 So basic circuit concepts part 2 and again today is going to be mostly terminology a little bit of equations We're really going to get into the meat and potatoes in lesson 3 So the fact that I've done two lessons before your test don't freak out Says recall that as charges flow through a circuit device like a resistor or a light bulb They lose energy due to collisions with atoms in the wire So if we have a current moving to the right in this piece of wire And they're at a higher voltage which means because voltage is energy per Coulomb each charge has more energy When they go through a resistor we transform some of that energy they collide with other molecules This resistor is made up of something so that the positive charges I know the positives don't move but we're gonna pretend that they do from now on so the positive charges Give up their energy and they give it up in the form of heat and then they end up at a lower voltage This energy lost by the charges is transformed into heat and the energy lost by the charges is related to voltage drop Because potential energy is QB that's on your last unit, which is a nice review of the what some of the things you're gonna see on your test Says fill in the steps below to find an expression for the real rate at which the charges lose energy and Check the units so power Which is the rate at which work is done or in this case the rate at which the charges lose energy Power is how much watts this particular electric device requires Power we defined as energy loss or work over time Remember that from unit three So that means power is going to be Q V Over time So far so good And then it says grouping we're gonna write this as Q over T V I'm just gonna say hey, what is Q over T and what is Coulombs per second you remember from lesson one what we called that current current Current as it turns out this is current Power is gonna end up being IV or VI this is called Jules law named after a scientist whose last name was Power equals IV or VI. This is the third and I Think second-last formula on your formula sheet. I think under circuitry atom. It does have current equals Q over T is that right Yes, and then it has vehicles I times R. I know it has that one and then it has Jules law Which one does it have power equals VI? Okay? However, there's actually three different versions of Jules law because remember we also said this We had Ohm's law V equals I times R. Did I say not to then write it down? What's V the same as Jacob? No, what so if I put an IR right there I'll get II another expression for Jules law is I squared R if you plug the voltage law into there That's not on your formula sheet, but in some ways that one I use more often than the other one Or I could get the I by itself. How would I get the I by itself over here? So if I plug for the IV over R I'll get V squared over R These are the three different versions of Jules law that you can get from this first one B It wants the units Well, do you remember what we measure power in? What? What what what yeah, what? Has a whole bunch of made it to everybody Get the whole bunch of you send it back this way That's it down keep it going figure it out So power is the energy drop per Coulomb of charge times the Coulomb's of charge per second Power equals the energy drop per Coulomb of charge that was Jules per Coulomb Times the Coulomb of charge per second and you end up with Jules per second which is So when you have an electronic device and it has the wattage on the side of the electronic device It's saying that's how much power that the charges are going to lose when they go through that device We don't think of it that way what we think of is that's how much power this device is consuming So we think of wattage is positive on the device. It's actually a loss of power going through the resistor. Yep So the rate at which electrical energy is transformed to heat energy is given by power equals Vi But please remember oh I Forgot that I had this as an example It says use ohm's law equals i times r to find two more relations for the power dissipation in a resistor So we said one was i squared r That's if you plug in the i r right there and the other one was V squared over r. I rarely use this one. I Usually use this one. I sometimes use this one All right, all right, let's go technical here in finding the energy lost by the charges technically We should use the work energy theorem which this author writes this way However the charges flow at a constant speed so your change in kinetic is zero You know what for what it's worth getting technical all he's saying is this does work the fact that we can go energy losses Qb we don't need to take the kinetic into account because the charges flow at the same speed throughout the current they don't change their speed So blah blah blah blah blah here's the more interesting questions, so you have a 1400 watt hair dryer And you plug it into a hundred and twenty volt alternating current socket How much current do your house wires have to have? They have a hundred and twenty volts We agree with that. How much current well? I know 1400 watts. What do I measure in watts? Power so I have the power 1400 I Know the voltage is 120 I'd like to find the current have I got an equation that has those things in it. Yep Power equals Vi so I is going to be the power divided by the voltage It's going to be 1400 divided by 120 how many amps of current Taylor. Oh I thought I thought I heard it 11.7 at three six things right 11.7 Easily enough to kill you we said the other day that the death current which would cause your heart to frivolate is 10 to the negative three Amps so this would actually not just cause your heart to palpitate It would probably cause internal burning as well Again, we want to try and give you a gut instinct as to what's a big answer? What's a small answer? It says mix and match the following appliances with their power ratings remember we said power is the rate at which Electrical energy is transformed to heat so what you want to really think about when you're looking at these is which ones move or create the Most heat which ones move or create the least amount of heat so Let's Look here, which of these do you think generates the smallest amount of heat I? Think the clock is going to be zero point one watts, which is my smallest answer over here I'm also going to assume that all of you have put in a light bulb at least once in your life What's the average wattage on a light bulb? Yeah, sixty hundred forty depending on the lighting, but here I see sixty watts I'm going to say that's a light bulb So I'm kind of going process of elimination here With what's remaining? What moves the most heat? Now Brandon said microwave have any of you looked or at the wattage on your microwave or have any of you Cooked microwave food because in the recipe it will say Assuming a blub blank blank blank wattage for your microwave. What are most microwaves around ish? There are around a thousand if I was going to guess Microwave here. I would probably pick the 1200 because it does say large microwave Microwave is about 1200 watts What did you guys say move the most heat? I'm torn right now between the hot water heater and the clothes dryer Okay Well, here's what I'm going to ask which one moves the most heat quicker And I think the clothes dryer does because I think a hot water heater Actually just kind of gradually heats up the water doesn't make it very very hot very very fast So I probably take either answer, but I think a clothes dryer has That many watts and the reason I'm also leaning towards the clothes dryer if any of you look behind your dryer Is it a normal plug? No, you need special plugs for two appliances in your house the stove and the clothes dryer There are 220 volt outlet So I'm gonna bank on clothes dryer being the biggest and I'm gonna blank bank on hot water heater being the next biggest Then I have kitchen fan and computer 150 watts 800 watts. I think a computer throws a lot of heat off where a kitchen fan. It's an electric motor It's gonna draw some power. So I'm gonna go with kitchen fan 150 watts And I'm gonna say a computer is about 800 watts as is a small microwave So small like a camper microwave for example probably 800 watt I have seen them on a provincial as a multiple choice question say a Particular power appliance draws 3,000 watts of power Which of the following appliances is most likely that appliance and we'll have you know a light bulb B electric pencil sharpener C clothes iron D hair dryer probably the clothes iron because that thing gets pretty hot You know so that you do need to have a gut feel for certain Hopefully all of you know a light bulb is 60 to 100 watts and I'm telling you right now a microwave is about a thousand So you got stuff to compare it to you? Electrical energy since power is energy over time or work over time We can solve for energy and find I think energy is gonna be power times time if power is energy loss Divided by time that energy is power times time and that's how we measure your electric builds Anybody know and I know you guys are young you don't pay your own electricity yet But most of you will pay your first utility bill in the next five years or so, you know what they measure your electric bill has Kilowatt hours hear the kilowatt hear the power hours hear the time that's how much energy you use kilowatt hours It's not they're using metric unit because the metric if they used watt seconds in the hideous numbers so kilowatt hours is what they go with okay, so Since a jewel is a regular relatively small unit of electrical energy It's common to use a larger unit the kilowatt hour Power time you can see it right in there one kilowatt hour is 1,000 watts times 3,600 seconds Because 3,600 seconds is one hour So it's 3.6 times 10 to the 6 jewels So a typical household will use 10,000 to 3,000 kilowatt hours of electrical energy per month and you can see if we kept it in jewels You would have let's say a big household 3,000 times 3.6 times 10 to the 6th your bill would be a little Unwealty to read how many jewels of energy that you use so kilowatt hours. It's in the thousands Most of us can do math and keep track of answers in the thousands just for the Environmental nerd within me if a 60 watt light bulb is left on all month 30 days times 24 hours per day How much energy will it use in jewels and in kilowatt hours so in jewels The energy is going to be the power times the time 60 watts of power Times 30 days times 24 hours times 60 minutes times 60 seconds I believe how many jewels of energy if you leave a light bulb on 24 7 for one month of 30 days How many jewels of energy will it use good question? 60 times 30 times 24 times 60 squared I Got that isn't it? Oh, I thought I heard different numbers 1.55 times 10 to the 1 2 3 4 5 6 7 8 is that right? 1.55 times 10 to the 8th jewels How many kilowatt hours is that? Okay Well if one kilowatt hour is that many jewels I think I can go like this 1.55 times 10 to the 8th jewels times one kilowatt hour For every 3.6 times 10 to the 6th jewels I'm using good old physics 11 unit analysis because the jewels cancel So I guess I'm going to take this number on my calculator and divide it by 3.6 times 10 to the 6th And I get 43.2 kilowatt hours, and it's not kilowatt slash hours That would be kilowatts per hour. It's kilowatts is a capital W. I should make that clear, Mr. Dook and the abbreviation for hours I think is lowercase HR So if BC hydro charges six cents per kilowatt hour, how much to leave that bulb on 24 7 for an entire month? times 0.06 six cents Two dollars and sixty cents $2.59 cents if we round off And that's the big problem we have right now here in BC. We get our electricity for cheap So why do we go ballistic about trying to conserve electricity? It's not to save money although it does save you a little bit I mean save a couple bucks and it adds up. It's because there's a limited amount of electricity out there How old are all you 17? So take a guess. Do you think we'll be using more electric devices or fewer electric devices 10 years from now? Yeah, the demand for electricity is going to go up and not just in North America think about all the third world countries that are Gradually moving to second and first world standards of living China being a terrific example. Do you think they're going to want electronic devices? Yeah So it isn't that electricity is so expensive. He's not here in BC. We're blessed with hydroelectric power it is that there's a finite amount and Even the hydroelectric power has environmental damage. We dammed a lot of rivers back in the 40s 50s and 60s How's our salmon fishing doing the past decade or so? Not so great. We didn't think about the possible consequences So what's the moral of the story? You're not shutting the light off to save the money You're shutting the light off to save the planet, which is a different reason, but I think a more important one Okay So shut your lights off don't leave it to be on when you go out Yeah Pit meadows topped BC as a number one power saver during when oh during earth hour when everyone's supposed to turn up lights Okay, I did not know that Send me the link and I'll happily add that to my lesson dead serious Okay, so there's power in a circuit. What's power vi? Oh Yeah, also I squared R and also by the way I use whichever power equation for the stuff that they give me often I'll know the current and the resistor, which is why I use the I squared R one more often Efficiency how much bang for your buck We did efficiency a while ago, but this is also a good review because we're getting towards the end of the year efficiency Was defined as energy or power out to energy or power in Recall that the Greek letter Eta is often used for efficiency. Now. I didn't know that actually I used to just write EFF for efficiency, but you can write that or you can use the Greek letter Eta Which is where our end came from eventually and it's going to be Power out divided by power in Or energy out divided by energy in or work out divided by work in or here's what I really said I don't memorize the equation Evan. I know that if they're asking me to find the efficiency it's always The smaller number divided by the bigger number because if you get an answer bigger than a hundred percent You've either made a mistake or Your name will be more famous than Einstein and Newton because you solve the world's energy problem You'll be on a coin. You'll be on a stamp. You'll be on a bill Assuming you don't own the world yourself by the time all is said and done The reason I say that is I have a specific question in mind. I can't remember what it's on this test Or whether it's in the review, but there's one question where the way that they phrase it When they talk about the power out The word in appears right before that in the sentence And so kids want to put the power out in the bottom because they're used to memorizing the equation and they want to tell me I think it's a light bulb. They want to tell me the light bulb is a hundred and forty percent efficient Be great Ain't gonna happen Okay Now number six is a nice question in That it's a nerdy cool to me It's not so nice in that this really isn't quite what they're gonna ask on the prevention I'm only gonna do parts of this so it says a 60 watt light bulb is connected to a hundred and twenty volts AC Find the current Okay, our equals voltage times current I'm pretty sure that current is gonna be the power divided by the voltage. How many watts of power is this light bulb drawing? 60 divided by household current is 100. Sorry household voltage is 120. I check do some my head 60 over 120 What is that lowest terms? Yeah, this one's gonna dry it draw about half an amp. I Should add the zero two things Still have to kill you More likely you'd get a nasty shock though Probably wouldn't die Wouldn't be pleasant though B What's the resistance of the bulb? Well? V equals I times R R equals V over I How many volts is this bulb hooked up to? 120 how many currents how many amps are flowing through this bulb? 0.5 Careful not 60 you're dividing by 0.5. What's the answer? 240 this is about a 240 What was the symbol for Ohm's do you guys know? My physics teacher called it a mouse hole in a wall Right remember the old cartoons There's your mouse hole in the wall for me. Well, they're not that obvious in real life. Believe me. Oh And the cartoons because they have to make us laugh See what's the efficiency of this bulb? Well efficiency is Gonna be How much you get out divided by how much you get in and it says we're getting 58 watts of light and heat now The problem is Bulbs are actually very inefficient, but it wants us to count the heat as a good thing. So maybe this is a bulb being used to heat stuff Easy bake oven was the classic I was going to say that one or if any of you live on a farm You often have bulbs that in the winter time in chicken coops and things like heat lamps, right? So We're gonna get and then times 100% What's the efficiency of this bulb about 97% efficient Which makes the bulbs sound really really good actually light bulbs the incandescent bulbs are terribly inefficient hence Which is why most office buildings or whatever have the fluorescent bulbs. That was the first big stretch Those are way more efficient because they don't get very hot. They do get still hot after a while Probably in your lifetime LED bulbs will become the standard in fact it was just last year the Phillips light bulb company built an LED bulb That looks just like an incandescent bulb But it uses I think about one one hundredth of the energy. Oh and it's Almost infinite lifetime LED bulbs last decades if you treat them nice The only problem is right now one bulb costs. I think about 30 bucks. They're gonna be gradually coming down in price So probably in your lifetime You'll start to see you you may even see these things go the way of the dodo because the problem with these things is There's mercury on the inside of them. So anytime that one of these breaks technically we have to clear the classroom and I'm gonna break No, but yeah, we have to get like a special there's special procedures to deal with the mercury on the inside the mercury It's mercury inside these So There's a there's a big push right now for those incandescent curvy curly spiral light bulbs I'm I gotta be honest not a big fan of those because of the mercury issue and because In terms of the savings and going green and carbon footprint I think in terms of what it takes to make them the carbon footprint trade-off isn't substantial in terms of bang for your buck Once LED bulbs become around five bucks a piece. I think I'd be willing to make the switch then D how much energy is used? Well, we said that energy was power times time. How many watts? 60 oh You know what? Let's do our energy in kilowatt hours. How many hours of time pass? Oh So this will give us an answer in watt hours, then we'll change it to kilowatt hours. So in watt hours 480 so I think point four eight Killa watt hour because one thousand would be a kilowatt, right? Just about half a kilowatt hour Yeah point zero six times point four eight and you'll get About three cents. I think when all said and done and again, this is the problem Evan It's tough for us because as human beings were naturally lazy and motivated by greed The fact that we're not saving that much money. There are people I don't live my life on all the time It's it's not about saving the cash. It's about recognizing ten years from now fifteen years from now You guys are young. You're part of the technology Generation you understand how much more you're gonna be wanting to use electricity Right Probably most of you still what do any of you still have grandparents that don't use a computer at all It's only a few of you. Oh all my grandparents wouldn't know what to do with a computer My folks got their first one about six years ago because grandchildren can send email. Okay, that's that's a plus My dad has gotten what my dad actually bought himself a printer about a month ago and installed it himself I do plug it in but that was a big step from I was very proud of my dad Okay, he has a laptop now because he's using it for work So so my dad was the was the pre computer generation my high school So I went to junior high in 1983. We had an apple to one apple to in the school My senior high had a full computer lab, but they were way ahead of the game So again Jasmine the moral of the story is you're not turn the light off for money You turn the light off for the future so shut your lights off Save a little bit of energy. It takes very little effort to do some basics How many you're driving? Turn your car off when you're idling Because that actually does with gas prices right now that does add up and in fact I think Who is it GM? I believe GM is coming out with one of their vehicles next year that will Whenever you come to a stop shut itself off and as soon as you give it gas turn itself back on without you having to do a Key thing all you have to do is you have to make sure that you tell the computer controls Where about where the camshaft is when you come to a stop if it stops in the right place Then as soon as you give it gas, it'll just kick on and start going again In rush hour that'd be a huge savings Not just in terms of the greenhouse gases, but I think that would add up So I won't be shocked if in five years that becomes a fairly standard feature for most cars Auto shut off when you come to a stop. Sorry Well car that drives itself I think is gonna be longer term but that that one can be done See the car drives itself is gonna be more expensive and it won't save you money the car that shuts itself off They can probably build the software in for about 500 bucks. I Would think you'd save that within two or three years with today's gas prices the Google cars that drive themselves Turn the page Okay, I'm gonna give you a couple of questions And this is also dealing with power and current some of this ties into last unit anyways, so number one if you know how many watts and you know the voltage you should be able to find the current and The resistance because I gave you three equations for Jules law that has all three of them in there Um, let's cook a hot dog seven nine ten eleven and twelve are all reviewed Unless I see a good electrostatics review question here. No, you guys got a test next class I'm just gonna give you one three and seven for now, and I'm deliberately I Last year I did two lessons today You have a test next class. I'm gonna give you this to study to work on the review But use this please to work on the review tutorial today after school