[Music] hello prima meticulous i hope you are updated it's pretty particular pre-matriculated okay once more again good afternoon to you all premature killings hope you have been ready to learn more with us as you can see john is up and ready i cannot say anything john how's you i'm really good thank you great to see you again great elevens now last night i just did a little bit of a thing with some of the people watching maths but today i've got the whole show so we're going to do the whole thing so let's get going right talking about what are we doing today what what what it's electro magnetism so it's the connection between electricity and magnetism now you might have played with some magnets we all know about electricity the lights and what have you now we're going to see how they work together how we can put those two ideas of electricity and magnetism together isn't that cool it's so cool you know what two words to describe the show it's just fun and learn absolutely i'm looking forward well mindset is to join us on this fine and landing show make sure that you go over facebook our facebook page is facebook.com forward slash learn extra secondly follow us on twitter at learn extra and lastly you can download the notes they already posted on our facebook page all for free on learn extra dirty or dirty live and let's learn have fun also abram thank you so much right now guys let's get going so electromagnetism so what are we going to do today there are a couple of things we're going to look at the first thing that we're going to look at is we're going to discuss the magnetic effect so let's just get the pen right the magnetic effect of an electric current so we're going to look at how what happens when current passes through a current carrying conductor and we'll be surprised we shouldn't be surprised because you've seen it before that there's a way of if you allow current to pass through a current carrying conductor it produces a magnetic field but then the exciting bit is that we're going to go the other way so we're not only going to say well if a current produces a magnetic field we're going to say what can we do with a magnetic field to produce a current and that's revolutionary it actually transformed the whole of uh human history we would not be in the position where we are today if it wasn't for this understanding that you can take a magnetic field and you can make current from it because if we were just dependent on batteries we'd have a whole lot of lemons and metal stuck into them and have cells like that we wouldn't have all the electrical appliances that we've got we wouldn't have dynamos and motors and generators and i know the grade 12s are going to be learning about that a little later as well so guys this is important this is foundational stuff you need to appreciate and understand that you can both produce a magnetic field from a current but you can use a magnetic field to make a current to make a potential difference and we talk about that as electromagnetic induction and the amazing man that discovered all about this process is called faraday michael faraday he's one of my heroes aubry did you know that michael faraday although he lived a long time ago has got so many things that we can t that we can learn from him he he didn't have a formal education so he was basically kicked out of the house because his mom and dad couldn't look after him at the age of 11 between nine and 11 okay and he had to start working so he was an unemployed youth okay and uh he went and he got a job as a book binder at that stage he hadn't been to school wow he taught himself to read and write wow very interesting okay so so here's a guy that came from absolute poverty if i'm going to ask yeah is there foreign named after him might be might be he's very famous guy and his his fame has spread all over the world so michael faraday comes from a poor background he couldn't read or write even up to the age of 11 or 12 didn't go to school taught himself to read or write became a lab assistant in and at that in those years okay 1780 1790 somewhere around there what happened is that only the people that were from royalty could go to university only they could be scientists the nobility so if you weren't born into noble uh you couldn't study science and you know what the other interesting about michael faraday is he popularized uh science he started to explain principles of science to to ordinary people isn't that amazing so amazing so so i mean he's got lots of inspiration guys i'd like you to do something just as a as a fun exercise see if you can find out about michael faraday and perhaps even post them on the page um i need to okay let's yeah he's an inspiring man he he he's actually got so many things that he found out and he invented and we can just be grateful to michael faraday for for not keeping all his knowledge to himself but by sharing it and making us excited about science but we're saying to the mind sitters they should read yeah read find out about it and you know what he never gave up even though he came he didn't let his background be an excuse for uh determining where he would get to and he actually became a very famous scientist just because he was determined and so the same applies to you you don't think that because you were born in in a poor background from poor family you don't go to a good school that you can't achieve you can achieve if you stick at it so that's my inspirational bit for today let's get on with the science i'm pumped up already okay right guys now let's get going so what's this thing called the magnetic field now i'm going to take you back to some stuff that i'm sure you've done in primary school do you remember when you dealt with magnets so i'm just going to extend this page a little bit and i'm going to just do a little drawing here and and hopefully we can we can get something colored in it so there we go we've got a little block over here and we're going to say let's make that side of the north and let's make that side the south and we've got a little magnet a bar magnet now what do we know happens around a bar magnet well in the space around the bar magnet if i bring anything that is magnetic into that space around here it will be influenced by the bar magnet okay so it will be either retracted or it will be repelled depends on its magnetic properties ever bring another magnet and one of the examples that we use when we do this sort of thing is we take a little compass needle a little compass needle has a a a magnet stuck on a pin and it's able to move so it's free moving okay and what we're going to say is that the north pole of that free moving little compass needle gets repelled by the north pole of the magnet there and so we could move this little plotting compass around the area the region in space and it would form little lines and these little lines that i've drawn here are the beginnings of what we call a magnetic field so it's actually a region in space which will be influenced by anything magnetic one of the things that i'm drawing here is just to show you that these field lines that we draw never cross they always stay next to each other they stay parallel to each other and another important principle and i'm just sketching them here so please don't get me wrong is where there are lots of them so i'm going to just use the green thing green box here notice there are lots of lines cutting through that green box we say this is a pole this is a north pole and we recognize a pole is a region where there is a strong magnetic field this is very strong strong field okay where is where they're further apart from each other so over here where we've got this sort of situation here you'll notice that there are only a few lines cutting through there it's only two one dotted and one one full this is a weak magnetic field because the field lines weak field okay just remember that this is a region in space and even though i've drawn it on the flat board what you need to understand is it's actually also coming out of the board if this was a real magnet a magnet would be in three dimensions so it would be out of the board this way it would be on top of the board and it would be behind the board as well all around it there's this region in space which influences other things that are magnetic a little compass needle iron filings things that have magnetic properties will be influenced either attracted or moved in some way or repelled by the magnetic field okay you got that let's just check that i've covered all those points that are in your notes and i want to just make sure that we understand it so let's go through them quickly magnetic field is the area in which a magnetic object experiences a magnetic force i said repulsion or attraction the correct another word for repulsion attraction is a magnetic force now remember that when we talking about a repulsion and attraction we know that unlike poles will attract each other so a north pole will attract a south pole but a north pole will repel a north pole and a south pole will repel a south pole so like poles will repel each other unlike poles will attract each other you need to know that now that's all about magnets now what about this thing about current now when we've got a moving charge inside a car a conductor okay then we've got a current moving passing through a conductor it creates a magnetic field so moving charge inside a conductor the charge flows down the conductor it creates a magnetic field that's amazing and this was discovered by a man called urstead he was a norwegian some scandinavian guy i think they first discovered either oslo or stockholm can't just remember it off the top of my head right now but urstead had this little contraption and he had a little compass needle almost by accident you know and he turned on a circuit and he noticed the the compass needle just deflected thought hey why is this happening i've got a little compass needle here little conductor and it's moving it's just deflecting what could be causing it that's the curiosity of science that's the amazing thing he didn't just stop there and ignore it he thought hmm what must be happening here and so he began to do some more testing then she discovered that around every current con carrying conductor there is a magnetic field the direction of the magnetic field is defined as the direction in the north pole of a compass rule will change now let's just go to a diagram to try and show this so here i've got a current carrying conductor i hope you can see it it's this one here so i don't want to change that color because it's too much like the magnetic fields that have been drawn so if we pretend that's the current carrying conductor there there's the conductor there's my conductor now what did earth state find he found pretend for a minute my pen is like a current carrying conductor it's not because not in a closed circuit what he said is around it in a circle region around it like that like my close of my fingers there is a magnetic field and so just like he's showing it there in those or we're showing it there in these diagrams as concentric circles at different points along the the length of the conductor it's not just at the end it's not just at the middle it's down the hole of the conductor there is a magnetic field now you've got to get this right you've got to be able to recognize it so if i draw it like this then i understand all the way down there's a concur current carrying conductor notice that it is at 90 degrees or perpendicular to the current so the red arrow here indicates and i'm not going to use red i'm just going to use pink to go over it that is at 90 degrees to the field so if the current is going down that way down the pin the magnetic field's at 90 degrees like that can you see that like that it's at 90 degrees all the way down in a series of these magnetic fields now what you'll notice is that the way they have drawn them here close to the conductor they're close together as they get further apart they do actually get weaker so they get further and further apart so around the magnetic conductor we recognize that they are strongest when they are close to the conductor the direction of the field is given by the compass needle where it points so if we have a conductor we can see the compass needle but there's another way of doing it what we recognize if the current is changed the direction of the current is changed and remember when we're talking about current here we're talking about conventional current from positive to negative so conventional current from positive to negative if it's reversed that means that if we made this one positive now and that one negative the direction of the magnetic field would change as well so guys how are we going to know what that is so i just want to do a quick thing about that just to remember that the magnetic field is continuous it's represented by magnetic fields lines and notice it's three dimensions and we've said that already so how do we work it out i want to just draw it because i love looking at things and drawing them okay so very quickly if we've got a magnetic conductor a current carrying conductor now my drawing to get this thing with 90 degrees ah a battle i really do battle so you know what i'm going to do i'm going to take an end view i'm not going to take a top a sideways view as i've got here i'm going to say what does it look like if i was looking at the current carrying conductor from the end is that fair enough so here's the challenge guys if i to take the si not the side view i take the end view and we'll just write it down here very quickly i know we're almost out of time but i want to just draw this one thing and i'm going to say there's my conductor now what i need you to understand is i'm going to do another one of those i want a second current carrying conductor so i'm going to put it over here like this now when we're dealing with this section of physics what we need to do is have a symbol to represent when things go into the board and out of the board so into the board what shall we do well what they've decided is we'll make that a cross so we'll make that a cross and coming out of the board we'll make it a dot it's a bit like throwing a dot i don't know if you've thrown darts to a board or shot arrows with a bone arrow there's a fin at the back that's it going in the back of the thing the point hey the dot is coming towards me hey i'm a swatch out so now how do we tell what's the magnetic field here now the easy way to do it is you use your right hand guys the right hand rule what we say is the thumb points in the direction of the current and the curl of your fingers shows the direction of the magnetic field we draw the magnetic field as concentric circles that's one circle and then a bigger circle and then a bigger circle right i want you to take a look at those two pictures and i want you to draw use the right hand rule to draw the magnetic field around them and we'll check them after the break abram thank you so much john you know i'm just watching and learning a lot because i'm enjoying the lesson especially when you speak about that because i'm a former dad's player hey excellent yeah you know what you know what i'm saying yes i get it very well and did you know that there's a famous quote that mr faraday once said he said a secret is compressed in three words work finish and publish excellent i like that like it too okay let's go go for a break right see you after the break mindset is welcome back mindset is now on the page there are some exciting comments that i need to read out to our teacher just before we get you know to the actu to action uh vince driva says long time no see where have you been vincent has it and another one uh it's from new york saying my favorite teacher and my uh my favorite subject and my favorite teacher hello to you mr john cool we'll chat to you on on the page as well sometimes people have to do work in the background i'm one of those i don't always get on but uh i'm always there watching what's going on and i wish you all the best thanks for watching enjoying the show and let's learn more let's go guys have you got the answer hey i'm not worried about the fun and games have you got the answer have you done your sketch remember what i asked you to do during the break if you take a drawing like that remember what that means that's saying that we've got a current carrying conductor and the current is going in which direction abram the darts player current is which in or out hey come on in in which way do you throw the dot did you ah and what do you see when you throw the dot you see the the the the the tech yes yeah so it's going in all right okay i see now okay so did you ever stand on the at the front of the board and let other guys throw at you no no no no you wouldn't do that but if you did what would you see you just see the point so here the current is going out with that so over here it's going in because we see the cross cross means in okay point means out got it now we've got to show the direction of the magnetic field is it clockwise or is it anti-clockwise how are we going to work out remember if you did this experimentally you would have your piece of wire pointing down you'd put a little compass needle around you'd see which direction the compass pointed in but here i've said to you the way we're going to do it is we're going to use the right hand rule not the left hand the right hand rule we're going to point the direction of the current with our thumb and we're going to use the curl of our fingers to show the direction of the magnetic field but let me get some field lines out so i've changed the color of this circle here and we try and get it as circular as we can let me just move that one a little bit so it's more or less circular forgive me if it's not totally circular we're just going to draw another one and i'll draw one more as well but let's just get that one as big as we can oh this one i'm going to delete sorry guys because i don't want to have too many we're going to take that one make it big come on there we go now you can see concentric circles they're all they all should be circular this one is playing up this there we go almost a circle but i think that's pretty good okay so it's almost we would draw them with a compass and we draw them nice and circular just making them bigger and bigger and bigger but for a sketch that isn't too bad now what we've got to do is we've got to indicate the direction the direction of the current is given by the right hand rule so in this case i'm going to put the thumb pointing in notice my thumb is in that direction it's going in and i turn my fingers in this direction it's right hand check i know that i write with my left hand so it must be the other hand that i must use so my thumb goes in and the curl of my fingers tells me that this is in a clockwise direction it's in that direction and i can put the arrows on those circles to show that if i put a compass needle this is the important thing if i put a little compass at this point over here the north would be indicated in that direction north would be pointing in that direction and that's why we show the arrows the arrows indicate the direction of the north pole okay so be aware of that now if that was the field direction going in look what's going to happen i'm going to turn around it's now the current is coming out and i'm using my right hand the thumb is now pointing towards you the curl of my fingers is the other way around and i'm just going to quickly put some lines in over here and in fact i'm just going to do one so that we don't waste too much time and indicate that magnetic field as coming in the which direction anti-clockwise direction so guys this is anti-clockwise it's coming around like that now you need to know the right-hand rule you need to be able to use it this is the right hand rule for a straight current carrying conductor okay remember what we said there are many field lines there's one current so the thumb is the one thing it's the current the many fingers are the field lines it's the curl of the fingers got it right let's move on now the next slide just simply indicates that so we're going to skip that on it's in your notes so that you've got it there's no confusion in fact there's one other thing i want to do just quickly let me go back because there's one little thing that i want to prepare you for guys listen to this very carefully if you want to see the pretty pictures you need to go to the mindset lesson on the website i'm going to tell abram what that lesson is and go and have a look at it see if you can watch it online or you can order the dvd it's on electromagnetism in the on the main website under a classroom resources go and have a look at it it shows these beautifully i'm just going to try and sketch them remember what i said to you this picture was the top view what i'd like to say is what happens if i look at it as a side view what would it look like if i looked at it from a side view so i'm just going to draw in one direction now so i'm going to say there's my current carrying conductor and i'm going to say let's pretend the current is in that direction abram help me out heaven yes what did we say how are we going to determine the direction of the magnetic field what do we use what hand do we use right hand and what direction does the thumb pointed uh current it's current yeah and so with if that's the current i'm just going to remind you that that's i so the current is going up okay so now i put my thumb over there current going up what do you notice about the curl of my fingers now it's a bit funny now you're a graphics artist yes okay you're a darts player a graphics artist a radio presenter all sorts of things hey this man's man of many talents eh so you've got to recognize some talent with now abram i'm not a 3d drawer i don't know if you battle with 3d sometimes i don't know you manage it fine but you know what normal people the scientists are right we want to draw it quickly so we don't have time to give it to abram to draw all the time okay so we want to draw those rings okay but hey it's tough man i can't draw in 3d so we got a symbol now the darts play tell me something abram what did we say about our definition for something that is coming out what was that uh something that is coming up coming towards you what's the dart going to look like uh it's a dot or a cross well it's a dot it's a dot yes so guys i want you to imagine that's the the the side view and we're going to take a slice around all those rings now remember they can be going clockwise or anti-clockwise in this case if i was to look from the top i'm recognizing they're going anti-clockwise so they're going like this so they're coming out on the side and going in on that side so out on this side so art means what dot or cross a dot so i'm going to put some dots over here guys now notice something there's a dot there's a dot there's a dot so all the way around the whole length of the of the conductor there are dots saying the magnetic field is coming in which direction out okay on this side magnetic field is going in you got it now the thing that i want to stress here is notice that these magnetic field lines are close to each other because they're close to the conductor they're many as i get further apart further away i won't have so many magnetic fields and so somewhere out here i might only have just a single little magnetic field because it's tapering off the further i get away this weaker the magnetic field remember when they're close lots together strong far away weaker weaker weaker now you know this if you take a magnet you can't stand 20 meters away get get pulled by the magnetic field no not even if you're iron man clunk no no that doesn't happen in real life but if you close just very strong magnets and you've got a piece of metal it will will jump so recognize the magnetic field spreads out over an area this magnetic field is cutting perpendicular to the movement of current now guys this principle is going to be very important when we get to faraday's law so i want you to remember this picture you can go and draw it the other way when the current's the other way but all that we'll find is their dots their crosses on that side and their dots on the side so let's move on i'm going to skip forward and i'm going to say right now very important idea scientists didn't just like to have long straight conductors they turned them into a coil and when you turn a conductor into a coil you get what we call a coil circular coil not difficult to see that but it's also called a solenoid okay when we do this we can find that we got an electromagnet i'm sure even in primary school you might have done this taken some copper wire wound it around a couple of nails connected to a battery used the nails to pick up other things you've made in electromagnets you turn off the battery to open the switch it's no longer a permanent magnet so we can use this idea of a circular coil to create a magnetic a a a temporary magnet an electro magnet remember the word is electromagnetism so this is the first aspect we're taking current and making a magnetic field this is very useful you know what you have electromagnets all around the place you have electromagnets in your large speakers in your in your computers you have electromagnets that are writing on your disks uh you have electromagnets that are putting up switches so electromagnets are really useful and they're very important so we must remember them so what do we recognize there is something very special about the electromagnet if you've got lots of coils you make a stronger electromagnet now there is another right hand rule now i hope you can see the direction of the current is indicated by those arrows so this is rotating in that direction and what we're going to say normally in a this is just a single coil but normally we would have lots of coils together lots of wrappings of wire around we making a magnet an electromagnet the right hand solenoid rule works here now because you've got lots of coils we're now going to say let's use the many fingers many coils to show the direction of the north pole because this coil arrangement the solenoid becomes a replacement for that permanent magnet with the north and south end so look what happens we take the many fingers and we curl them and the thumb is now pointing away can you see right hand my thumb is pointing away from you curl of the fingers that direction the thumb is pointing away that means that this end of the coil is south the other end if i looked on the other side of the board and i went around the back there and i looked at it that end of the magnet would be the north side of the magnet okay the magnetic field around a coil is just like the one we drew of a permanent magnet right let's move on next page and that's what we've shown there so that when a current is passed through a solenoid many coils an electromagnet the electromagnet is just like the bar magnet moving on there are three things that you can do to strengthen an electromagnet you can increase the number of coils you can increase the current and you can replace the metal inside and if you make it a soft iron core and make it bigger then you've got more magnetic field lines passing through that the little uh domains inside the soft iron will line up and they'll become magnetic temporally so those are the three things of increasing the strength of the magnetic field around the solenoid please make sure you learn that it's a question that is often asked in the exams abram are there any questions um so far the mindsetters have asked have answered the question there's a question that was saying is it necessary to use the right hand rule instead of knowing incoming current the current will flow in clockwise direction and outcoming current goes anticlockwise direction look you can learn it like that i just like to have a hand rule a memory thing because in the exam you know what i could just forget it but i know the right-hand rule and i know that that always works and i'm not going to get confused it just helps me with my deciding okay so it's more for you not to make some mistakes yeah make not make sure it's recognized as a rule that we use in determining the current okay all right yes we're about to take a break here's a quote from mr faraday from your mindsets about the household massage says there is no more open door by which you can enter into the study of natural philosophy than by considering the physical phenomena uh phenomena of a candle i like that one thank you so much mafana and do not move mindsets see you after the break welcome back mindset is now exciting news that i need to tell you from the 25th to the 27th on saturday we'll be having a future ed an education show happening at coca-cola dome in jonas back so make sure that you do come through whether it's thursday or friday or saturday to meet us as your presenters and also to help uh you understand more about mindset so join let's take it away thanks abraham guys futurehead don't miss it if you're in karting be there don't miss it you can register for free yeah it's free you can get in there lots of giveaways there are competitions hey we're running a really cool one so make sure you there put your name in the box there's a lucky draw every day at three o'clock make sure you get in and you could be a really lucky winner there's lots of stuff that's happening at future ed i'll be there on saturday so hope i'll see you right guys let's get going here we go the first part and i know we ran over a little bit of time the last two sections we've been dealing with current produces magnetic field and we've set some things up okay talked about what a magnetic field is now we're going to go the other way and this was the debate that lots of people had you know what they they thought it was going to happen but they couldn't quite get it right they thought if they got a big enough magnet it would produce a current hey they got big magnets they made big electromagnets and they tried to measure current around them and there was nothing they turned the wires this way they turned the wires that way they made coils around nothing happened and then michael faraday one day he was setting up part of the equipment and he suddenly just moved one of the coils huh there the needle deflected and so what he found out was just like you need a moving charge to create a magnetic field you need a moving magnetic field to create a current to make the charge move so very important idea there has to be relative motion and this little animation here on the board describes faraday's law quite nicely so what we've got is we've got a coil now notice the potential difference before the magnet moves in is zero the magnet with the north pole moving in and it deflects to one side when it comes out the red needle deflects to the other side so watch this very carefully watch very carefully and i'm just going to highlight where you must watch watch the movement of the coil watch the movement of the magnet and the deflection of the needle as the magnet goes into the coil look there's no battery here there's no battery this is a voltmeter that's centered at zero which we sometimes call a galvanometer a galvan a galvanometer okay galvanometer at least galvanometer and we're showing that it can go positive and it can go negative depending on the direction that that magnet is moving now you could have the magnet stationary and you could move the coil backwards and forwards over on top of it it doesn't mean that the magnet always has to move it's about relative motion and if we move uh so they need to relative motion sorry i didn't spell it they need to move relative to one another the magnet could be fixed and the coil could move around it or the coil can be fixed and the magnet can move in it in and out okay now notice that when the speed of the magnet this is the other thing if the magnet moves faster the quicker it moves in the bigger the deflection and now faraday had to explain this or scientists had to explain it and so what we recognize is by doing some experiments what they recognized is this reading on the voltmeter we called induced it wasn't there to start so it was an induced emf an emf is maximum potential so we call it induced emf okay and what we're saying is the induced emf if there is a closed circuit then there will be an induced current now to change the current you could change the speed of the movement of the magnets relative to the conductor so i've explained that you could also change the magnitude of the change in magnetic flux whoa whoa whoa what change in magnetic flux what is this all about let's try and explain that the last one we'll come back to this one now the number of turns in the solenoid so if we increase the number of turns we get it bigger emf so there's something that we've got here that's change in magnetic flux hey don't get me tied up with big words let me try and explain them to you i just want to to recognize one thing the direction of the induced current can be determined by the right hand rule now we'll come back to that point as well but what's this idea of magnetic flux so magnetic flux i'm just going to draw it over here it's given this fancy symbol phi okay it's a greek letter and it's not pi but it's phi so i know we had pi day a little while ago in in march but we've now got phi phi the magnetic flux is called is given by this it's the perpendicular magnetic field times the area okay it's the strength of the perpendicular the magnetic field perpendicular to an area it's the component perpendicular component of a magnetic field times its area the area through which it passes so let's just be very clear about this so if you remember i said to you earlier on i drew a nice diagram on this diagram here what we've got here is field lines and perpendicular to these field lines we've got an area okay if we keep the area and we change the area we take area by magnetic field the strength of the magnetic field that all those magnetic field lines are perpendicular to that area the field lines represent the b and the border represents the a if we multiply the strength of the magnetic field by the area we get that thing that we're talking about fire magnetic flux now how can we change the magnetic flux well let's just make very sure that we've got this and we've got it very clearly first thing we said the magnitude of the change in magnetic flux so guys here is what faraday found it if we've got magnetic flux just from a magnet there's an area through which those field lines work and what we've got to do is as we move them into the coil they cut across the coil and we only want the ones that are cutting at 90 degrees across the coil if the coil has very few then if they're all the same and they don't then there's no change if we just have a magnet inside the coil no change but if we move it we change the movement then we're changing those magnetic field lines the area that those cut through and intersect with the coil becomes bigger or smaller depending on the motion and so that's the idea that we've got as we move the magnet in and out we're changing the magnetic flux how can we cause the change to to occur well we can use two things we can change the area in other words make a different sized coil we can also use a different magnet bigger magnet all of those things are possible so in your notes it will go through this idea that the magnetic flux is the product of the perpendicular component of the magnetic field b and the area there's the formula and if we looking at perpendicular we use this cos theta as a way of working out the angle between the magnetic field and the area if we've got the angle between them we can work it out i want to move on because i want to define faraday's law so what did faraday say the faraday's law of electromagnetic induction states that when a magnetic field moves relative to a conductor so like a coil an emf is induced in the conductor or across the ends of the conductor guys if that's not a closed circuit there will still be an emf there okay there will be an emf there when there's a closed circuit in the in the coil then current is induced in that circuit very important difference to note what we're saying is the induced emf in the coil is directly proportional to the rate of change of magnetic flux so there's some important things here and we are recording them in the equation this e symbol stands for induced emf okay the n stands for number of turns of coils the phi is b times a times cos theta where theta is the angle between those and delta t stands for the change in time now that's a mean equation but it's not that difficult don't get a panic it's really easy because they will give you most of those readings most of those values okay so don't panic about it read the questions and we'll see if we've got time to do one or two just remember the principle as we moving the magnetic the magnet the field cutting across the coil is changing that area is changing so there's a change in magnetic flux if the magnet isn't moving or the coil isn't moving there's no change there'll be no emf the bigger the magnet the the magnetic flux is the bigger the emf will be the quicker you do it in other words the smaller the time the bigger the answer is going to be the more the number of turns the bigger the answer is going to be last thing i want to just go back to is you can determine it said on the previous page the direction of the current by using the right-hand rule now i want to just show that to you and it's difficult to show it when it's moving but just very carefully here is the rule what we recognize when we put the north pole in when the north goes in so north goes in then this end of the bar magnet will become north as well okay they will want to repel each other as the north moves in the magnetic field around here wants to be a north pole so we would recognize use the right hand rule to say this end the current must be going in this dot well let's just get it the current must be going in that direction because that end would then be north as i pull it out this end must oppose the the action so as you put it in it wants to push it out as you pull it out it wants to pull it back in so this end must then be south and it wants to attract it the current will be in the opposite direction and that's why the needle flicks backwards and forwards now abram are there any questions on the page any people wanting some help uh before i get to our question because i think you know what we've almost run out of time okay for now i think you can just take that question and i'll give you one question from the mindset is okay take one quick one yeah you're gonna give it to me now i'll give you after that okay right so let's make sure that we've got this guys if we want to make the induced emf bigger then what you need to do is it depends on the area covered by the magnet the strength of the magnetic field the rate of change in the number of turns now the questions were quite straightforward and most of them we've actually already answered and i want to just mention that so we've stated the law guys this often comes up in the exam so please learn it don't just forget it don't just depend on the equation and learn it here's the question yeah the question from two mindsets are saying what is the magnetic flux okay i've explained magnetic flux i'll explain it one more time magnetic flux phi is the strength of the magnetic field times the area through which it passes but they've got to be at 90 degrees so we use cos theta for that or we can say it's the perpendicular component passing through an area if you haven't got the idea of magnetic field go back or magnetic flux at least go back and look at that diagram i drew with the magnetic field lines with the crosses and dots and a box around them it's that area okay thanks abraham thank you very much joan it's been a great job really really learned a lot so are the mindsets out of mind sitters at home that's great it's always a pleasure to be here and i'd see you again work hard right thank you very much mindsetters remember you can also still send us your questions on our facebook page or email us at help desk at learn extraterrestrial otherwise it's been a really really great show and i love the spirit of mindsets who are helping one another on their page that's why we like team spirit and see you on thursday or friday or saturday at the career exhibition future at the education show 25th to the 27th coca-cola dome right bye [Music] [Applause] you