charge conductors and insulators going to be the topic of this lesson in my new General Physics playlist which when complete will cover a full year of University algebra based physics now this lesson is really an introduction to a new chapter on electric forces and Fields and just like we saw with gravity uh we're going to be able to give a good description for these electric forces and Fields uh and because we have some familiarity with it it's going to make us feel like we understand it uh but make no mistake we're better at giving a description of it than getting a really deep understanding of it just like was the case with gravity my name is Chad and welcome to Chad's prep where my goal is to take the stress out of learning science now if you're new to the channel we've got comprehensive playlists for General chemistry organic chemistry General Physics and high school chemistry and on Chads prep.com you'll find premium Master courses for the same that include study guides and a ton of practice you'll also find comprehensive prep courses for the DAT the MCAT and the oat now it would make a lot of sense if we started this lesson off by first providing a definition for for charge uh but we're going to struggle with that it turns out and just like with gravity uh we're going to be able to provide more of a description of what charges do rather than an actual definition so that's going to be true throughout the whole chapter here so uh turns out uh there are two types of charges and we're going to use an early convention that was adopted long long ago and one's called positive one's called negative and we know that like charges either two positives or two negatives uh repel each other so these two positive charges would feel a repulsive charge away from each other same thing with these two negative charges and then like charges are attracted to each other and again I haven't really supplied a definition of what charge is I've only supplied a description of what charges do so but this is the way it works uh and just like with uh any other property we introduce we're first going to talk about the SI unit and it turns out the SI unit is the Kum abbreviated with a c and kulum was one of the early guys to study uh electric forces and Fields uh and in this case the coolum it turns out is a phenomenal amount of charge it's like uh the amount of charge you might find in like a lightning bolt or something like this and and so typically the problems we're going to deal with are going to deal with much smaller amounts of charge and it's not uncommon to deal with like micrum and nanocs and pums and things of this sort so but the kulum is indeed the SI unit for charge now it turns out there's also a fundamental charge and here's a value you're going to want to know and we symbolize it with the letter e as we'll see here so it's 1.62 * 1019 K so it turns out the nature of charge in matter comes down to protons and electrons protons have a positive charge electrons a negative charge and this is the magnitude of that charge so when you know in a chemistry class we might say that a proton has a plus one charge and an electron has a minus one charge well what we really mean is plus one or minus one of that fundamental charge and so the truth is a proton actually has a charge of POS 1.62 * 1019 K an electron has a charge of 1.62 * 1019 K and any substance that turns out has any sort of positive or negative charge either has an excess of protons or an excess of electrons and that's just the way it works but as a result then that any charge uh any kind of piece of matter has is going to be some multiple of this number if you have let's say two more electrons than protons well in chemistry we might refer to an ion that has two more electrons than protons we might have referred to is having a min-2 charge so but the truth is it's just going to have -2 * 1.62 * 10-9 K of charge uh in this case and again every charge ultimately has to come down to this uh imbalance of protons and electrons and therefore have to be some multiple of this number that's super duper duper important so it could be a multiple of N9 times this or 10 times this but it can't be like 4.7 times this number is the charge on something doesn't work that way this is the most fundament m al unit of charge you can't get smaller than this and every charge on an object has to be some multiple of this number either on the positive side or the negative side you should also know that electrons are much much much lighter somewhere in the ballpark of like you know 1/ 1800th the mass of a proton and so as a result electrons are transferred much more easy than protons also protons are sequestered in the nucleus of an atom whereas electrons are kind of on the outskirts in the electron cloud we might say uh and typically if there's going to be charge being transferred back and forth between objects it's these much lighter electrons that are on the outskirts of atoms that are being transferred not the protons last thing you should know is that charge is conserved so if something changes its charge it's not because charge just vanished off you know out of existence or something like that it's because charge was transferred from one object to another but the overall number of protons and electrons between all the object in play is going to be conserved all right we got a couple other definitions to go with and it's conductor insulator kind of hence the title of this lesson a conductor is any material that allows charge to be kind of move around freely throughout that substance so uh typically we they think of metals as conductors and let's say I've got a metal sphere here and let's say this metal sphere has excess electron so it's going to have an overall negative charge what you'll find out is that these negative charges all repel each other and being a conductor it's going to allow these electrons to move freely throughout the substance and so what are they going to do well they're going to get as far apart as possible and so on the they're going to all move to the outer parts of this sphere so if they were all towards the middle they would be closer together but again they repel each other like charges repel and so as a result of this being a conductor they're going to move and kind of distribute themselves all along the surface of that metal sphere and that's typical of conductors now an insulator on the other hand is going to get a little bit more of a negative definition it's kind of any material that is not a conductor is an insulator uh and typically don't allow the transfer of electrons in the same way and things of the sort as as conduct conductors and definitely don't allow electrons to just kind of move around freely throughout that substance now to kind of Muddy the water here sometimes we also Define what's called a semi conductor and semiconductors are somewhere kind of intermediate between conductors and insulators which makes that negative definition of insulator a little bit problematic because we said anything that's not a conductor is an insulator and then we decided to throw semiconductors into the mix so however semiconductors are somewhat conductive not typically as conductive as say metals and things of this sort uh and it turns out like their temperature depend of their conductivity is going to be different things of this sort uh but things like Silicon uh the the kind of standard for the semiconductor industry um but they're somewhat intermittent between insulators and conductors in their properties including conductivity all right next we want to use the word charging and charging just means uh imparting a charge to an object and typically this is going to happen one of two primary ways and the first we call charging by conduction so and this is when two objects come into contact and because of a difference in charge there's going to be a flow of electrons from from one to the other typically from the more negative to the more positive or you could say the less positive to the more positive but there's going to be a flow of electrons typically if they're in contact long enough until they have the same charge so we'll see this in a question here shortly and then there's going to be charging by induction which is a little more complicated so if we take a look at say uh a sphere here and we're going to take a Charged Rod so in this case we're going to say this Rod has an overall negative charge so an excess of negative charges and I'm going to bring it close to the sphere which is neutral and what's going to happen is it's going to cause the negative charges in the sphere to kind of move to one side leaving a positive charge behind on the other side just due to the repulsion from the negative negatively charged Rod right here but if I move this Rod away so the distribution will move back if as long as this is a conducting sphere and the charges are free to move but what we can do is we can take and connect this sphere to the ground with a wire so and it turns out we'd say that this thing is now grounded so ultimately is connecting it with a conducting wire to the ground uh gives it access to more electrons we like to think of the earth as an infinite reservoir of electrons it can supply electrons as many as you might need or it can receive and suck up electrons as many as you might want to give it it is an infinite reservoir of electrons and so as long as we're grounded here electrons can flow to the Earth or electrons can flow from the earth into the sphere so what we're going to do here uh in this case and in making it grounded is that now in order for these electrons to move away from this negatively charged Rod some of them are actually going to move down towards the Earth and so we're going to lose some of these electrons so in the process just trying to get away from this negatively charged rod and again I still haven't brought these into contact I've just brought them close together and so we can see that this sphere has been induced to have a charge but once again if I move this Rod away these electrons will come back from the earth and it'll go back to being neutral just like it was before so the difference though is what we can do is we can disconnect the wire we're just going to disconnect it while this Rod is still nearby and then we're going to move this Rod away and what we'll see is that because we're no longer connected to the Earth we don't get these electrons back from the Earth from our Reservoir once we move this Rod away and overall we've induced a net positive charge in this lovely sphere now and so and because we've induced it that's why we call this charging by indu uction no contact was ever made between this rod and this sphere so that's why we can't call it conduction so but we've induced it to have a charge only because it was grounded and then uh that grounding was removed once a charge was imparted to it so again had we not remove the grounding wire no net charge would have been imparted uh in the end uh to that lovely sphere so we're going to finish this lesson off with a little bit of practical application and uh example here says if the following two conducting rods are brought into contact for an extended period and then separated what charge will remain on each of them so we got -1 micrum on one positive 16 micrum on the other we going to bring them into contact and that's going to allow uh charges to be transferred so this is charging by conduction they're brought into contact and electrons are going to want to transfer from the more negative to the more positive and I want you to think about why that is exactly well in this case electrons here there's a excess electrons over here that are repelling each other 's excess protons on this side a lack of electrons if you will on this side so the electrons are attracted uh towards the positive 16 microcombs the excess of protons and repelled away from the excess of electrons and this impetus for the electrons to transfer provided they're in contact long enough will continue until there's no more impetus for them to transfer and that's going to ultimately be when they have the same charge and there's no reason for the electrons to want to transfer back and forth at that point all right now we have to remember that charge is conserved and this in this case means not necessarily charge on any one of these two rods but the charge of the system as a whole with -10 micrum and positive 16 microc that's an overall charge of positive 6 micrum and if charge is conserved and these are going to end up with the same charge then we can just split that in half and say that positive3 micrum would be on the rod on the left and positive3 micrum on the rod on the right and it would still add up to a total of positive 6 micrum and charge is conserved so so again this was just pretty much an introductory lesson not a whole lot to it that wasn't uh definitional just a little bit of practical application but in the next lesson we're going to start hitting some math we start dealing with kul's law if you found this lesson helpful consider giving it a like happy studying