generators. Like there's nothing new, with a generator. There's no new physics is no week no new equation with a generator. The only thing new is the application, right, it's all the same physics.
Marc De Benedetti: The chapter of generators is merely an example of how we can use Faraday's law to our human advantage.
Marc De Benedetti: And how if you know physics, you can actually manipulate nature around you to to do your bidding, which is actually a really if that doesn't convince you to be a physicist, I really don't know what else could
Marc De Benedetti: You know when you actually know physics, you can manipulate everything around you to to make your life easier. That's really the the fun part of it being a physicist.
Marc De Benedetti: Okay, so that's enough for today, we're a few minutes early, which is OK. So I'm going to stop the recording. But then I'm going to hang on the line. And I'm going to take any questions that
Marc De Benedetti: That students may have. Okay, so if you're watching on YouTube. I will see you tomorrow. And we will pick it up with an example of ferreted law that we skipped earlier. And then we're going to resume it with transformers. Okay. Ciao for now.
