Hello scholars, I'm Dr. Hebert. In this video we're going to be discussing electricity and magnetism. And the core concept behind this video is that electric and magnetic fields interact and can produce forces. So we're going to discuss the atom in a lot of detail in chapters 8 and 9 later in this course.
And I just wanted to... present to you a very simple electron cloud model version of the atom. It's kind of a revised Bohr model where we have in the nucleus of an atom positive and neutral charges, a proton and a neutron, and so the overall charge of a nucleus is positive and surrounding the nucleus are electrons and those are negatively charged. And that's all we're going to discuss for this chapter, but we will hit that in way more detail when we do the atom in chapter 9. And we'll move on to static electricity. So a lot of you have experience with static electricity either walking across the floor in some slippers or wool socks and then you touch a doorknob and get shocked or static clinging when you pull your clothes out of the dryer or if you're brushing or combing your hair and you feel the static charge as well.
And what happens is hair and the comb are neutrally charged. They have both protons and... Electrons mix throughout and so they end up being neutral because positives attract negatives. So opposite charges attract. But as the person in the image brushes their hair, they're going to transfer electrons from the hair to the brush through friction.
And eventually that can build up. Well, that'll build up a charge and can lead to static electricity between them. So there's a couple of methods for charging.
Of course, we just talked about friction here with the comb. It can also just be by conduction with direct contact and also induction. And this is a polarization process where basically if you have...
net negative charge on the comb, what happens is it draws all the positive charges from another object to it and it induces a charge. And so that would be called induction and that's an induced charge. There's a quiz question about static electricity featuring lightning and there's a couple of things going on here and I was reviewing the quiz question and when I wrote it I It made sense to me and then I went back and reviewed it and it's actually a little more complex. So I'm going to make it simple.
The question is regarding charge and a cumulonimbus cloud and how did these charges separate? So how did all the positive charges get up here and all the negative charges down here? And as the air moves around, that's that frictional method of charge. So it's friction of the air molecules it's going to remove and separate the charges out. So what I'm hoping you pick on the quiz is friction.
So the positive charges go up here, the negative charges go down there, and that's from friction. Now lightning would result from cloud to ground because of induction. You get an induced charge.
What happens is you have positive and negative charges in the ground, but because you have this negatively charged air mass right above it, it's going to kind of pull the positive charges. Now the air has resistance, so it's not a closed circuit. But however, if the charge gets strong enough, then what happens is you get lightning. And that's cloud to ground lightning.
You can also have cloud to cloud lightning. going from opposite charges that way. You would not get lightning between like charges. So that's not going to produce lightning. But the answer we're looking for in that quiz is that the charges in the clouds come from friction of moving air molecules.
In order to conduct electricity, there are different materials that you can use and conductors are materials that conduct electricity really well and insulators actually prevent that. So if you have a copper wire, one of the things you can do to protect yourself from electrical current is put it and a jacket that's insulated. That way you don't have to worry about it and then you have your leads at the end.
So, electrons move freely through conductors. Gold, silver, copper, those are all really good conductors. And things that don't conduct well are called insulators and things that kind of conduct are called semiconductors.
Chapter 6, sections 3 and 4 and 5 talk about charge. And while I probably should be talking about electric charges and coulombs, which is the SI unit for charge, I'm going to skip this for a more advanced physics class. It's not that big of a deal to go ahead and go into it, but this chapter has so much material that I'm going to go ahead and skip those sections on electric charge and forces from those charges.
I do want to talk about magnetic force fields and electric fields. And here we see electric field lines, and this is very similar to a magnetic field line. When you have opposites, consider this to be sort of like analogous to a bar magnet that has north and south poles. And these are the field lines that you would see, and they're strongest right here at the poles. That's where the field lines are going to be the strongest, where they're closest together.
So at each of the poles, they're the strongest. So, strongest at polls. And I think there might be a quiz question about that.
You might be thinking I'm feeding you a lot of quiz items. I'm trying to encourage a little bit more viewing of videos. So, stay tuned for some more hints. Obviously, if you have like polls, then they are going to repel one another.
And so, those field lines are shown there. And you could see this easily with a bar magnet. put a piece of paper over it, and drop some iron filings, and they will reveal the field lines pretty nicely. Okay, so electricity will move, and it flows, and we're going to describe that electricity flow through its current and its voltage.
So we're going to look at current, which is measured in amps, and it's represented with a capital I. And the unit for current are amperes, but we just say amps for short. And voltage, capital V, and that's also the unit volts.
And those are the symbols that we'll use. So when you're looking at an electric circuit and you're looking at voltage and current, You know, the conventional method for describing this is using sort of two different reservoirs, a lower reservoir, an upper reservoir, a paddle wheel. But I find it to be a little bit easier to explain, at least my middle schoolers would say so, if we look at pipes and water flow through the pipes. So let's say we have a pipe that's a very large diameter. and a pipe that's a very small diameter.
And that would be analogous to voltage. So this would be high voltage because it's a large pipe, and this would be a low voltage because it's a little pipe. Current would refer to how fast the water moves through.
So if we turn the hose bib on and we just have a little trickle, we've got a large voltage but very little current. We can also do that with a little pipe and have a little very little current through very little voltage, but you can also if I turn this hose bib all the way open if I turn it all you're going to get a lot of flow through here and you're going to get a lot of flow through here. So you get high current and a low voltage and you get you know high current and high voltage and what happens is the flow.
of the water is related to the current. Current is what you really need to be afraid of when handling electricity. A lot of the times it's not the voltage that's the problem.
It's the current that's flowing through. So if I aimed a fire hose at you and I just opened up the hydrant a quarter turn, the fire hose is not intimidating. It's not going to hurt you. So having a large pipe or a large hose not going to be as dangerous as the flow of current through that and that's the same with electricity so obviously if I open that hydrant all the way open the fire hose becomes very deadly and dangerous towards you if I aimed it at you We're going to skip a little bit of the math on this regarding charge, which I already mentioned earlier.
However, we do need to talk about Ohm's Law. So we are going to see one to two math problems on the quiz involving Ohm's Law. And it might be that you're solving for voltage given current and resistance. And it could be that you're solving for current. if you're given voltage and resistance.
So capital R is resistance and it's exactly that. It's a resistor is something that slows down the current. So if I have a garden hose and I've got the open all the way and it's spewing out water or electricity in the metaphor, a resistor would be like kinking the hose or putting a nozzle on there and that's going to slow down the flow. So a resistor is going to limit how much Electricity is going to flow through that circuit. The unit is ohms and the symbol is the Omega symbol here.
And so you're going to, if I give you the current or the resistance, you should be able to calculate the voltage. It's just V equals IR. You could also say R equals V over I.
These are the three ways you can express Ohm's law, and it relates current and voltage with resistance. So let's just do a couple of practice problems because I've had some student requests to do more examples in the videos of the kinds of math problems that you'll see. These aren't terribly complex as they won't be on your quiz.
In fact, I got this out of, well, I shouldn't say that I got it out of a middle school science textbook, but... I don't want to humiliate anyone. So here you're asked to find the voltage if the current is 2 amps, excuse me, 0.2 amps, 200 milliamps, and the resistance is 2 ohms. So if you just remember V equals IR, you plug the current for amps at 0.2, the resistance is 2, and you get voltage is 0.4 volts.
So that's your final answer. However, what if they ask for, they give you the resistance, oh this is the same problem as the first one, they're asking you to get the voltage. So if you have 9 amps and 4 ohms, then obviously you're going to get 36 volts.
Now, all three of these examples have you calculating voltage. What if they said an object has... 20 amps, excuse me 20 ohms and Let's say you're operating something at 5 volts. What's the current that's going to draw through that circuit? so if the voltage is 5 and Resistance is 20 ohms.
Then what is the current and amps going to be and so if you remember V equals IR Then you should be able to solve for current V over R equals I Excuse me. I was just rearranging the equation. And so you would just get the voltage 5 and the resistance 20 and 0.25 amps, 250 milliamps.
So, you know, it's not complex math. It's just single step, single variable equations. A little more on resistance. You can use different materials that will resist conductivity. Temperature also affects it too, so you have to consider that.
This is something that would probably be a little more relevant to you guys, but I'm not going to have you do any math problems. This is a calculation for power given current and voltage. So it's really simple. Do you all remember the units for power?
The unit was in watts. And so you can get power, electrical power, by multiplying voltage times the current. And one of the things that's really interesting is looking at light bulbs. And something that we've been doing in our home for a couple of years now is monitoring the energy or the energy bill.
And we've been looking at experimenting with LED bulbs, incandescent bulbs, and compact fluorescent bulbs. And so I have a 60 watt incandescent light bulb. Those are the kind that produce a lot of heat.
And of course they're running 120 volts or 110 volts. through our home's power system. So you can calculate the amps or the current using this equation.
What's really interesting is that the LED bulbs only draw about 4 watts of energy and yet they're getting the same voltage in. And so what would what must that say if we're dropping the power down but we have the same voltage, what does that say about the current? You're drawing way less current. It's not going to cost as much money because your bill is going to go down.
Now, are LED bulbs more expensive on the front end? Absolutely. But it doesn't take long before you recoup that cost and start saving some money.
Okay, so electricity is very closely tied with magnetism. And you're going to see a few examples like electromagnets, generators, motors, transformers, and things like that. speakers and microphones and how electricity and magnetism go together. So, a typical bar magnet here has poles.
So, they are definitely polarized. They've got a North Pole and a South Pole. And, if you were to break this magnet, every single time you break it, it keeps the exact same field line.
So, you would create a new South Pole and a new North Pole. These should look a little familiar from the electric field lines we looked at earlier. One of the things that most people don't realize is that if they're holding a compass and the magnet inside the compass points north, and this is the north end of a magnet, then if we overlay the earth, the magnetic north must be pointing towards the magnetic south pole of the earth.
I just realized that made no sense. So here is America, South America. We've got Europe over here and Africa. This is actually the South Magnetic Pole. And we call it the North Pole.
I don't want to leave out Canada, sorry. So we've got the Magnetic North Pole is actually down in the Geographic South Pole. Because the magnet points, this is the north side of the magnet, it points that direction.
So that's actually the South Pole. Just a little fun fact for the borrowers. Alright, we're going to skip that one and we're going to skip that one.
And there's a picture showing Earth's magnetic field. Incidentally, the magnetic North Pole and magnetic South Pole are not the same as the geographic North and South, and it actually moves. In fact, it's completely swapped several times, and they call it a wobble.
We have to update our navigation charts about every 3 to 5 years because the magnetic field lines change. Alright, so let's take a look at the connection between electricity and magnetism. Here's what we figured out. Well, we didn't figure out. This is Horstead's.
He figured that out. He noticed that when you have an electric current going through a wire, let's say this is a copper wire and there's electrons flowing through, it produces a magnetic field around that wire. That was a huge discovery.
He noticed whenever you got a compass near a wire that had electricity flowing through it, the compass started going crazy and it would change its orientation. Depending on where the compass was, it would point in different directions. It just completely disregarded the magnetic south and north poles of the Earth, because it just got disturbed by the electricity. So, if you're ever using a compass, you want to make sure you're away from electrical wires, because it disturbs the magnetic field. In fact, I have a sensor that I use and some electrical work that I do around the house to make sure that I've got the right breaker turned off.
It's a non-contact... sensor that will tell me if a wire is hot, if there's electricity flowing through it. And it doesn't even have to touch it. What it does is it senses the magnetic field that's generated around the wire. And so if there's no electricity flowing through it, there's no magnetic field generated around it.
So it's a pretty helpful device. And this picture down here shows you how the compass responds when electricity starts flowing in different directions. Here there's no electricity flowing. so the compass points in the same direction, magnetic north, well I guess it would be, or you know the magnetic poles, but if we put the electricity on in this direction, then it changes the compass needle start to go a little bit. Crazy, they'll show you the magnetic field lines around that.
And by the way, this is called the right hand rule. So if you take your right hand and you put your thumb out in the direction of the flow, it shows you the direction of the magnetic field. Okay, you can see here in this picture when we have a wire coil around.
connected to this battery, we create some really strong magnetic field lines around that wire coil. This is going to become really important as we start to look at how motors and generators work. Okay, electromagnets.
We've already discovered that if you hook up a wire into a battery, you generate a magnetic field. So we can actually use that electricity to create a magnet. We call that an electromagnet. So the nice thing about electromagnets as opposed to like a permanent magnet is we can turn them on and off. And so we'll use this in a lot of applications like speakers and microphones, but also, you know, you might be the more famous kind in junkyards or shipping shipyards where they're picking up containers off cargo ships.
They use gigantic electromagnets to pick up the containers or cars. Okay, so there's a couple of things you can do to increase an electromagnet's strength. And you may want to just jot a little list down.
I think there might be a quiz question. One, increase the number of loops in the wire. If you increase the number of loops in the wire, you can actually strengthen the electromagnet.
Two, if you increase the size of the iron core. So basically, if you have like a nail or a metal rod and you put... wire loops around it and connect it to a power supply, that nail inside the wire will become a magnet.
So you can increase the size of that core. If you get a larger nail, then it will be even more powerful magnet. Increase the size of the iron core. And then, of course, if you increase your power supply, your battery, that's going to help too.
If you increase all three of these, then you're going to have a really strong electromagnet. One of the cool things you could do for your lab demonstration, your concept demonstration for 105L, is demonstrate how, if you take different size nails, that you can pick up more paper clips. So take a 9V battery or even a AA battery and some wire leads off that. Loop the wire around the nail. See how many paper clips you can take up.
Using the same number of loops, put it around a bigger nail. You'll see that you can pick up more paper clips. Conversely, if you just use the same nail and then do more loops, you'll pick up more paper clips.
It's a pretty cool experiment. Alright, let's talk about Michael Faraday. Michael Faraday said, through his discovery, that if you hook up an ammeter or a voltmeter, a multimeter, that measures current or voltage, and you have that... wire coil.
If you move a magnet through there, you'll actually drive electrons and get a reading on here. You'll start to generate electricity. This is called electromagnetic induction. This is pretty important because it's how we get electricity in our homes.
So remember when we talked about energy conversions and we talked about the coal burning power plant or wind alternative energy, the generator was the black. box and all of that that it turns a turbine powers a generator and we get electricity this is the generator right here you've got a wire coil and a magnet and by moving the magnet in and out back and forth you start to drive electrons so if we can move that magnet mechanically around the wire coil or we can fix the magnet and move the wire coil around the magnet we're gonna get electrons to flow we're gonna get electricity that that's the electromagnetic induction that's It's pretty awesome. And so that is a generator.
And we've made it a little fancier than just a roll of wire. But basically we have a magnet. We've got the wire coil around there. And the magnet is going to turn the armature.
And basically what's going to happen is we're going to get electrons to flow and move out. we can generate electricity. Okay, one of the last things I want to talk about before we get into circuits are transformers.
You're going to do a really cool lab on transformers. It's more than meets the eye, trust me. They have basically two iron cores.
We loop wires around it and we can step the voltage down or up depending on the number of wire or coils around each primary and secondary loop. So, if this is the primary, this has 10 coils. This only has one on the secondary. So this is going to be a voltage drop. And transformers are really important.
We need them because as power plants send high voltage electricity throughout the grid, you can't run this necessarily straight to your refrigerator. So you need these transformers in your home to drop the voltage. Sometimes they're already built into the appliance.
So the refrigerator plugs into 120 volts, but inside the fridge there's a transformer that's going to drop the voltage to that that's required to run the compressor. So this would be a voltage drop and this is a step up transformer. This can ramp it up so we can take a smaller voltage and then ramp it up.
based on coiling the wires around this. So that's what a transformer is. You're going to be doing a lab on that, as I mentioned.
And it's expressed in different ways. This is the voltage of your primary. This is coming in, and this is going out.
So the voltage of what you want coming in, this is the voltage going out, is proportional to the number of wire coils that you have on the end, to the number of wire coils. going out. So there is a little bit of proportional reasoning that you're going to have to do in your math here, but it's real simple. You just put the voltage in and you get the voltage out.
And let's say we have the number of coils that we're going to do, you know, 10 coils. Sorry, let's make that 12.012. You can just cross multiply or if your proportional reasoning is really strong. So 10 times 12 is 120 divided by 120 is 1. So you only need one loop on the secondary coil. Let that kind of sink in.
Watch it again. Read the chapter and when you do the lab it's going to make a lot more sense when you step up and step down. So there's a couple questions on the quiz. It's going to require you to talk about how to recognize a step up step down transformer.
And your lab will help prepare you well for your quiz on doing the calculations on figuring out how many turns you need to do on each coil. Or if you're given the number of turns on each coil, what the voltage out would be. Let's do a practice problem.
So a transformer has 3,000 loops in its primary coil. So I'm not going to draw 3,000 loops, but let's say that this has a lot. We'll call that 3000. And then we've got 1500 over here.
And that's the number of loops around the secondary coil. What's the voltage in the secondary coil? So we're looking for the voltage over here, voltage in the secondary.
If the primary is 120, and that's standard voltage in your house, generally on your breaker you'll have a couple spots or slots for 220 and that would do like your central air heat, maybe your hot water heater and clothes dryer. Everything else runs off 110, 120. So, we have everything we need. We've got the primary voltage, we've got the number of coils in the primary voltage, we've got the number of coils on the secondary, we just need Vs on the secondary voltage. So, you can set this up as a proportion, 120 volts at 3000 is equal to some unknown. over 1500 and you can just cross multiply and figure that out.
You can simplify this as well and solve for x. So, 1500 times 120 divided by 3000. That's your solution. You can get a calculator and do the math.
We have two kinds of currents that we can send through electrical wires, alternating current and direct current. The reason why we chose alternating current, which goes basically back and forth, is because it can travel over long distances without a lot of loss. Direct current over long lines, you actually lose a lot of the electricity in the current, and there's a huge drop.
And so in the United States of America, we use alternating current on our grid, but most of our devices require direct current. So we would have a transformer or an AC adapter and convert that alternating current to a direct current. For example, your plug in your house runs 120 volts, but your laptop that you're charging might only take 19, and that's direct current.
So you plug in that plug that has the black box in the line, and that's what's going to change your voltage to whatever the appliance needs. Okay. There are two kinds of circuits that we can talk about. Series circuits and parallel circuits.
A series circuit basically has everything in one line. So light bulb, we got here to power, negative to positive, negative to positive, negative to the light bulb and the light bulb is going to go on. Now these are additive.
So if this is 1.5 volts. and this is 1.5 volts and 1.5 volts then the whole system is 4.5 volts when you add these all up so that's in a series you sum all of the power supplies and this light bulb may require four and a half volts to come on if you just did one uh you know a c battery in 1.5 volts it's not going to charge it but if you hook them up in um in a series, then you can get that to come on. A parallel circuit is wired differently. We go negative to negative, negative to negative, through the filament of the light bulb, and then hit all the positives.
And if this is 1.5 volts, and this is 1.5 volts, and similarly down here, You don't add them up because they're not going negative to positive or positive to negative. They're going positive to positive. So what this does is it only has 1.5 volts in this circuit.
However, because there's three batteries, it extends the life of this circuit. So that's another reason why you might want to hook them up this way. It's because instead of draining just one of these very quickly, you've got them all three there and it's going to make it go.
take a lot longer. It's going to make greater electrical energy available. If you want to add multiple devices in that circuit, this is a series circuit. It's still a series connection because everything is in one path.
You can kind of tell going back here, these lines are going in parallel. So that's why they call it parallel. In a series, they're just one after the other.
And so... The problem with series circuits is if this light bulb goes out, then electrons flowing can't get past this point. So what happens to these bulbs?
They may not be broken, but they're not going to shine because the electricity is stopped right here. So this is why the old Christmas lights from a long time ago, if one bulb went out, the whole strand went out because they were wired. Now, a lot of holiday lights are wired in parallel, so if one goes out it just skips that one and goes on to the next one.
By the way, if you have multiple resistors in a circuit, you add up all the resistors to get the total resistance. They're summative, so you can just add them all up for the total. So, here's a typical home wiring. You got a breaker box. And you've got, of course, you've got your load coming in from the power company.
It comes from the transformer outside. It might be a box on the ground or if you live with aerial lines, it would be up on the aerial lines depending on your neighborhood. Ours are all below ground so our transformers are in a big green box on the ground.
And so these are basically big switches for the circuit and you can break the circuit. You're going to send electricity in. You've got a light switch on the wall. That's going to turn the light on, but then you also have all of these power outlets. So these are in parallel and the reason why you want these in parallel is because You don't want to have to pull one out and then all the others not working.
So the idea is that you put these in parallel so that each of these appliances run independently of one another. So you can complete the circuit. Okay, so a lot of information in this video.
Do the reading, pause it, rewind it, watch it again, do the lab, and I think you'll do well on the quiz. As usual, call or text if you have any questions. Thanks!