[John:] Books are are written by ex-examiners and have a spec have several specimen answers. They have here is an answer is too in an exam. This one's excellent because these are the.
[Sarah:] Alright yeah.
[John:] This one erm he sort of tried hard and put a lot in, thinks he should get full marks but he's not going to get very much because he's missed this, he's not answering that properly
[Sarah:] Yeah.
[John:] and he said that. But it's very good to see where people go wrong and to er help you get it right, and that one is the one.... Is it like that in this one?
[Sarah:] What's that? My
[John:] Ah, are showing how people answer different, how they got
[Sarah:] Erm yes er yeah.
[John:] How marks. And right, electricity. Okay what's erm the difference between a metal and a non-metal?
[Sarah:] Erm metal and non-metal. Erm [sigh] a non-metal is... a metal's a solid no?
[John:] Most metals are solid. Erm can you think of a one metal which isn't a solid at normal temperatures?
[Sarah:] No [LAUGHTER].
[John:] Find it you might find it in a thermometer.
[Sarah:] Mercury.
[John:] Right.
[Sarah:] Right.
[John:] So solid non-metals. Some of them are solid some of them aren't. Er physical properties of metals. What will metals do? What can metals do very well that non-metals can't do?
[Sarah:] Erm... well they're hard so they can erm... make things. Because they're
[John:] You can make things. Right
[Sarah:] s
[John:] you can make things with them
[Sarah:] solids.
[John:] Good. They're hard you can make things out of them. Erm a lot of them are shiny. How do you make... erm how do you make wire?
[Sarah:] With metal.
[John:] Okay. How do you make it with the metal? What do you do with the metal to make wire out of it?
[Sarah:] Heat it melt it.
[John:] You don't need to heat it they just there's a bar of it and they pull it. [LAUGHTER]
[Sarah:] Oh right yeah.
[John:] Pull it through a tiny hole. stick it through a dye.
[Sarah:] Mm.
[John:] So it's if you can pull it out it's ductile.
[Sarah:] Mm.
[John:] Have you ever tried hammering any metals?
[Sarah:] No.
[John:] Lead or soft metals you can hammer them into shape. Seen anyone beating a car panel it's got
[Sarah:] Yeah.
[John:] a dent and they're beating it
[Sarah:] Yeah.
[John:] so they're malleable. You can hammer them into shape.
[Sarah:] Right.
[John:] They're ductile malleable don't need the proper words you just say they can be pulled out. If you try that with erm a piece of wood, you try to pull it out into a long thin wire it would just break. Try it
[Sarah:] Yeah.
[John:] with a piece of china or something like that it'll just break.
[Sarah:] Right.
[John:] All metals will stretch out, it'll get thinner ductile. Malleable you can batter it
[Sarah:] Right.
[John:] into shape. So those are the some of the physical properties. Have fairly high melting points. Some of them not as high as the non-metals but most of have got to get to a few hundred degrees C before they start. Erm some of the uses of metals.... Tell me some.
[Sarah:] Oh erm, the uses of metals. What actually what erm oh god
[John:] What could you use metals for?
[Sarah:] Er anything computers
[John:] Right right. So you can use them for because of because of it's cos you can draw it out you can make wires out of it. You can shape it into almost anything. You can make very specially shaped for
[Sarah:] Yeah.
[John:] almost anything. But there's another another use of metals... erm two sticks about say about one's made of wood and one's made of copper. Erm someone's going to heat one end and then hold the other end. Which one would you rather hold?
[Sarah:] Copper.
[John:] Wood.
[Sarah:] Oh!
[John:] We'll try it.
[Sarah:] [LAUGHTER] No the wood one. []
[John:] Why?
[Sarah:] Because wood takes longer to burn, copper would... just you would you could you would feel the heat you had if
[John:] Right.
[Sarah:] you held the the end.
[John:] The wood would be the first to burn but you wouldn't feel much. Wouldn't feel anything
[Sarah:] No.
[John:] holding the end of the wood. But holding the copper after a few seconds the heat all the heat'd be transmitted through
[Sarah:] Yeah.
[John:] to your hands. Conducted it.
[Sarah:] Mm.
[John:] So metals are?
[Sarah:] Conductors.
[John:] Good conductors of?
[Sarah:] [LAUGHTER]
[John:] Go on. Good conductors of what?
[Sarah:] Good conductors of
[John:] Well what's it just been conducting?
[Sarah:] Electricity.
[John:] Good, that's another one. Good conductors of heat.
[Sarah:] Heat yeah.
[John:] And good conductors of electricity.
[Sarah:] Mm.
[John:] Or we sometimes just say, good conductors. So what about the insulators the non-conductors? Can you think of any of those? Materials which are very good at stopping electricity, stopping heat getting through. If if a material conducts electricity well, it conducts heat well because it's very there there there they work on the same process. If it's an insulator it stops heat getting through and it'll stop electricity getting through as well.
[Sarah:] Mm.
[John:] So can you think of any good insulators?
[Sarah:] Erm... erm...
[John:] Oh oh yes.
[Sarah:] Erm
[John:] Erm have you got an ironing board?
[Sarah:] Yeah.
[John:] Got to put the iron down on apart from.
[Sarah:] On plastic.
[John:] So there's a special little bit that you put the iron down on.
[Sarah:] Oh metal.
[John:] Is it metal?
[Sarah:] [LAUGHTER] I dunno []
[John:] Erm sometimes it's asbestos.
[Sarah:] Right.
[John:] Er... the plug and the cable going to any electrical appliance.
[Sarah:] Mm.
[John:] Erm how does it conduct electricity? What's what's insi what's inside that wire that conducts electricity?
[Sarah:] A fuse.
[John:] No, that... what's the wire made of inside?
[Sarah:] Erm no it's not zinc is it? Copper?
[John:] Okay good copper. It's a metal. Inside there's a metal, but it's not just two bare wires is it?
[Sarah:] No.
[John:] So what's wrapped round the bare wires?
[Sarah:] [LAUGHTER] Erm protector so it won't it doesn't erm it slows it down. Does it slow it down? Cos if you had just if you didn't have the thing erm over the wire it would just burn right through very quickly.
[John:] So... is it you've seen you've wired a plug haven't you?
[Sarah:] Yeah.
[John:] Well
[Sarah:] You've always got something covering the wire haven't you?
[John:] Got something covering the wire. What is it?
[Sarah:] Plastic.
[John:] Right. So the plastic is there because it's a good insulator.
[Sarah:] Yeah.
[John:] If you covered the wire with more metal say you put two pieces of wire spare wire
[Sarah:] Mm.
[John:] or wrap some aluminium foil round these to protect them, not going to be much good.
[Sarah:] No.
[John:] Aluminium's a good conductor.
[Sarah:] Yeah.
[John:] Very good conductor. Erm so plastic is an insulator.
[Sarah:] Mm.
[John:] Glass ceramic most of the non-metals are good insulators. Somewhere in be in between are a very interesting group called semiconductors. Have you heard of those?
[Sarah:] I have yeah.
[John:] Yep and they're probably nowadays as more important than the conductors. And that's what we use for electronic circuits. So semiconductors are things that sort of conduct and sort of don't.
[Sarah:] Yeah.
[John:] Erm
[Sarah:] In between.
[John:] they just need a little push to make them go one way or the other so
[Sarah:] Mm.
[John:] because of that we can control, we can say turn on turn off whether they let the electricity go through or not. Erm so semiconductors [cough] Erm tell me about an electrical circuit, how it works.
[Sarah:] Well you have if you're doing an electric circuit you've got to have a er a bulb and a switch.
[John:] Mm.
[Sarah:] And batteries to g to do the circuit and you can have erm volts in it as well.
[John:] Okay what are what are volts?
[Sarah:] Volts erm it's a term used for electricity,
[John:] Okay.
[Sarah:] volts.
[John:] Right, what sort of electricity?
[Sarah:] Currents. The current of the electricity. Good. Doesn't have to be current but it usually is. Best thing to do is to draw a little picture erm... so what does volts measure? The amount of electricity that's going
[John:] Yeah. It measure the the potential, erm... I've got a three volt battery in there, somewhere cos I'm working
[Sarah:] [LAUGHTER]
[John:] I'm going to make you hold one end sort of there's the there's the battery, going to make you put one finger on one terminal the other finger your other hand on the other one.
[Sarah:] Mm.
[John:] One and half volts. Is that going to kill you?
[Sarah:] No.
[John:] No. Erm drive it with erm a hundred and thirty two thousand volts?
[Sarah:] Yes.
[John:] Okay.
[Sarah:] The high voltage
[John:] Why? What's what's the difference then?
[Sarah:] Well it's got a higher voltage.
[John:] Yeah what's what does that mean? Why is that
[Sarah:] It's
[John:] going to be?
[Sarah:] Well it's higher on electricity it'll give me an electric shock.
[John:] Mhm. How does it do it?
[Sarah:] It goes through your nervous system.
[John:] Okay.
[Sarah:] Into you're arteries
[John:] Right
[Sarah:] and your heart.
[John:] Right. So it'll go through you and it'll paralyze your muscles, so you stop breathing and your heart stops.
[Sarah:] Mm.
[John:] And effectively, it's a bit like drowning.
[Sarah:] Mm.
[John:] Erm get your heart started again. So that's another good point erm you know what to do if someone's had an electric shock?
[Sarah:] Don't touch them.
[John:] Right.
[Sarah:] Cos they'll still have electricity
[John:] Okay.
[Sarah:] on them.
[John:] You don't touch them, what do you do?
[Sarah:] Turn off all the mains.
[John:] Good.
[Sarah:] Erm get a stick or something
[John:] Right. Something like a wooden
[Sarah:] Wood.
[John:] stick or
[Sarah:] Yeah.
[John:] a rope rope and loop him round.
[Sarah:] Drag him away from the actual
[John:] Right.
[Sarah:] mains
[John:] Okay. And then what do you do? When you've got them away from the mains, what d'ya do with them?
[Sarah:] Erm god I've done a first [LAUGHTER] aid course. Erm [] what do you do? Right erm. Could you still touch them if you've pulled them away from the mains and everything?
[John:] Yeah. Once you're sure you've pulled them away. But as you say, switch off first and then still use a stick or something to get them away because it maybe the switch doesn't work and maybe that's why they've been electrocuted in the first place. Cos they thought it was switched off
[Sarah:] Yeah.
[John:] and it wasn't. So get them away from the mains and then what do you do?
[Sarah:] Erm do the quick A B C. [LAUGHTER]
[John:] Right, good and erm
[Sarah:] Check the airway, check the breathing, check
[John:] Yeah.
[Sarah:] the circulation.
[John:] And just treat it as a
[Sarah:] Yeah.
[John:] Erm
[Sarah:] Just try and get their heart beat started.
[John:] Get them breathing started because the the longest they've been paralysed er
[Sarah:] Try and get some oxygen in there.
[John:] Get that going and ring for an ambulance.
[Sarah:] Yeah.
[John:] Erm... so what's volts all about? Well it takes a while to explain, but I'll try and do it quickly.... Erm let's see... This is a reservoir of water, right?
[Sarah:] Mm [LAUGHTER]
[John:] Erm if the water's very high and say we have a little a little pipe coming through there in the bottom.
[Sarah:] What's that?
[John:] That's the dam.
[Sarah:] Oh right, yeah. [LAUGHTER]
[John:] So that's the that's the wall and this is the water.
[Sarah:] Right.
[John:] Now if the water's fai water level is fairly low, there'll just be a little trickle coming out here.
[Sarah:] Mm.
[John:] If there's a lot of water in the dam, right up there, just pull the plug out here it's going to really shoot out.
[Sarah:] Yeah.
[John:] Be a lot of pressure there because there's a lot of height
[Sarah:] Mm.
[John:] of water. Well you can think of the height of the water as like a voltage.
[Sarah:] Mm.
[John:] It tells you ho it's called potential volts, measures potential. It measures electrical potential, you can just call it potential. And if you think of what potential it's got erm sort of like this squirt, if you like. If you
[Sarah:] Mm.
[John:] Now if we have a little hole in there, we'll only get a little bit of water coming out, no matter what sort of
[Sarah:] pressure isn't it?
[John:] Well let's say let's say we've got a fixed pressure now, we're not going to mess about with the height of the water, it's a constant hundred feet or so. So if we've got a a tiny hole not much water is going to get out. What does
[Sarah:] No.
[John:] come out will be really sort of squirting out. But not much water will get through. When we had a great big hole in the bottom of the dam,
[Sarah:] More pressure.
[John:] a lot of water would come through. Well that hole is a bit like resistance.
[Sarah:] Yeah.
[John:] Right, so if we've got a lot of volts, so lot of volts, that gives a lot of current. And what's current? Current you can think of as the amount of water that actually gets through, the
[Sarah:] Mm.
[John:] amount of the amount of electricity that actually gets through,
[Sarah:] Mm.
[John:] and the resistance.... If we've got high resistance, what do you think will happen with a high resistance?
[Sarah:] They'll be a lot of current.
[John:] With a high resistance it's resisting the current, it's stopping the current.
[Sarah:] Oh right, yeah.
[John:] Okay, so high resistance gives low current.
[Sarah:] Low current.
[John:] And obviously a low resistance
[Sarah:] Will give a high current.
[John:] gives a high current. A low resistance is a big hole. A high resistance is if there's a tiny little peep hole
[Sarah:] Yeah.
[John:] it was trying to force through that.
[Sarah:] Yeah.
[John:] The current is you can think of it as the amount of water goes through, it's actually the the current is the amount of electrons that get through in a second. So I've got someone here on the outside of the dam counting the electrons as they go past. Well lots through to day, cos there's the big hole or there's a lot of pressure. So if you have a lot of pr a lot of pressure, a lot of a lot of volts
[Sarah:] Mm.
[John:] and a big hole which will give a low resistance, you get a terrific amount
[Sarah:] Yeah.
[John:] going through. If you have a big hole but only tiny little voltage then you won't get much going through. So
[Sarah:] So it's er always the opposite.
[John:] Volts the more volts the more current.
[Sarah:] Yeah.
[John:] But resistance, the more resistance
[Sarah:] Stops it.
[John:] the less you get through.
[Sarah:] Yeah.
[John:] So the current
[Sarah:] reduces
[John:] the current is going to be something like multiplied by the voltage. Right. So if it's got ten times the voltage, you'll get ten ten times the current through. Which is why one and half volts you know won't do you much harm.
[Sarah:] No.
[John:] But assuming your resistance stays the same, your resistance is about one mega million ohms. So if your resistance stays the same and we keep increasing the voltage at some stage you say ooh it feels tingly
[Sarah:] Mm.
[John:] ooh I don't like that. That's around erm sixty seventy volts you can say oh don't like that, ninety volts stop. Erm two forty volts [LAUGHTER]
[Sarah:] [LAUGHTER]
[John:] So current times the voltage and then divide by the resistance, so current equals V over R,
[Sarah:] R.
[John:] you've seen that before.
[Sarah:] Yeah.
[John:] You don't usually write C for current because it gets confused with lots of other like capacitance. So we use I. Erm
[Sarah:] Yeah.
[John:] that's but that's basically how electricity works. And it needs to have a path to get there and back. So you have a battery... and two terminals on it.... Then you have say this goes round to a light bulb... amps
[Sarah:] Mm.
[John:] Doesn't light up. The electric you say oh the electricity can go round there and if it gets light,
[Sarah:] No it's not it's not connecting.
[John:] but can't flow through it and get back. So it's not quite the same as this water analogy cos it's got to have somewhere to go all the way round.
[Sarah:] Yeah.
[John:] Which is why we call it a circuit.... Okay? Erm so if you can try to think about where is the circuit? Where does it start off from, what what started the battery what pole of the battery. Can it get all the round and back to the it'll work.
[Sarah:] Mm.
[John:] If it can't get all the way round cos someone's pulled this wire out, or opened a switch
[Sarah:] That's a short
[John:] or
[Sarah:] circuit, isn't it?
[John:] It's an open circuit.
[Sarah:] [LAUGHTER] Oh []
[John:] It's an open circuit if there's a bit of a circuit missing.
[Sarah:] Oh right, yeah.
[John:] Circuit is missing. A short circuit is when somebody takes a short cut. Now there's the battery.
[Sarah:] That's fine, yeah.
[John:] Right, there's the battery and electricity's got to go we usually talk of positive current going round this way.... Goes along here and through that big resistance, it's a high resistance.... Right? So it's a little a little tiny hole it's trying to get through here.
[Sarah:] Mm.
[John:] And it's stopping it. Not much electricity's getting back. You've got a big thick piece of wire across there, join it up. You're not going to get much current down there at all.
[Sarah:] No.
[John:] Most of it's going to take the easy way short cut because this sort of looks like, something about this big. That sort of pipe.
[Sarah:] Yeah.
[John:] So for the the water to go down the current to flow through.
[Sarah:] Mm.
[John:] So it'll take the short cut, the easy way, making a short circuit. Won't go the long way round, a short circuit.
[Sarah:] No.
[John:] Erm and if did that with a car battery, erm it'll probably explode. I've seen erm a spanner, metal about that thick, vaporize, on the terminals of a car battery. It's erm when you start a car, have you ever been in a car when someone's started it up in gear and the car moves forward?
[Sarah:] Yeah.
[John:] Well that's just the battery doing that.
[Sarah:] Oh right.
[John:] So it's got enough power stored in that battery to do that. And in a few in a fraction of a second, if you try and if you short it all out, give it a very you know great big wide pipe to rush through, the virtually the whole contents of the electricity of the battery tries to get through that, and a spanner is like that, very
[Sarah:] Mm.
[John:] little resistance goes thorough there, heats the metal very rapidly, melts the metals and then turns the turns the molten metal into vapour
[Sarah:] Mm.
[John:] and explodes. And usually the battery explodes.
[Sarah:] Mm.
[John:] So don't drop lumps of metal over batteries.
[Sarah:] [LAUGHTER]
[John:] Very very dangerous.
[Sarah:] Yeah.
[John:] Okay that's the bit about electricity. Let's see
[Sarah:] Alright.
[John:] where we can pick up some marks. Now tell me what erm... what sort of preparation you did for this.
[Sarah:] Well erm we had books like these, topics that we had to cover.
[John:] Yep.
[Sarah:] And er I told Mum the other day that w in double science we've still got to do one and a half topics. And she couldn't believe it cos like, you know, now we've gotta start down getting some revision,
[John:] Mm.
[Sarah:] we've still gotta do one and a half topics of these books. But erm I looked through the books and erm I wrote down notes and things like that, and I looked through my exercise book. And erm at the end they have er questions at the end of each topic.
[John:] Okay.
[Sarah:] Which helps you. This is all about the solar system and that. And erm I just basically did that.
[John:] When you're revising you said the other night, you cover the answers up and try the question. It's erm really about the only way to do it on problems.
[Sarah:] Yeah.
[John:] Because if you look at a problem, and you read through, have someone to work it out you say yeah yeah yeah yeah yeah, and that's yeah obvious. Erm if you have the just the question, and you've got to work it out, it's not so obvious.
[Sarah:] Mm.
[John:] And it's a good way to check if you know it. Right question number two. Nought. We'll start with that one because because no because no one should get nought on a question I think. Because there's always something even if you kno you think you know something you about it. A bit of common sense will usually give you some answers.
[Sarah:] Mm.
[John:] Like erm people always know a lot more than they think they know. And they don't want to put down what they do know cos they think it's obvious.
[Sarah:] Yeah.
[John:] But put it down, they get some marks....
[Sarah:] We haven't done about about circuits.
[John:] Ah, right.
[Sarah:] See, Mum and I looked a bit up in my book
[John:] Right. [reading] Each lamp is fifteen watt, thirty volts. They arrange them in series and plug them into the mains supply. Draw a diagram [], you didn't.
[Sarah:] No. [LAUGHTER]
[John:] So you didn't get anything for that. [LAUGHTER]
[Sarah:] [LAUGHTER]
[John:] [reading] What is the current through each lamp when they're switched on. Show your working. []... Two forty volt. Now right okay. That's definitely give you one for that. [reading] All fuses can be bought. Which fuse should they put in the plug? []
[Sarah:] I put [LAUGHTER] thirteen [].
[John:] Well,
[Sarah:] Mum said usually it's three.
[John:] Well erm
[Sarah:] Cos there's a lot of bulbs to light up, so I thought thirteen.
[John:] Looks
[Sarah:] Give it a higher
[John:] It does it doesn't really matter erm there's only [reading] Give reasons for this choice. If stronger [] circuits, another bit of
[Sarah:] [LAUGHTER]
[John:] Okay erm... Protective device. What's that oh is this the teacher's?
[Sarah:] No I put that in yesterday.
[John:] Later. Right. A fuse is not an insulator okay? It's a conductor.
[Sarah:] [LAUGHTER]
[John:] Right. A fuse again. It's a deliberate weak link. Let's say you're going to tow erm one car with another car. And you've got this good towing rope, you don't want it to snap. You know when towing ropes sometimes
[Sarah:] Mm.
[John:] jerk and they snap. So you have the towing rope and then you have a little bit of old rope that is weaker than your rope.
[Sarah:] Mm.
[John:] And you use that somewhere in the and you tie that to one car and then join that up. So that if something breaks it's going to be that weak old rope, not
[Sarah:] Yeah.
[John:] going to be your new tow rope. Well you can think of it a bit like that. I was tel I was telling you looking at it from another point of view last night of the... What happens when you put electricity through a wire? May I pinch one of your cigarettes? Ooh look at that.
[Sarah:] Yeah. Oh [LAUGHTER] Erm having to put electricity through a wire. Erm it'll either stop the
[John:] Little bit of electricity and then make it more and more
[Sarah:] It will increase the electricity will increase through the wire.
[John:] Right. Okay. So you're increasing the electricity, and what happens to the wire?
[Sarah:] Melt.
[John:] Right. Good. Before it melts I mean no we don't normally melt the wires, what but what happens? You notice the erm you've got an electric fire running, what happens to the flex?
[Sarah:] The flex? What's the flex?
[John:] The flexible connection.
[Sarah:] [LAUGHTER]
[John:] The cable.
[Sarah:] Erm
[John:] The wire that goes to it.
[Sarah:] Well it won't won't work because it'll be
[John:] It's gets
[Sarah:] too hot.
[John:] So whenever electricity whenever electricity goes through a conductor, usually a wire, the wire gets warm.
[Sarah:] Mm.
[John:] Erm the electricity every every bit of wire has got some resistance and erm electricity will be struggling through, warms it up. Er what happens in a light bulb, when you switch on?
[Sarah:] The electricity flows through and lights the bulb up.
[John:] Why does it light up?
[Sarah:] Because electricity's been there's a bit in the bulb that
[John:] How does it how does it make light? How does how does it light?
[Sarah:] The little bulb inside the actual glass bulb.
[John:] Right, something there's something inside the glass bulb and what happens to it?
[Sarah:] Well electricity flows through it.
[John:] Right and what happens when electricity flows through this little coiled coil of wire?
[Sarah:] Lights up. [LAUGHTER]
[John:] Why does it light up?
[Sarah:] [LAUGHTER] I don't know. [] [LAUGHTER]
[John:] I mean the erm your hair dryer doesn't light up when you put electricity through it, does it? Have you ever seen your hair dryer light up?
[Sarah:] [LAUGHTER] No. []
[John:] You have actually I'm sure. Have you ever looked down into the hair dryer?
[Sarah:] Heat.
[John:] Right and you see it red.
[Sarah:] Yeah.
[John:] Especially if it's if as when it first turns on or if the f the fan heater is not blowing very much. And the you see bits of the element glowing red,
[Sarah:] Mm.
[John:] If you if you don't with a hair dryer if you weren't blowing the air over it, what happens? Or say a fan heater erm a fan heater in the bathroom
[Sarah:] Mm.
[John:] It happened to that the other day. Erm as I say it turned the the element on but no fan blowing air over it to cool it
[Sarah:] Did it melt?
[John:] Overheats and it would melt, so because of that they put a little protector thing on to cut out a thermal cut out to stop the current flowing
[Sarah:] Mm.
[John:] or it would just melt. So light bulb, when you turn on it gets warm, then it gets hot, then it gets red hot, then it gets white hot. It gets so hot it's giving off a lot of light erm light bulbs are hot to touch.
[Sarah:] Mm.
[John:] Yes, so they're
[Sarah:] Yeah.
[John:] giving off heat and quite a bit of that heat is coming off as light.
[Sarah:] Right.
[John:] So they're deliberately made so we get light out of them. Erm... that's ohm's law is part of the question, question two. And to work out any of the volt or
[Sarah:] [sneeze]
[John:] Right. Amps amps is current, right?
[Sarah:] Yeah.
[John:] So we'll go back to Ohm's law here. Current is volts divided by resistance. Right current in amps, let's give you two, volts and do you know what we measure resistance in?
[Sarah:] Erm no. I do know but I sh I should know.
[John:] Okay. On her majesty's service. Ohms.
[Sarah:] Ohms! Yeah that's it.
[John:] Called
[Sarah:] Yeah.
[John:] Who's law it was. Now so on that one. Well they give you they even give you fro from that by manipulating then equations you can derive other equations, you come up with other equations. That's one of the equations that you come up with. Okay? So... current is equal to volt is equal to power divided by volt
[Sarah:] Mm.
[John:] Right. erm... Current which one. How many marks next question?
[Sarah:] Three.
[John:] Okay. Erm... There's quite a bit to go into with that but that's hopefully given you some idea of how electricity works.
[Sarah:] Mm.
[John:] The equations they will give you in the book are in that one. Erm they give it er you just have to know what power is. Power is the wattage.
[Sarah:] Mm.
[John:] So erm electric motors are measured in power. Wattage.
[Sarah:] Mm.
[John:] Mopeds. You know when you've got a moped, plate on it?
[Sarah:] Mm.
[John:] And it'll say so many kilowatts.
[Sarah:] Mm. [LAUGHTER]
[John:] It's just a measurement of power.
[Sarah:] Right.
[John:] So instead of measuring horsepower you're measuring kilowatts. Erm okay. Let's have a look at two papers. Right, you've got a lot of twos on that one. Couple of fives on this. Five on number five.... Right again electricity here, you didn't get two marks [reading] Electricity board could use wind generated power in several ways. []... So when there isn't any wind you can use the thermal power stations instead.
[Sarah:] [LAUGHTER] []
[John:] You're something funny by using. Sa saving
[Sarah:] Yeah.
[John:] Erm... I mean I wouldn't necessarily agree with all these markings because everybody who marks the markings are sometimes slightly different.
[Sarah:] Yeah.
[John:] But erm that's a that's a reasonable answer. Two out of three. [reading] What fuels may be used in thermal power stations? []... Two out of three there, so fossil fuels, nuclear reactor, wind and what's the other energy source that you can use? Well not wind.
[Sarah:] Solar.
[John:] Yeah, what fuels need thermal power stations?
[Sarah:] Solar power.
[John:] Erm thermal is the fuel that you're heating. So that's like Erm they use gas power stations as well.
[Sarah:] Yeah.
[John:] So they're probably looking for both fossil fuels which includes gas. Okay, so I think you've got, definitely got the idea there.
[Sarah:] Yeah.
[John:] That's okay.... Now are you alright on charts? Bar charts?
[Sarah:] Yeah, if you turn over I've got eighteen out of twenty two.
[John:] Brilliant. Good that's good. Because that's that's a thing that will apply to all subjects. So if
[Sarah:] Mm.
[John:] you're good at that you can get marks in lots of subjects
[Sarah:] Yeah I'm I'm alright on that.
[John:] just on that. Okay.
[Sarah:] That was all about smoking so [LAUGHTER]... Oh yeah, what's a load in a river? I've got a question
[John:] [spelling] L O A D? []
[Sarah:] Yeah, there.
[John:] Yeah.
[Sarah:] I looked it up but I couldn't
[John:] Erm if you look at a river that's working [LAUGHTER] run running quickly down from the mountains
[Sarah:] Mm.
[John:] to the sea. It's carrying with it a lot of soil, bits of rock,
[Sarah:] Mm.
[John:] that's it's load.
[Sarah:] I put the impact of the river, she didn't
[John:] Mm.
[Sarah:] give me any marks
[John:] No. No. It's it's also called the. It's what it carries down to the
[Sarah:] Mm.
[John:] sea. When it gets to the sea, it slows down. When
[Sarah:] Mm.
[John:] it slows down it drops a lot of the silt, mud and rocks. So higher up it's dropping the rocks.
[Sarah:] Mm.
[John:] As it gets slower and slower it can only carry smaller and smaller particles.
[Sarah:] Mm.
[John:] By the time it gets to the sea then it's slowed down a lot, it's usually carrying very fine silt,
[Sarah:] Mm.
[John:] which it drops as mud. And the mud creeps out further and builds a delta
[Sarah:] Mhm.
[John:] er the Nile delta or the Ganges or the Mississippi delta.
[Sarah:] Yeah.
[John:] Okay so that's what the load is. The
[Sarah:] Right.
[John:] stuff that it's
[Sarah:] The stuff that
[John:] Just the load it's carrying along with.
[Sarah:] Yeah.
[John:] Erm... So you could pick a few up a few marks on that.... Hmm. Yes, good answer. Take it to an expert who'll tell you what's happening. But the question is you have to design the experiment and you have to be the expert.
[Sarah:] [LAUGHTER] Oh yeah. []
[John:] So we get some crops and put a hedge
[Sarah:] [LAUGHTER]
[John:] Well I mean that'll that might be worth a few marks.
[Sarah:] Mm.
[John:] Erm yeah. Don't give it anything to eat. Give it just cereal and see if it eats it. If it doesn't I'm not touching that. hedgehogs are obviously not eating the the wheat and the corn.
[Sarah:] No.
[John:] Should be something else. But
[Sarah:] Mm.
[John:] if it does start eating the wheat, well okay. Now we'll give it a choice of a few other things,
[Sarah:] Mm.
[John:] and see if it eats it when he's not starving. Erm And on to the earth's crust. Iron is one of the most important metals. So of the metals iron is very important, so is copper, because we use it a lot in circuits, erm
[Sarah:] Is that right? [reading] Write in a write a word equation to get [] Is that right?
[John:] Well an equation has an equals sign in it.
[Sarah:] Oh right, yeah.
[John:] So it's one thing plus it's the in this case it's iron plus oxygen gives iron oxide.
[Sarah:] Oh right, okay, yeah.
[John:] Erm so it'll be F E plus O two will give F E two O three
[Sarah:] Yeah.
[John:] erm or F E three O four. There are
[Sarah:] Mm.
[John:] two types of iron oxide. Erm so you just say the symbol. First of all you just think of it in words, the iron plus the oxygen gives iron oxide. If
[Sarah:] Okay.
[John:] you wrote that erm well for one mark, you'd probably wouldn't get
[Sarah:] Probably get
[John:] anything because you want the you they want the equation
[Sarah:] They want the Yeah.
[John:] [reading] what three things can be done to prevent it? [] Erm keep it dry, keep it covered, erm
[Sarah:] I put it
[John:] I wouldn't have given you the mark for covered. Definitely a mark for dry. What do you mean by covered? You usually say erm protected by paint or galvanized.
[Sarah:] Yeah.
[John:] But it needs to be you need to have oxygen and you need water. Keep it away from oxygen is another one. Make sure there's no air around that'll stop it rusting.
[Sarah:] Right.
[John:] Iron ore. Right. iron ore, it comes up every year, erm an alloy. Right. An alloy is when you've got two or more metals mixed together. So
[Sarah:] Right
[John:] erm bronze is copper and tin. an alloy is best when it combines the best of it's component metals. Now we don't we don't need to work with iron. The thick frying pan is cast iron. It's black because it's still got a lot carbon in it. And
[Sarah:] Right.
[John:] it's brittle. If you hit that hard with your hammer, it'll just break.
[Sarah:] Yeah.
[John:] Erm a steel pan, if you hit it with a hammer, it'll dent.
[Sarah:] Mm.
[John:] So stainless steel, is an alloy of iron. Two reasons pure iron to make car exhaust pipes. Right, there's an easy two marks. At least an easy one mark. Why is stainless steel called stainless? Have you seen stainless steel sinks?
[Sarah:] Yeah.
[John:] Okay. Do they rust?
[Sarah:] No.
[John:] So why might it be a good idea to use stainless steel for a car exhaust pipe?
[Sarah:] Because it won't rust then.
[John:] So you won't be replacing your exhaust
[Sarah:] Well yeah.
[John:] every year cos it won't rust away if it's stainless steel. Erm okay, Right. Fancy a [reading] What would you do to produce a movement of the ammeter needle? []... Turn the switch on.... size of the movement more coils put more batteries. [reading] What would you do to reverse the direction of the ammeter needles first movement, B? [] You wouldn't reduce the batteries to reverse it to make it go the other way. You'll reverse the battery. Turn the battery round the other way
[Sarah:] Oh right, yeah.
[John:] in the circuit and then the needle will jump the other way.
[Sarah:] Yeah.
[John:] Three marks here. Electric currents. Induce currents, [reading] transformers work by induced currents, pick out appliances that use for transformer []. Okay a pack is one. Erm a drill,... electric toothbrush probably use a transformer because you want to lower it er an electric shaver would use a transformer. You I think these are what would you run off a transformer. So reading lamp, toothbrush and three marks so we're looking for three of them. Electric
[Sarah:] Yeah.
[John:] shaver you run off and a toothbrush.
[Sarah:] Yeah.
[John:] Erm things you would and you wouldn't want them connected to the mains, stuck in your mouth.
[Sarah:] [LAUGHTER] Yeah. Right.
[John:] So some of them you can work out buy if you know what a transformer does, it steps down all of the current, it reduces the voltage.
[Sarah:] Mm.
[John:] So instead of dealing with sort of high trying to push everything So if you bring your voltage down from two forty volts to say you could get a a transformer, a battery eliminator, for a tape recorder. If you that runs on one and a half volts.
[Sarah:] Mm.
[John:] Three volts sorry, three volts. So plug two forty volts into that, just not
[Sarah:] Mm.
[John:] transformer to bring it down to a lower voltage. So lots of things like that it transforms.
[Sarah:] Right.
[John:] Erm
[Sarah:] That one I that second paper she put the answers in so
[John:] Okay.
[Sarah:] my teacher put the answers in.
[John:] Erm right. [reading] A number of materials including metals are superconductors at very low temperatures. [] They've got very low conducting's the opposite of resistance so the good conductors
[Sarah:] You have a look at the chart. Mum seems to think I was right.
[John:] Right, [reading] What is the crit the critical temperature of superconductor wiring? []
[Sarah:] Oh no, not that one. [LAUGHTER] I've got the wrong one, sorry. []
[John:] So minus a hundred and twenty... there I mean that's they're just the there's not a lot of difference really. Oh no, that's not right. I
[Sarah:] No.
[John:] wouldn't give you any marks for that.
[Sarah:] No.
[John:] Because you didn't put the minus in.
[Sarah:] Yeah.
[John:] That's why.
[Sarah:] There's a chart in here, hang on. No it's in this one. There's a chart and Mum seems to there it is. Read that then and I I put forty two.
[John:] Right. [reading] Four weeks January seventy eight, windmills and electricity demand in California, four weeks of January. [] So that's the electricity demand. And that's the power [reading] What's the highest for Jan seventy eight. [] So the highest forty two.... erm... forty one, forty two
[Sarah:] It doesn't go
[John:] Right forty forty two.... forty two, maybe forty three but it's very close especially that they haven't given any scale
[Sarah:] No.
[John:] to read it. So that's the electricity per so that's fine.
[Sarah:] Yeah, but I got that bit wrong
[John:] Forty two.
[Sarah:] [LAUGHTER]
[John:] Okay well they get they've got lots of them to mark and they marked quickly but I... Looks alright to me that.
[Sarah:] Hmm. Sorry, I just wanted your opinion [LAUGHTER] I mean [].
[John:] Mm. I mean it might be wrong but I can't see
[Sarah:] [LAUGHTER]
[John:] Okay. You don't know much about heptane and ethanols
[Sarah:] Oh no.
[John:] things. Right erm oh it's a bit late to get into organic chemistry
[Sarah:] Yeah.
[John:] so I'll Now are these
[Sarah:] Yeah, her marks were
[John:] Complete complete combustion of ethanol.... Erm... Still haven't got any oxygen. That should be a plus, that's what's wrong with it.
[Sarah:] Mm.
[John:] So should have put a plus there.... Ethanol plus oxygen gives carbon dioxide, water.
[Sarah:] Right.
[John:] Erm so change that. This is your paper isn't it?