hello today we are going to recap electricity so first of all static lectures the static electricity a charged object has static electricity we feel the effects of their static electricity when the charged object becomes discharged so charge can be positive or it can be negative and it comes from electrons electrons are the carriers of charge so if we think about a nucleus a nucleus has electrons orbiting in what we call shells or discrete distance away from the neutron the nucleus and electrons are negative and they're really light so electrons can become free um and those free electrons can move about and carry their negative charge so if we think about uh the where that a metal is set out a metal is a lot of positive ions um being surrounded by some free electrons in a regular loss okay so whenever we rub a polythene rod with a cloth so here's the rod we're going to rub it with this cloth electrons are taken off the cloth and transferred onto the rod so because the rod now gets these electrons moving over it becomes negatively charged the cloth will then also become positively charged because it's lost electrons now the two key tenets of electricity static electricity we've got light charges will repel and opposite charges attract similar to magnets where North and North will repel but North will go to South so whenever we have two leg charges this negative and negative they will repel each other and they will move away so here's a rod suspended on a string if we bring another negative Rod towards this negative Rod the rods has found another string will move away and you can see this this is demonstratable um so that's polythene Rod uh cellulose acetate rod works the other way uh where it loses electrons when rubbed with a cloth and therefore it'll become um positively charged because it is lost electrons so it becomes positively charged and so possibly charged uh whenever we move a positive towards the whenever we move a positive Rod towards the positive charge it will move away uh if one of these was negative it would move closer um sorry I have just copied and pasted that over that's why there's mistakes in that so whenever the negative cellulose acetate Rod comes in close to a positively charged Rod they will be attracted because opposite charges attract and they will move closer together okay so some applications for this we've got electrostatic painting so whenever we have uh the paint particles passing through uh terminal we get the pass through a negative terminal become negatively charged at all the like charges repel so all the paid particles move away from each other and we get a nice even Mist which gives us some nice coating for our electrostatic painting if we then charge the wall and make it positively charged uh the negative in the charged pin particles will be attracted to the positively chargeable and we've got a nice even coat on the wall some digital applications however are lightning so in lightning we can get charges a cloud can become negatively charged where um electrons move towards the bottom of the cloud the air between the Clyde and the negatively charged cloud and the closest thing to give it a path to Earth becomes ionized and it carries the electricity right to the Earth so lightning is a dangerous application of static electricity another dangerous application is if we have a pylon um one of those big electricity poles these wires can become electrically charged with static electricity and if you were to fly a kite um you could hit it and die and get a nasty electric shock from that static electricity okay so current electricity is whenever we have a flow of electric charge and that's what a current is it's a flow of charge okay and electrons or the carriers are charged so we can think about a current as a grip or a bunch of electrons uh flowing around a circuit okay so if you think about this um we'll come we'll come back to the space action current of the circuit we have a lot of electrons in this copper wire okay and the electrons are going to move away from the negative terminal because like charges repel and they're going to move towards the positive terminal because like charges are sorry opposite charges attract okay so that's a group of electrons moving across and that's what charges it's a group of electrons flowing across in the current okay so good conductors are our Metals we discussed earlier that we've got a positive ions and they're surrounded by uh free electrons which are moving through the metal so copper silver steel aluminum all great conductors insulators include wood paper Rubber and cork these don't have free electrons so it's um quite hard to get a good uh a good charge passing through semiconductors are silicon and germanium and they conduct electricity some of the time not all of the time um sometimes something like a diode will conduct electricity only going one way but not going the other way and this um is to do with the energy um one way is less it takes less energy to excite the electrons than it does the other way but that's a bit more advanced than GCSE you just need to know semiconductors are silicon and germanium Okay so we've talked about this and and so what really happens is the electrons move away from the terminal the negative terminal and towards the positive terminal but because they're decided in the 1800s that it was going to be positive to negative and that's the way that electricity flows we still say that that is how electricity flows this is how we talk about electricity is going from positive to negative okay whenever we're talking about circuit diagrams or anything like that okay so some signs I'm just going to really quickly go through these we've got a cell multiple cells made for battery we've got switches a bulb an ammeter a voltmeter ammeter measures current uh my current is measured in amperes or amps and a voltmeter measures voltage which is measured in volts and then we've got a diode which is in a player button just to show the electricity only goes one way we've got a resistor a variable resistor a thermistor and a light dependent resistor um okay so the charge is measured in coulombs which we give the unit c so whenever we talk about charge it'll be like five C current is measured in amperage which we give the unit amps so it'll be like five amps and time of course is equal to seconds so a coulomb of charge is the amount of current that passes over time so one kilo of charge is one amp over one seconds so it'll charge the flow of electrons and you don't need to know this but it's quite interesting it is this many electrons 6.24 times 10 to the 18 electrons and that is how many um electrons are in one coulomb of charge quite important for electricity to know your conversions so one amp is a thousand milliamps melee for millennium but it means a thousand and it's a million microamps so one milliamp is a thousandth of an amp which is and one microamp is a millionth of an amp okay so it's important to know those it's also important to know killer which is um times 10 to the three um probably don't need to know you may need a new Nano which is times 10 to the minus nine uh there are loads of those goes right all the way up either way I'm done as well okay so resistance is just the opposition of a conductor to current so if you think the byte a wire a wire has got lots of atoms and our free electron has to pass through the atoms but it can hit them on the way and these collisions cause resistance to their current so now we increase the temperature we know from kinetic theory that increases the temperature increases the vibrations of the uh of the atoms and therefore there are more collisions so more heat will get more resistance because there's more resistance of the atoms to the electrons okay so here's an experiment where we measure resistance and we get a battery here's the positive terminal here's the um negative terminal and we know what goes from positive to negative so it goes in series three this variable resistor and then branches off in parallel to go through the resistor and then we know the voltage and we'll come to that but volts voltage is constant and power it up so that's why a voltmeter is always connected in parallel and current disconnect is constant in series which is why an ammeter is always constant is always connected in series so this is how we measure the voltage and that's how we measure the amperage or the current so the variable resistor works it's like a coil of wire and it's connected to the positive terminal at one end and the negative terminal is movable along the coil of wire so if we think more about resistance um the longer a wire the more atoms that the electron will have to potentially collide with so a longer wire gives more um resistance when a coil of wire if we are moving that variable resistance along uh we get a longer wire and therefore more resistance a thicker wire and gives um a lower resistance and because there are more electrons that can pass three Etc wire so you'll end up getting lamb less resistance to the thicker The Wire okay so Ohm's law which is expect which is very experimentally verified from this setup shows you that the current nor is proportional to the potential difference across it provided the temperature remains constant so that's also to do with resistance equation for this is the voltage is equal to the current times the resistance resistance is measured in ohms which is given a symbol like that