Transcript for:
Electricity and Magnetism Lecture

okay okay so in this session we're going to be talking about everybody's favorite unit electricity and magnetism so remember this is split into two parts both electricity and magnetism all right so it's technically two units but it's not as long as full two separate units before we continue remember the syllabus has been changed starting from 2023 onwards and some topics were removed some topics were added when it comes to electricity the topic that was removed from O Level physics was Digital Electronics and that involved digital and analog circuits as well as logic gates so to the students who are studying all level physics core students will not be affected of course students will not be affected if you see things like this for example or this these are what we call logic gates as some of you have studied computer science before have probably seen these these have been removed from the syllabus right however the mention of digital and analog as as Information Systems has not been completely removed it's actually been shifted to waves when it comes to communication and such so we're going to select them later additionally a new unit of energy was added called the kilowatt hour and we're going to study that so it's a very simple thing it's what we use to measure electrical energy consumed at home but that's another story so it comes to electricity these are the topics that have been changed and note to course students of course or pre-ig CSE or year 9 students if you see the term extended on a page know that this is not for you however it's very useful if you watch that section and try to understand it because it'll help round out your understanding of the topic and unlike unit one for example where there was an entire chapter that you didn't need to study here there are just minor rules that have been skipped for your sake but listen to them nonetheless they will definitely help so what are we studying today we're studying electricity and magnetism so we're splitting them up into electricity and magnetism from the electricity point of view we have static electricity so what's a charge positive negative attraction repulsion charging electric Fields basic stuff won't take long but the most important part of electricity would be current electricity so circuits so what is a circuit what's voltage what's current what's resistance what are resistors how do you connect them in series and pattern them what are potential dividers like different types of stuff and we'll finalize electricity by talking about electrical safety features that we have at home like the fused the circuit breaker and Earth wires and why do we need these features next let's talk about magnetism we're going to split them into two major parts although the second major part is split into three the basics of magnetism as in what's a magnet what's a magnetic field and how an electric current can produce a magnetic field so you have electromagnets and coils and their applications and then we have different electromagnetic applications specifically three things the motor the generator and the Transformer so we're going to find three distinct sections when it comes to magnetism and electricity together let's get started with static electricity the word static if anybody doesn't know means not moving so when we're talking about static electricity we mean the electricity is not moving so it's not a circuit per se there's no flowing charges and so on although charges will move but they will mostly move in order to stick from one object to the next and make something either positively or negatively charged So speaking of charge what is charge a charge defined as a property of matter that experiences a force when next to other charges or in an electric field but what do I even mean by that if you take a look at an atom inside an atom there are protons and neutrons and electrons these are the three subatomic particles in an atom a proton is positively charged an electron is negatively charged whereas a neutron is neutral charge is something that all matter has everything has charge everything is either positive or negative and that's because everything is made up of protons and electrons neutrons are charged or neutral I'm sorry even though they should be charged because they have both positive and negative charges inside them so if something is neutral it doesn't mean it literally has no charges it simply means it has both positive and negative charges in equal amounts at the bot they're equal so there's a resultant is zero basic concepts positive and positive repel negative and negative repel positive and negative attract likables or charges repel Opposites Attract but neutral objects are also attracted to charged objects so if something is positive or negative it's also attracted to things that are neutral okay great because they have both positive and negative charges now charge as a quantity has a unit of measurement this unit of measurement is called the coulomb so a proton has a certain amount of charging coulomb certain amount of charging coulombs for the negative and so on good now when it comes to charging objects or like a charge itself it has a region around it called an electric field we'll talk about charging objects after this what's a field it's a region where charges experience a force so for example here I have a positively charged ball if I put a positive charge here it'll get repellent which means it'll experience a force so we show this Force by drawing lines these lines are always drawn coming out of a positively charged object or into a negatively charged object why because the direction of this Arrow of this line of these lines shows me the direction on a positive particle it shows me the direction of the force on a positive particle now you might be thinking what about the negative what will that do if you have a negative charge it'll just move opposite to the direction of the electric field lines because negative and positive attracts would move towards the positive negative and negative repel it'll move away from the nectar now one more feature the space between the lines represents how strong the field is the closer the lines are to each other the stronger the field is and the farther away the lines are from each other the weaker the field is okay good if you put a positively charged object next to a negatively charged object their fields will join together to form a combined field if you have two spheres the field will look like this it will move from positive to negative and the field strength changes being strong here weak here and strong here but if you have two flat plates one is positive one is negative the field lines will move from positive to negative just like usual from positive to negative but because the surfaces are flat the spaces between the field lines are constant they don't change they're equal and if the space is between the field lines are constant or equal they don't change we call this a uniform field the word uniform mean meaning constant so the field strength is also constant good so going back to core stuff for a bit you can charge and insulate it by rubbing it with another insulator so if you have a cloth a cotton cloth for example and a glass rod or a plastic rod and you rub them together the friction between them causes one of the objects to lose electrons and the other gains electrons so by rubbing them the cloth loses electrons and it's gained by the rod for example which means that if you separate them the crowd becomes negatively charged because it has gained electrons whereas the cloth becomes positively charged because it has lost electrons so the only way of charging something is by either having that something lose or gain electrons lose or gain electrons now which one is losing which one is gaining I genuinely don't know it depends on the materials but if the question tells you that hey electrons have moved from one object to the other then that's your clue that's your key whatever gains electrons is negative whatever loses electrons is positive yeah you can also charge a conductor by induction but let me preface this by saying something in the curriculum in the document there is no mention of induction directly but there is a mention of understanding how things are charged when the electrons move so I'm keeping this in here all right so charging a metal by induction is not mentioned in the curriculum document directly as is but a mention of charging a substance by adding or removal of electrons is mentioned so it I'll just keep it as is if you have a metal ball metals are good conductors of electricity why because they have three moving electrons so not only do they have you know most of the negative charges in their atoms they also have free moving negative charges floating around like I said last timer guys remember to hydrate so how do you charge this if you get a positively charged rod for example or let's make it negative I'm feeling negative right now say negative what's going to visually happen in front of your eyes is that this entire ball is going to move towards the negative rod no that's cool and all no problem at all but what's going to happen inside is this this left side becomes positively charged and the right side becomes negatively charged so the distribution of charges changes now the ball is still neutral by the way right now it is still neutral number of positive charges equals number of negative charges but if you connect this ball to what we call an earth wire or a ground wire or just any other conductor these electrons are going to get repelled out of the metal sphere so the metal sphere now becomes look positively charged what we then do is we remove this ground wire if you remove the ground wire there is no way for these electrons to go back so now the sphere is positively charged so here are the steps you bring close and negatively charged Rod or positive doesn't really matter much and then you connect this metal sphere with an earth or a ground wire and then you remove the wire or the conductor before removing the rod this will charge your metal conductor if you want to give the metal ball a positive charge you use a negative rod if you want to give the metal ball a negative charge you use a positive rod it always charges the opposite charge and that's static electricity very short very succinct and honestly not very uh I don't want to say important but it doesn't really show up in a lot of questions current electricity now take a deep breath because I know I do need to take a deep breath we're going to start current electricity this is very important almost all of electricity relies on your understanding the difference between voltage and current and resistance before we start short story if you have a circuit it's the purpose of this circuit the purpose of this circuit lets in front of you right now is to deliver energy from a source of power like this battery to a device that needs the energy like the bulb the way we do this is by connecting this electrical source of energy using metal wires copper wires are the best so that you have a circuit a loop once you close your switch and when I say close the switch I mean the circuit is going to be on if I tell you we open the switch the circuit's going to be up so once you close the switch charges positive charges leave the positive side of the battery and each one of these charges carries with it oops I don't know why to do that carries with it electrical energy so every one of these charges carries with it some energy these charges move move move move and move through the circuit the reason they're moving is because the battery is giving them a push so the battery is responsible for the pushing it's applying a force on them to push the charges through once the charges reach the light bulb the light bulb has a property that we call resistance it tries to slow down the charges so as the charges go through the light bulb they lose their energy something similar to friction and as friction produces heat the friction and friction between the charges and the light bulb itself releases electrical energy into the light bulb so the light bulb lights up these charges then get pushed back or pulled back to the battery they gain some more energy they're pushed out and you have a circuit so the purpose of a circuit is to deliver energy from the battery the source of energy to a device that needs it but we need a full loop a closed loop a circuit all right good next we're not going to be drawing circuits like that though we're often going to use circuit symbols so here are the symbols this is the symbol for a battery this is a symbol for a switch which is a symbol for a light bulb that's all there is to it battery switch light bulb the long line of the battery is the positive charge the Short Line is the negative charge here's a light bulb you want to call us the ladybug lamb the switch is always drawn open I don't care what the orientation of the switch is it's just always drawn open next now let's define our three most important quantities when it comes to electricity voltage which is V current which is I now the reason is called I is because the full term is electric current intensity so they plop the eye from intensity and use that here but we stopped calling it intensely a long time ago we just call it current but the letter I stuck and resistance which is r very good yeah next up what is voltage voltage is defined as how much energy there is per charge how much energy there is per charge and the unit is voltage so for example a battery or a cell that has a voltage of 10 volts means it delivers 10 joules of energy per charge per coulomb like every one of those circles carries 10 with it is calculated using V equals a over Q where V is voltage e is energy and Q is charged now there are two different names for voltage which we call potential difference or EMF electromotive Force potential difference they both mean voltage but potential difference is the voltage across something like the light bulb or a resistor whereas EMF is the voltage of a battery or a cell or a power supply why why are the why is there a difference because this is technically energy lost by the charge whereas electromotive forces the energy gained by the charge on the battery they're both defined as energy per charge but potential difference is the energy lost by each charge is the energy lost by each charge is the energy lost by each charge through a conductor whereas electromotive force is the energy gained by its charge and it's used to drive the charge through the entire circuit so we need that energy to push the charge through the entire a circle very good yeah sorry for a second there I I froze for a bit because I realized I forgot to turn off the annotations and somebody started writing on the on the screen I Know Who You Are by the way I know who you are I'm gonna go and find you wait I should do a Liam Neeson impression wait wait I'm gonna find YouTube okay no I'm sorry have you watched Taken I love that movie Taken is so cool anyway moving on you should watch taken if you have um anyway what's going on current is defined as the rate of flow of charges which is the number of charges that go through the circuit per second it's basically how fast the charges go around the circuit the unit of measurement of current is Empire so basically current is how many amperes or coulombs their charges go through the circuit per unit time per second so if I tell you that a current in a circuit is 2 ampere this means that you have two charges that go through the circuit every second there are two charges that go through the circuit every second speaking of the direction of the charge the current often is from positive to negative this is what we call the conventional current but you will remember you will remember that we said the charges that are free to move inside the circuit are the electrons hmm electrons but what's going on if the electrons actually move from negative to positive so shouldn't the current be from negative to positive we say no we know either made a mistake a very long time ago but we're sticking to the mistake the current will always be from positive to negative but but to recognize the mistake we also say that hey the charges that actually flow in the circuit are the electrons and the electrons flow from negative to positive so if the quest if a question ever asks you to State what type of particle actually moves in the circuit you see electrons all right but if I ask you what's the direction of the current it's from positive connect electrons are related to post now finally resistance that's the thing in the light bulb is a property that resists the flow of charges but why because inside any conducting wire there are atoms and these atoms are vibrating so when a poor electron is trying to go through because the battery is giving it a push it keeps colliding with the atoms in the way causing it to lose energy as it collides with the atoms some materials are very good conductors which means they have a lot of free moving electrons and very low resistance in the atoms are designed or arranged in such a way to allow charges to move freely through them whereas some materials have high resistance they have very few removing electrons and the atoms are not really helping so the basic concept is this the higher the resistance of a material the lower the current so the current decreases and if you decrease the resistance going through of a material the current will increase very good the unit of measurement of resistance is called ohm very good [Music] next how do we measure voltage and current right there are measuring instruments that we use to measure voltage we use what we call a voltmeter and it's always connected in parallel to the component that you want to measure so if I ask you to draw a voltmeter connected to measure the potential difference across the light bulb this is very connected parallel to the light bulb draw a voltmeter to measure the EMF across a battery then you connect it across the battery in order to measure current we use an ammeter which is used to measure current now an ammeter is always placed in series in a circuit and it doesn't matter if we put it here or here as long as it's part of the same wire in the same circuit the current will be the same so let's do it good next the most important equation we have is Ohm's Law which is literally an equation so it's V equals IR or you could just rearrange it and say R equals V over I or you could rearrange it and say I equals V over or rearranging this formula is extremely important we're basically going to use this forever Endeavor endeavor every time we solve electricity so please keep that in mind all right so here's one thing though there's one more thing the resistance of a resistor the resistance of resistor has to what be constant for this equation to work because if the resistor keeps changing the values of the current in the circuit will change the resistance has to be constant sure a certain value of resistance will give you a certain value of current but the resistance still has to be the same and for it to be the same the temperature has to be constant now you may be you might be wondering why because if you go back remember I said resistance exists because atoms and a material cause the electrons to bump into them so they resist right if you heat up a metal object these atoms vibrate faster and as they vibrate faster they Collide harder with these electrons making it even harder for them to go through yeah they keep colliding a lot until they are finally we're through right so temperature has to be constant now let's use this equation before I answer a question that was calculate the potential difference that's voltage needed to drive an 0.02 ampere current so that's current through a 500 Ohm resistor that's R well that's easy I want V so V equals IR I is O Point O2 R is 500. so 0.02 times 500 this gives me 10 volts there's nothing special yeah if anybody has any questions send them now but I'll be answering a question here as well so how will the current be the same if a device has resistance well I'm saying the current will be the same throughout the entire circle so for example if I tell you hey the current is 0.02 the speed of the charges will be a constant 0.02 from the very beginning to the end it won't change it has that value from the beginning because the battery already knows what the resistance is so when it releases a current I equals B over r it already knows what its voltage and resistance are so it gives out the current at that fixed speed from the beginning it doesn't change gives out the current at fixed speed from the beginning with no change what's up if you increase the resistance as in you add another resistor or you change this lamp to one with a higher resistance the current will decrease but it will still be constant throughout the same wire all right the resistance has decreased the current but it does not decrease inside the lamp only no no no no no no it decreases from the very moment it leaves so actually here's the thing a lot of people have this image charge leaves super fast oh my God there's resistance I have to slow down and then once it leaves room super fast no it doesn't do that what happens God that's a silly what happens is this the charge leaves and moves at the very low current that it will be moving with through the land now you might be wondering why why would it do that because if you remember the very first story all of these charges move together they're like a big chain like a train foreign if one of them slows down all of them have to slow down and move at the same speed so it doesn't move fast and then slow and then fast no it just moves at the same speed from the beginning okay how does resistance affect voltage that's the second question for now it does not affect voltage for now resistance does not affect voltage you want to know why because I choose which resistance to put in using the lamp I choose which voltage to put in using the battery they don't affect each other they both however affect the current the poor current gets slapped around by resistance and voltage however this will change in a little bit this will change in a little bit I have a third question which is extremely important where is Mr you I don't know he retired he saw the 2023 syllabus and retired anyway thank God some people remember the OG videos yeah now buyers in general have resistance often connecting wires in a circuit are made of copper so they virtually have no resistance but but the resistance of any wire depends on two things the length of the wire and the cross-sectional area of The Wire again the length of the wire in the cross-sectional area of The Wire what do I mean the longer you make a wire if I have a wire of this length and it has a resistance of 101 if I get a longer wire if I double the length this will have resistance of 20 ohms so resistance is directly proportional to length if you have a wire of this thickness and you double the area you make it thicker same length but thicker the resistance will decrease to 10 ohms which means resistance is inversely proportional to area so if the length increases resistance increases if the area increases resistance decreases I often like to write it down like this R is proportional to L over a so I always remember who's directly proportional and who's inversely proportional now clearly material also has an effect the material use has an effect but it's irrelevant for them [Music] if you remember in unit 1 we defined a very important quantity called power power is defined as energy over time power is defined as energy over time but in electricity we don't measure energy and time we measure voltage and current using a voltmeter and an ammeter so we calculate power using V times I no Fanfare it's just V times I right if I want to calculate energy you go back to unit one energy is Power Times time if you can get energy using V times I then it'll be v i times time I'll replace power with VI let's see how we can use this here's an example an electric fan requires 230 volts and 0.5 ampere to it so Voltron current calculate the power of the fan okay cool power equals V times I so what's V 230 what's I 0.4 this gives me 92. fantastic what but then calculate the energy consumed in one minute so now he wants energy now I know from unit one the energy is Power Times time so power is 92 Watts we just got that times time which is one minute time has to be in seconds so you multiply it by 60. so 92 times 60 which is 5 520 joules these have not changed very good as a final Point here there are two other versions of this formula so if you take P equals v i and you join it together with v equals IR using some you know clever math and substitution you end up with P equals I squared times r or P equals that's not a p give me a second P equals V squared over r these are simply P equals v i and we've replaced the V with ir once or we've replaced the I with v over R once you don't need to know the proof of them just know that these are two other versions of the same formula what I recommend is you don't really have to memorize these so if you do that's fantastic it will make some questions easier for you but if you already know and you've memorized P equals V times I and V equals IR you're set you're fine all right let me answer a question regarding this example we solved when do we turn the minutes to seconds when calculating energy always the unit of energies in joules that's based on the SI units that we discussed earlier and SI units are kilograms from us meters per distance and seconds for time so it has to be in seconds it must be in seconds next there's an extra unit of energy that we use at home called the kilowatt hour you probably don't see it at all unless you pay the electricity bill or you look at you know the electricity meter and you see how much you have to pay they don't tell you how many joules you consumed they always tell you how many kilowatt hours you've consumed but what is a kilowatt hour it's defined as a measure of the energy consumed by 1000 watts of power in one hour literally one key 1000 Watts kilowatt in one hour try that try the math energy is part times time what's the power 1000 watt what's the time one hour how do I convert one hour to seconds because because we need to remember that so one hour two minutes it's times 60. and then one minutes to seconds is another times a 60. so what does that give us one thousand times sixty times sixty this gives me three six zero zero zero zero zero joules all right now you don't have to memorize this but this is the value of energy the amount of energy in a single kilowatt hour so it's designed to help us limit the numbers we use at home so how do we use it to calculate your electrical Bill here's an example I tell you that the household consumes an average of 12 kilowatt hours per day so every day this is the amount of energy they use up 12 kilowatt hours the cost of electricity is 0.2 Euros per kilowatt hours how many Euros is this you could replace Euros with dollars with pounds with with uh whatever pisos whatever currency you want it doesn't matter so what's the monthly cost for this house so wait a second if I consume 12 kilowatts in a day and I want the amount of energy they use up in a month how many days are in a month one month as 30 days so the first step is we're going to multiply 12 by 30. so we get the total amount of energy so 12 times 30 this gives us 360. kilowatts hours that's the total amount of energy so what's the cost of this how much money do I have to pay so the cost is going to be 360 times 0.2 if one kilowatt hour costs me 0.2 euros and how many euros am I going to pay 360 times 0.2 gives me 72 euros and that's the amount of money I have to pay for this energy very nice so all we're saying is this you take the total amount of energy per day this is a math question this isn't really physics anymore if it takes if it's a cost of 12 if they use up sorry 12 kilowatt hours per day and each kilowatt hour custom is 0.2 pounds for example then how many pounds have you used up or how many pounds do you need to pay in a month What's the total cost so it's 12 kilowatt hours in a day 12 times 30 gives me the total energy expenditure how much energy I used now then you multiply it by the price of a single kilowatt hour so 0.2 times 360 this gives you 72 euros it's a math question more than anything else honestly it's not a physics question are we but still it's important to understand just the concept of the kilowatta next up obviously circuits or current electricity will not be complete unless we talk about resistors we have several types of resistors a fixed resistor which has a fixed resistance it just has resistance a variable resistor whose resistance changes the variable resistance resistance changes how does it change based on length sorry based on length so if you have a long resistor wire you connect to a circuit and you have a sliding contact if you move the sliding contact right and left you change how much of this wire is in the circuit so this entire wire is 100 ohms and you put the slide in contact in the middle this gives you a resistance of about 50 ohms this gives you a resistance both of tunes as you slide it to the right the effective length in the circuit increases so this takes up more space and as it takes up more space or the length increases the resistance increases so the resistance increases it's like 75 ohms for example maybe it's 80. as you move it to the left the resistance and decreases from its name it's literally a variable resistor a resistance that's fine a third Mister is also technically a variable resistor but it changes based on heat on temperature on a on temperature the hotter it is the higher the temperature the lower the resistance of the thermistry and the lower the temperature of the thermistor the higher the resistance this is completely opposite to what we said a little while ago regarding fixed resistors when we Define resistance because thermistors are made of non-metallic conductors non-metals when heated gain more free moving electrons so they become better conductors so they conduct electricity better again non-metals when heated conducted just better this is why when the temperature increases the resistance decreases if you draw a graph of how the temperature changes or FX The Resistance it'll be inversely proportional like this the ldr is short for the light dependent resistor light dependent resist them so it depends on light clearly when the amount of light hitting the surface of the resistor increases the resistance decreases it's just like the thermistor whether but it's not sensitive to temperature sensitive to light and if the light on it decreases its resistance increases it is very important to realize the ldr doesn't emit light it receives light okay it's not emitting light so when you put it in the dark or you cover it the light on it decreases so it gets high resistance and vice versa if you put it in the sun or in front of a light bulb the light on it increases so the resistance decreases [Music] very good now the last thing is not really a resistor per se but you know what kind kinda is it kind of is this is called a diode it's a diode kind of like a resistor but it only allows the current to flow in One Direction remember this is extended if the current is flowing through the diode in the direction of the arrow it goes through if the current tries to flow in the opposite direction it does not go through so it's basically a one-way gate so here's a quick circuit here's the same circuit but I'll connect the diode in reverse this light bulb will light up this will not why because this light bulb this diode sorry allows the current to go through this does not allow the current to go through because it's in the opposite direction you don't really need to remember these terms but on the diode is collected in such a way that it allows the current to go through it's called forward bias when it's in the opposite direction we'll call it reverse bias again that's not very important now the main function of a diode is to convert an ac voltage to a DC voltage so alternating current to a direct current if you don't know a direct current is the current from a battery or a cell it has a positive and negative charge the current flows through in a single Direction it doesn't change and it has a constant value it's direct this is called DC however an electrical socket or a generator produces what we call an alternating current AC what does that mean this means that for like a portion of a second a point two seconds for example this side and this is positive and this side is negative of these terminals so the current flows from positive to negative here and in the next 0.2 seconds this is positive and this is negative so the current flows in the opposite direction and it keeps alternating keeps changing all electrical sockets are AC this is the graph for a DC voltage over time this is the graph for an ac voltage over time it changes so how to use a diode to change AC to DC well it's quite simple if you just put one diode it will only allow part of the current to go through and the other part will not it will only allow parts of the current to flow through and the other part will not go through however okay however if you connect four diodes together this will completely convert an ac voltage to a DC voltage you do not have to memorize the order of the diodes just understand the flow of the current all right just understand the flow of the current if this is the AC Supply and this is the resistor that's the output maybe there's a light bulb maybe there's a voltmeter it doesn't matter take a look at this if this is the positive side of the battery and the current goes this way here it led to the right here it'll head to the right again and there we go it's gone through the resistor if the direction of the positive side of the battery or the supply has changed now this is positive I'll change the color now the current will flow this way Reach This Junction left or right it will go right and then left or right it will go right and bazinga the current has gone through the resistor in the same direction even though the supply has changed the direction of the Curve even though the supply has changed the direction of the current don't memorize this but understand that if you in an ac voltage here the output will be DC there will be no negative and positive sides of the voltage it's all the same positive positive positive doesn't change all right finally we have something called IV graphs this is literally hey um I'm curious what will happen I'm curious what will happen if we put a resistor connected a voltmeter and an ammeter and we keep changing the supply when we draw an arrow on something this means it's variable so increasing the voltage for a fixed resistor as the voltage increases the current will also increase constantly doesn't change but for a light bulb this is different as you increase the voltage the current also increases but then it doesn't increase as much take a look at this it's increasing a lot here it's still increasing a lot it's increased but a little bit it's increased a lot less why because as the voltage on the light bulb increases the brightness of the light bulb increases and if the light bulb becomes brighter its temperature increases it becomes water and since filament lamps are made of metallic conductors as it's getting hotter its resistance increases so instead of the current increasing as expected it decreases a bit doesn't increase as much as I wanted so the reason why the line slopes downward like this is because as the current increases as the current increase the voltage sort increases the brightness of the light bulb increases making it hotter and therefore its resistance increases right now the most important part of circuits before we end the electricity part the the circuits part at least would be series and parallel connections there are two ways of connecting circuits or multiple components either in series or in parallel if you connect resistors in series the total resistance will increase it's calculated using R1 plus R2 plus R3 so if this is 10 ohms and this is 10 ohms the total resistance is 20 ohms for example 10 plus 10 is 20. however the current is the same because it's the same wire so if I were to connect if I were to connect a battery here like a 5 volt Supply here and I tried to calculate the current here we go let's calculate the current here's an example right away the example is I equals V over r i want the current the voltage is 5 volts the resistance is 20 ohms so 5 over 20 this should be 0.25 so a quarter will have there same 0.25 ampere here here here because it's just one wire however the voltage of the supply is divided across the resistors it's split across the resistors and it's always split according to the ratio of the resistors so if these two resistors are equal the voltage is split across them equally try this out we already got the current flowing through this resistance calculate the voltage across R1 so you're going to say V equals IR Ohm's law the current is 0.25 and what resistance do I want you to measure 10. like the voltage across 10. 0.25 times 10 gives you 2.5 volts which makes sense because if this takes 2.5 volts this will also take 2.5 volts it's been split equally fantastic foreign but what if the resistors are not equal and I would respond by saying that's a really good question what if they weren't equal what if for example I'll keep the total resistance the same but what if for example this was a 5 Ohm resistor and this was a 15 Ohm resistor the total resistance is still 20 because you know 5 plus 15 is still 20. but will the voltage be split equally I would say not this would change the current is still 0.25 it hasn't changed because the voltage is the same total resistance same but instead of calculating the voltage across the 10 Ohm resistor no no no no I want you to calculate the voltage across this five ohm resistance so that's 0.25 times 5 which gives you come on sure you know one point two five volts if the first resistor gets 1.25 volts what will the second resistor get if I have a voltmeter here to measure its voltage what will it get the rest the rest of it 1.25 or sorry 5 minus 1.25 this will give you three point seven five points [Music] the voltage is not split equally the bigger resistor gets a bigger portion of the voltage the smaller resistor gets a smaller portion [Music] very good that's the series connection what about pattern the exact opposite the total resistance in parallel decreases so resistance decreases when you connect them in barium so if you have a 10 Ohm resistor and a 10 Ohm resistor the total resistance is not 20. instead we use this Formula 1 over R total equals one over r one plus one over R2 to calculate it or we simply say product over sum so R1 times R2 over R1 plus R2 and give this a shot here's the example 10 plus times 10 because I want the total resistance over 10 plus 10. this gives you 100 over 20 which is 5 ohms so the combined resistance of the resistors in parallel decreases it doesn't increase it decreases all right you might say yeah that's cool that's great anyway that's fine it's 5 ohms no biggie but what happens to the current if you were to connect this to again a 5 volt Supply how about calculating the total current let's go what is the total current I equals V over R the total voltage is 5 volts the total resistance is 5 ohms which gives you a 1 ampere current but here's the thing when the current is moving it reaches a junction and this causes the current to split beat isn't some of it goes up some of it goes down and when some of it goes up and down it splits does it split equally well if the resistors are equal well yeah this will get 0.5 ampere this is going to get 0.5 ampere you want to check let's do this i1 is going to be V over R1 this is 5 volts now why is it 5 volts because the most important thing with constant resistors in parallel is that every single component gets a hundred percent of the voltage from the supply a hundred percent of the voltage from the supply so if the supply is 5 volts this gets 5 volts this gets five volts because we're not sharing a current in series they used to share the current the same poor charge has to feed two resistors charge is coming here it gives this a few volts and the other one the rest of the volts but here it's got two Charges going through and each one gets its own voltage so full five volts over what's r110 5 over 10 is 0.5 ampere just like we predicted you can repeat this with I2 and obviously obviously if the resistors are not equal the the current is not split equally you can use I equals V over R to calculate them the exact same steps uh I see a few questions so just give me a second so uh how is the R5 I'm not saying in these resistors have become five ohms no this is still ten and this is still 10. but the battery behaves as if there's a 5 Ohm resistor in its way again the battery behaves as if there's a five ohm resistance way because now the battery has to double the current keep that in mind huh the battery has to double the current because you've got some current going here some current going here so it has to increase the current as it's feeding to the circuit to account for the split that's going to happen so the total current increases and as we've studied earlier if the current in a circuit has increased this means that the resistance has decreased because the voltage hasn't changed I hope this is clear okay going back will the current eventually decrease in an IV graph with the voltage increasing no it won't if I were to go back to this IV graph this will eventually plateau but it will never decrease because decreasing the current with an increasing voltage makes no sense the current still has to increase gradually but it won't increase as much but that's the problem okay very good yeah finally are there any advantages to connecting components in parallel absolutely yeah of course there are what are they well you can switch them on and off separately you can have separate switches if one of them breaks if for example you shoot a football at this and breaks then the others won't be affected it doesn't matter and finally most importantly they all get the full Voltage for example everything at home is connected and parallel everything why because the voltage at home is about 240 volts 220 240. each light bulb gets the full Voltage which is amazing and Brilliant why because imagine if you wanted to increase the number of light bulbs at home and they're connected in series when you add one more you don't get more light you get less light because each light bulb now gets less voltage eventually as you add more and more light bulbs the light bulbs won't light up if they were in series but if they are in parallel everything gets the same a voltage full 100 voltage from the supply okay okay finally what about the potential dividers what is this look at the diagram look at the side this way for example and you go like ah mister so why are you being like sneaky do you think you're clever do you think I'm do I think I'm clever this is just two resistors in series game are you playing well I'm clearly not playing League of Legends but what game what game are you playing well here's the thing here's the thing this is why we're going to call it a potential divider this is why we're going to call it the potential divider and we'll see the difference between it and a variable resistor uh if this is a 10 volt Supply What's the total voltage here 10 volts this will get 5 volts this will get 5 volts you you go ahead and say hey mister the voltage is in series that's fine it splits but here's where the fun comes in if I add another light bulb in parallel only to the first what's the voltage that it will get because parallel components all get the same voltage as each other but since the light bulb is parallel to only one resistor not the entire circuit it's not this it only gets as much voltage as the parts parallel to which is exactly what we want because sometimes I don't want to control the current I want to control the exact voltage across a light bulb for example and I want to be able to increase it and decrease it in the first case the simple potential divider you only have two resistors to do that you could have one of them be a thermistor or an ldr so now you make this light bulb sensitive to heat or light or you could use a variable potential divider this is like a variable resistor but you'll notice that both of the ends are connected to the battery so this is a 10 volt Supply and the entire wire gets 10 volts the trick here comes from where we attach the sliding contact when we connect the sliding contact in parallel not in series huh in a variable resistor it was this way it was in series because it came directly from the battery that's what I want and I put the slide in contact in the middle the voltage across the light bulb here is going to be 5 volts it'll literally be half the voltage if you move the sliding contact up here the voltage will be I don't know 8 volts it gets eighty percent of the voltage if you put your sliding contact down here it gets nothing zero volts because it's parallel to nothing so the idea here is what by changing where the sliding contact is you don't change the total resistance of the wire you change what portion of the wire is the light bulb parallel to if the light bulb is parallel to the whole wire that's 10 volts if it's parallel to the beginning of the wire only that's zero volts if it's parallel to the center of the wire I'm sure you know what that is 5 volts so a variable potential divider's purpose is to control the voltage across a component whereas the function of I'm just going back a bit the function of a variable resistor which just changes the resistance is to control the current in a circle because it's often connected in series like the variable resistors connected in series with the rest of the components a potential divider is connected in parallel to the resistor wire all right okay so again just really quickly because we need to finish our magnetism as well today potential divider just splits the voltage between the two resistors here and depending on what you connect in parallel you get the same voltage as the parallel portion only is like the area that just components your parallel to that's the voltage that you get so for example if I change this distribution if these aren't equal anymore and this gets 8 volts and this gets two volts can you tell me what the voltage across this light bulb will be since it's parallel to the bottom resistor what's the voltage here huh can you tell me exactly perfect two volts and that's why with a potential divider but instead of using fixed resistors because because the problem with the potential value is that okay I want to change the voltage now what do I do remove the old one put in a new one no that's not what I want remove the old one put the new one or you can just slide this contact up and down and just immediately control the voltage all right last part of electricity let's talk about safety electrical safety electricity at home it's used in a dimmer switch exactly this is used in a dimmer switch it does not control the current we said it controls the voltage all right just to be clear we said it controls the voltage not the current because things that are parallel to each other get the same voltage so you're connected in parallel to something that has I don't know five volts so you get five volts it's parallel to six volts so it gets six volts it's parallel to 10 volts so it gets 10 volts so by changing where it's parallel to or what it's parallel to you change the voltage across it that's pretty much it yeah electricity at home Mains electricity now when it comes to Mains electricity it's quite simple any socket has two wires that are very important one that we call the Live Wire one that we call the neutral wire in the live wire and the neutral wire because the voltage at home is always around 240 volts ac so we don't need a positive and negative Supply the difference between the live and the neutral is that the live is what's always at 240 volts you see and the neutral is always at zero volts so if I were to plug in a socket something like my PCS socket for example plug I mean and I plug it in so we connect this here we connect this here so the current goes in through this and then out through this that's the point of this live in neutral okay okay now two safety features at home very important three safety features at home because you need a oh there's a question here why do we need to get the current out because you need a closed circuit if this goes and connects to a light bulb you need a current to go in to the light bulb and back out so it can charge again if the circuit is open like you have only one part of it that's connected it won't work okay okay oops the fuse is a component that protects the circuit from an overload so if the current is too high if the current is too high uh if the current is too high the lamp is going to a blowout it's just going to burn out if the current is too low that's fine so how do you protect light bulbs or other components from getting burnt out or like you know not working by using a fuse a fuse is simply a very thin wire like this and it has a certain rating let's say 10 amperes this means that the current going through this fuse is less than 10 no problem but if it's more than 10 this fuse melts just poop Burns explodes right that instant why so it stops the current from reaching your lamp or reaching your device and burning It to the Ground so when you close the switch and the current going through is let's say 5 ampere and this is a 10 ampere fuse and it'll just go through no problem lights up your lamp no big deal but if the current is 15 ampere or even if it's exactly 10 or even if it's exactly 10 it will burn the fuse which completely stops the current from reaching the lamp now you might think it's counterintuitive like why do I stop the current this is ruined now but if uses easily replaced you can just remove the old fuse throw it away put in a new fuse and you're all good put in a new fuse and you're all good so again the purpose of the fuse is to protect your devices or circuits from a current overload by melting why because if the current gets too high it will completely a melt okay okay next what about the circuit breaker circuit breaker protects your home from an overload of current by what exactly by using electromagnet when the current gets to a high okay when it a gets to I how does that work exactly like a fuse it stops the current from getting too high and reaching your house now how does that work uh here we go first here's the live wire here's the neutral here's a switch and actually I shouldn't draw the switch upwards so it's better if we draw it down this and here's your house or your circuit and here's a magnet okay electromagnet when the current goes through the live wire and the switch is you know closed and it's fine like right now the switch is closed it's only problem it reaches your house no big deal but if the current going into your house is too high let's say your house can only handle 100 mp and then the current and the current is ATM pair that's not a problem but if it's 180 ampere what happens is that it passes through the magnet first the electromagnet first this electromagnet attracts the switch and opens it so it stops your current from going through so you see these switches inside there's an electromagnet a coil and an iron switch so when the current gets too high for your house to handle instead of letting the current get into your house instead it opens the switch for you and it stops the current from getting into your house completely however however if you want to turn your electricity back on unlike a fuse you don't have to replace it and just go and flip the switch back up again so you close the switch again electricity turns on if there's anything wrong in your house maybe there's a faulty lamp maybe there's a faulty socket anything that happens maybe there's an electrical Surge and the current rise is too high this is what's going to happen switch is going to Open click and then a your house will not get that current anymore but you're safe at least you're not going to be set on fire finally the Earth wire the Earth wire is this now we already said we have a live ad a neutral wire and then they have a third wire called the Earth over the ground wire the Earth or the ground wire what we do is if a device has a metal case think I don't know a washing machine then can a fridge your PC for example we connect the case itself to this earth so if for any reason one of your live wires touches the case the electricity flows through the case and Through the Wire and it goes out through the Earth and it goes out through the Earth which completely cuts off the a electricity like it saves you from getting electrically shocked so the way it works is that it redirects the current away from metal cases to protect you from getting electrically shocked that's all right yeah let's talk about magnetism we're done with electricity all of it let's talk about magnetism now you all are familiar with a magnet a magnet has a North Pole and a South Pole and it's a track some repels just like electric charges the concept is the same like holes repel so South and South repel North and South repel opposite poles attract North and South attract but just like electricity charges can attract neutral objects here magnets can attract certain Metals now there there's a lot more than just these two but for now Iron and Steel are the two ferrous or ferromagnetic materials that are attracted to a magnet the way it gets attracted is by magnetization they become magnetized so bring them close to a magnet it has or becomes magnetized and it becomes a magnet within its own North and South poles and it always attracts so if this is the South Pole this becomes North if this was the North Pole this would become South and then it sticks to the magnet so magnetization happens first and then it gets attracted but if you were to remove the Iron and Steel from that magnet after some time the iron demagnetizes meaning it loses its magnetism but the steel stays magnetized why because iron is what we call a soft magnetic material it's only temporary whereas steel is a hard magnetic material it's permanently magnetized okay magnets have a magnetic field just like electricity when it had electric Fields magnets have a magnetic field the magnetic field of a magnet is again a region where magnets experience a force we always draw it using Lines Moving from the North Pole to the South Pole from the North Pole to the South oops and there we go lines going out of the North and into the South the space between the lines represents how strong the field is the closer the field lines are to each other the stronger the field and the further away the lines are from each other the weaker the field however if you put a North Pole in front of a South Pole and you hold them either because this is a horseshoe magnet or just two separate bar magnets and you've held them the field lines are parallel to each other just like the electric field when it's uniform so this field is also called a uniform field this is also called a uniform field in very good the points have to come up from the edge not from the same point the lines have to come up from these poles please don't bring them up from the same point you know from different points on the same pole please now how do we see a magnetic field if you use some iron filings or iron fillings as some people say that's fine too the idea here is what is that when you have some iron powder and you sprinkle it all around the magnet it takes the shape of the field as you can see the lines of this field move from north to south now you don't know what the direction is but you see the shape and you see how strong it is here and how weak it is here if you want to see the direction of the field you use a compass with this is called a compass plotting method you put a compass here and the needle of the compass shows you the direction of the field because it is also a magnet so you mark a point where the company needle shows then you change the location of that point usually by putting the magnet here or sorry the compass here at the end of this point you see a new line put it here see a new line put it here see a new line you see a new line you see a new line you see a new line and so on so as you continue to move that Compass all around the magnet you end up with a line that shows you the direction of the magnetic field moving from the north to the South so even though I did not Mark which side is north and south in this diagram or this image this side is north and this side is clearly South forgot to write that magnets are not the only thing that produce a magnetic field a current also produces a magnetic field this is the foundation of electromagnetism if you have a current and you run it through a wire as you run the current Through the Wire as you run a current Through the Wire it produces a magnetic field around it and the field is always circular the proof of that is this as you can see in this diagram there's a wire and he run a current he run a current through it now he didn't tell us what the current was what direction was but we do know that there's a current why because when you put several compasses All Around The Wire each Compass showed me a different direction even though a compass should technically Point North towards the North Pole of the earth each current is pointing in different direction assuming that the red line is the North Pole all of these are pointing this way so the field line is either clockwise or anti-clockwise this diagram is clockwise in the other diagram it's anti-clockwise so actually the direction of the current I've drawn Heroes formed now how do I know because we have a rule called the right hand grip rule by using your right hand you give me a thumbs up your thumb is the current and the curvature of the rest of your fingers is the direction of the field so if the current is going up the field rotates and look at your hand from the top it rotates anti-clockwise but the current is going up the field rotates anti-clockwise give yourself a thumbs down right because assume I said a very cringy joke right now I can't come up with any but I'm sure I'll come up with a cringy joke in a bit so if you thumbs down wait should I say like And subscribe now I hate saying that stuff but anyway if you give me a thumbs down instead of a thumbs up your current is down going down here and the field is rotating clockwise you don't have to use your hand by the way because this is just like a screw if you screw a nail clockwise or you unscrew it anti-clockwise clockwise goes in anti-clockwise goes out exact same idea that makes it easy as you can see but as The Space Between the Lines increases the field strength gets weaker because it makes sense you're moving farther and further away from the center of the wire or this wire so the field gets weak and stronger near the center take that wire and coil it as in turns into a coil you end up with a magnetic field very similar to that of a bar magnet we call this an electromagnet or a coil or a solenoid so the field is from north to south Bordeaux as well but the difference is is that you have field lines inside the coil not just on the outside now this is actually a very important observation why because it shows us because it shows us that magnetism doesn't only come from magnets it also comes from electricity you can make this field stronger or weaker we can control how strong weak this field is by controlling the current or the number of coils so increasing the current like using a stronger battery larger battery yeah this is the right direction increasing the current increases the field increasing the number of Loops or coils use more turns that increases the strength or using an iron Port which is just putting a piece of iron inside the coil this magnetizes it and makes it strong okay how can you tell what the direction is using the right hand grip rule by looking at the direction this is the same rule but this is the North Pole and the turn of your fingers or basically your direction your fingernails are pointing to is the current in the coil so if the current is moving this way for example so it's going up going around going up going around going up going around and so on and so on and so on until it goes down that's because we connected it to a supply like this this side will be North and this side will be South how do I know using the right hand grip rule look at the current on the outer face of the coil all right if it's going up your fingernails are pointing up and they always have to be facing you as you coil your hand your fingernails are pointing up your thumb shows you the North Pole so the North Pole is on the left side if I reverse the current so that the fingernails are pointing down the current is going down the North Pole will be to the right but right now North Pole is to the left because the current is going up like this now we have two applications for an electromagnet which we call the relay and speakers so it's the relay the relay is nothing more than a component that allows a low voltage circuit or current to turn on a high voltage circuit for current there it consists of a coil and an iron switch placed Inside the Box the low voltage circuit is on the side and when the current you close the switch and when the current goes through it this coil magnetizes which attracts the iron switch so in this iron switch clicks and closes oh God I was about to close the entire thing when you close the switch the second circuit's current starts to flow and it turns on if this is the high voltage circuit so it's only used to allow a low voltage circuit to turn on a high voltage circuit next what about speakers speakers also use electromagnets by the way you know the speakers I have in my ears for example their earphones but nonetheless it's a speaker or the speaker of your phone or if you have a giant Bluetooth speaker they all function roughly the same you have a cone and when this cone vibrates forward and backwards it produces sound waves it produces sound waves the way we move this cone forward and backwards is by putting a coil around a magnet that's connected to the Core when the coil becomes magnetized by passing a current through it which contains the music by the way so we take the music signal we turn it into a current which alternates a lot and then when it goes through the coil it magnetizes the coil so it either repels or attracts the magnet that's connected to it which moves the cone forward and backwards forward and backwards forward and backwards with the music and that produces sound all right very good now before I answer questions one last bit how do I magnetize a piece of Steel and make it a permanent magnet you either stroke it what do I mean by stroke it just get the magnet and rub it on the surface of this piece of Steel until comes back just rub it in One Direction Only In One Direction and then remove it put it down move it again in One Direction remove it put it back down move it in One Direction move it put it back down move it One Direction so on as you continue doing that you're pushing the charger the North and South Poles in a certain direction this end let's say you have a South Pole that's going down here it's moving to the left this end becomes South and this end becomes normal like the end that you push down and you start the magnet stroke with goes up the next method is something I don't really like it's called hammering you take the magnet and you hold it in a north to south Direction so let's say here's a compass and here's the north to south of the earth you take a magnet and you hold it aligned with the north and south of the earth and then you bend boom and Bam start hammering it hammering it hitting it harder and harder and harder and it will eventually magnetize because it gets the magnetic field of the earth it takes the same field of the Earth however big problem there hammering it in any other orientation demagnetizes by the way this is why a method of demagnetizing is hammering as well but holding the magnet east to west this is why I don't like hammering very much it's not very consistent the best method to magnetize a piece of Steel is to get a coil and put the steel bar inside the coil inside the salon and connect it to a DC Supply so that it has a North and South Pole this will magnetize the steel inside very quickly and very strongly because remember you can just turn it on and there's no effort involved in your part you don't have to hammer anything you don't have to stroke anything it's just you just leave it there and several minutes later it's a nice permanent magnet have a nice day turn off the supply and switch it off and you take it out to demagnetize a piece of Steel you either heat it to very high temperatures you don't melt it because some people the moment I say heat at high temperatures they imagine the metal melting no just heat it until it's nice and red and hot but not melting okay okay you can hammer it as you hold it from east to west or you can put it inside a coil or a solenoid but you connect the solenoid to an AC Supply so what's AC and DC again you don't remember we said DC is short for direct current which we revised a little while ago with the diode so it's a constant Supply with a constant positive and negative and an AC Supply is a supply that keeps changing it's alternating back and forth back and forth back and forth back and forth so as it keeps alternating and changing you take this magnet and you pull it out slowly pull it out slowly that will demagnetize your supply there your magnet so AC means the current keeps alternating and why is this important because the poles of the coil will not be constant it won't be North and South it keeps changing the North and South Poles all the time they keep alternating North and South all the time so you're messing up the magnet on the inside right and then you pull it out slowly so again three methods of magnetizing stroking in One Direction I should make a One Direction joke here but we don't have the time hammering but you hold the magnet north to south because when you hold it north to south it takes the direction of the field of the Earth when you hold it east to west it doesn't take the direction of the field of the Earth that's why you can demagnetize it by hammering it east to west that's the difference and when I say East West I mean you're holding it east to west so if this is the north and south of the earth you hold the magnet sideways not up and then to magnetize you either put it in a DC coil or solenoid or put it in an AC coil or something to demagnetize but you pull it out slowly before we finish up magnetism over the next 15 minutes or so very quickly let me take a look at the rest of these things uh there are a couple of questions why don't we just turn on the high voltage circuit right away I'm sure that was regards to the relay sometimes this is not us sometimes this is an electric circuit like your phone or like an infrared sensor these are all components that are low voltage they're not designed to work with high voltage supplies but you want it to control a higher voltage Supply like an air conditioner so you've got the temperature sensor in your air conditioner that needs low voltage to work but it needs to turn on or off the rest of the motors inside your aircon so we put a relay inside to allow it to control the higher voltage circuit that's why we can use a relay that's why we need to use a relay if you didn't understand the speaker it's very simple if you have a magnet here just let's say a North Pole of a magnet here attach it to a piece of paper and then I get a coil here depending on the direction of the current of this in this coil one of two things happen one of two things happen either this magnet is attracted so it moves to the left or it gets repelled so it moves to the right but if the current here is alternating because you know it's music and the music voltage and current keeps changing this magnet continues to be attracted and repelled attracted and repelled and tractor and repel so if you have a sheet of paper connected to that magnet it'll keep getting pushed forward and back more than that more than left and that's what creates noise or sound the motion of that cone or paper back and forth so what moves it is the music the music produces a current that's alternating and the current goes through the electromagnet or coil which attracts and repels the magnet moving the speaker back and forth and we already answered what's AC and DC very good I mean honestly uh here's a good question why isn't stroking in a different direction or in different directions a way of demagnetizing I mean it does to be to be honest it is but it's though it's even weaker than hammering it's even worse than hammer so we don't add it as part of our you know options but yeah it should technically demagnetize but it's very weak so we just go like ah we don't know we don't talk about that all right moving on finally back force on the current carrying conductor we have three things to finish and I'll be going through them very quickly because to be honest I just want you to memorize certain points of these devices the the thing I want you to understand will be in a bit electromagnetic induction you need to understand it properly but the rest you can just memorize so what's this force on a current carrying conductor thing if you pass a current through a wire by connecting it to a battery and this wire is placed between the poles of a magnet this wire will move again this wire will move why because the magnetic field of the wire or the current in the wire to be specific and the magnetic field of the magnet interact so you have a magnetic field from The Wire you have a magnetic field from the magnet these two bam smack into each other and they apply a force on this poor wire over here the force is always in a Direction so that it gets pushed out of the magnet so it's either getting pushed out or down up or a Down what direction we're going to see now oops sorry we'll see which direction but the value of this Force that causes this wire to move depends on the current because you know if you increase the current the magnetic field of the wire is stronger so it moves the wire with a bigger Force it depends on the number of Loops of the wire so instead of having one wire you can have two you can have three you can have four that increases the force or we can use a stronger magnet you can replace this with a stronger magnet and it will move the wire or the stronger Force how do we know the direction the direction depends on the direction of motion depends on the current and the magnetic field we have a law called Fleming's left hand rule with your left hand you you turn your hand like it's a gun in a sense this is your index finger this is the magnetic field your middle finger is the a current and your thumb is the force okay your thumb is the a of course so North and South magnetic field is from north to south and this is the a the current so if the current is moving this way look how I hold my hand first you hold it from North to South always start to the magnetic field and then the middle finger is the current you only have one of two options it's either towards you towards your mouth so you can bite into it like why am I biting my finger ah anyway so like let's clearance towards you or the current is away from you you only have one of these two directions and it's either towards you or away from you I can see the appeal of babies sucking their fingers but never mind so anyway that sounded so weird guys move on I'll assume this is edited out and I did not say anything creepy so what's the third finger my force my thumb my thumb my thumb is pointing upwards which means the force is going to be upwards if I reverse the current I reverse the current and I have the current go into the page or this way the force is downwards so by changing the direction of the current you change the direction of the force this needs a little bit of practice but you'll practice as you solve some more questions and finally we take all of this and we design a DC motor DC motor consists of a coil is the rectangular coil you can see the animation on the right this is the coil that's going to be spinning now you have a magnet surrounding it and then you have a battery connected to a split ring and some carbon brushes the concept is simple current flows through the coil the wires of the coil experience a force according to Fleming's left hand rule this goes up and this goes down so it rotates that's literally it that's all that happens you can make it rotate Faster by increasing the number of turns or by increasing the current or by using stronger methods okay so what's the function of a split ring and carbon brush again just memorize them the function of the carbon brushes is to conduct electricity from the battery to the coil without breaking the wires of the circuit whereas the function of the split ring this thing over here that's cut in half is to reverse the current every half cycle to keep the coil rotating because here's the thing without this split ring which is half of the time touching the positive side of the a wire and half time touching the negative side of the wire without it this coil would just get stuck like it would get stuck in a vertical position like this this is the North and this is the cell to just get stuck in a vertical position and it wouldn't move so without the split ring it will not be able to rotate this is only for the motor all right and honestly this part is extended and I forgot to put the label here but just this part okay this next part which explains the generator effect must be understood because it's a very common question Pro what is induction generating electricity but yeah we generate electricity how if you get a copper wire place it between the poles of a magnet and you move the wire up and down through the magnetic field of this magnet As you move the wire up and down through the magnetic field of the magnet this generates a curve so why does that happen because when other wire look at my fingers my fingers are the magnetic field and this pen the stylus is the wire because when the wire cuts through the magnetic field lines this forces the Chargers inside to moves if you stop moving the charges inside also stop moving wait if charges are moving that's called the current and the current moves because there's a voltage so clearly by moving the wire up and down through the magnetic field and cutting the magnetic field lines I don't physically mean you cut I just mean you go through them you change through them this generates electricity this is called electromagnetic induction it's when you generate a current or a voltage when a wire or a conductor cuts through a magnetic field nobody said you have to move the wire we could move the magnet the important thing is that the cutting happens so either move the magnet or move the wire so the best way to do it is to get an actual magnet in its magnetic field will cut through the coil so as you move the magnet into and out of the coil or next to the coil it doesn't matter what matters is that this magnetic field continues to cut through the mat the coil this generates electricity or we say induces a voltage it loves that term The Examiner loves that term induces a voltage so how does that work again uh how I'm sorry how do you increase the voltage you generate you move the wire faster or you increase the number of Loops or coils or use a stronger magnet just like the motor effect just like the a motor effect then finally before we move on to the generator this is a very extra part and honestly this is also extended keep this in mind you don't have to remember the name of this law but the examiner expects you to understand the implications of this law when you move a wire for example down remove a wire down and the wire cuts through the magnetic field we have a law called Fleming's right hand law it's just like the left hand rule but with your right hand so you find use it to find the current that you generate so if you're moving the wire down the magnetic field is from north to south the current is moving this way now ignoring the law for a second either ignoring the right hand rule for a second why is the current generated in this direction there is a reason for it you want to know why because for some reason whenever you try to generate electricity by moving a wire through a magnetic field or by moving moving a magnet into and out of the field into an out of a chord I forgot to hydrate so by moving a wire up and down through a field or by moving a magnet into and out of a coil it generates a current in these things to oppose the change causing it meaning to oppose you yes you if you are moving the wire down it will generate a current that will resist you so that it tries to go up I'm not saying it is going up all I'm saying is the current that the wire will generate will be generated so that it produces a magnetic field and the magnetic field that it produces resists your emotion it's very as we say toxic hey I want to move the wire down no I want to go up okay then let's go up no no I want to move the wire down it will always try to oppose you even better here if you're trying to move the magnet towards the coil the current in the coil will be generated so that this side is becomes North and this side becomes South because it wants to resist you it's like hey I'm moving the north towards you no go away I don't like you get repelled and if you try to move the coil away if you try to move the coil away at the sort of the magnet away from the coil what will that do this will change it so that this becomes the South Pole this becomes the North Pole this will change so this becomes the South Pole this becomes the North Pole this is called lenses law and it's always it's a very minor lock to be honest and it doesn't show up very much but it has shown up last year in multiple choice questions and it has shown up the year before and I think a paper four question yeah there's one more thing that affects the current that's generated and that's the angle at which we cut the field if you move the wire up and down that's perpendicular to the field you generate maximum voltage if you move the wire at an angle you generate something in the middle if you move the wire horizontally which is parallel to the field you generate zero voltage because you're not cutting anything this is very important because the generator that we're going to see in a few minutes maybe about 10 minutes just that five attack because the generator will be a coil moving around in a circle when you move the coil around in a circle the angle at which the wire is moving is never constant it's always changing sometimes it's going up so that's maximum voltage then it's at an angle and then it's horizontal so now it's at zero but then it's going down now it's perpendicular again so it gives you maximum voltage but negative instead of positive why because the direction is the opposite and then the wire is horizontal so generate zero voltage and then you're going back up again so maximum voltage if you draw a line joining these points you will end up with an alternating current so by moving a wire or a coil in a circle not up and down like we were talking about a little while ago this will generate an alternating current with changing values and directions because sometimes it's going up sometimes it's going down this gives you maximum voltage when the coil is going to be horizontal and it gives you zero voltage when the coil is vertical because at these moments the wires that are doing The Cutting are moving up and down like we said up and down is maximum and here it gives you zero because the wires are moving left and right so left and right is zero and finally this gives us the generator if you notice do you think I made a mistake do you think these two look the same of course they do they're almost the same device the difference is what the biggest difference besides the slip Rings is there a battery or is there no battery there's no battery this is a generator we're the ones who rotate the coil we grab the coil we rotate it there could be a turbine here there could be I don't know a hamster wheel here all right there could be human guinea pigs here where we have them try to exercise you know you put someone on a treadmill have them run uh the as they run their running causes the or put them on a bike the bike causes them to spin a coil throw a magnetic field that generates electricity see we can even make humans generate electricity if we want to right and they get to lose weight win-win I'm not sure how effective that would be but nonetheless so as the coil rotates the coil cuts through the magnetic field and that generates electricity you can increase the voltage by moving it faster increasing the number of Loops or using a stronger Mac ion of the split rings and the carbon brushes is just one thing to conduct electricity from the coil to the Circuit outside without breaking it there's no need for let's reverse the direction of the current every half cycle there's none of that it's a very simple function conducts electricity they definitely have different uses it uh there's a question here how are the two of them almost identical and have different uses well here's how first this generates electricity we provide motion it gives us electricity however in a motor we provide electricity it gives us motion you get the idea it's what you decide to do it's not what the devices it's what you decide to do so you give it a battery it moves you move it it gives you electricity so you can charge your phone or a battle yourself finally the Transformer this exists everywhere by the way like I was using this right now because I was charging my phone right next to me over here I was just charging my phone so why am I saying charging my phone because the charger of a phone decreases the voltage from the 240 volts of my socket Supply down to the five volts that my phone needs how does that work here's how it works a Transformer consists of three devices I'm sorry three components I meant to see components primary coil a secondary coil and an iron core here's how it works we put an ac voltage through the primary coil the current goes through the primary coil and it produces a magnetic field you're like cool this is a magnetic field then what this magnetic field goes through the iron core and then it cuts through the secondary coil ah here that term cuts through which means electromagnetic induction is occurring we're generating electricity so when you generate new electricity or a new voltage here you get an output AC voltage now what's the point um Bravo Mr Bravo changed voltage to magnetism back to voltage so what the one thing that you can control here is the number of turns of the coil if the number of turns of both of these coils are equal nothing happens you give it 100 volts it gives you 100 volts but if the number of turns of the secondary coil is greater than the primary the voltage will increase and give it 100 volts and give it 100 volts it will give you 200 volts if you double the number of turns it'll double the voltage however if the number of turns of the secondary coil is less than the primary and give it 100 volts gives you 50 volts what's that based on the ratio of the number of turns so here's the root VP over vs that's primary voltage over secondary voltage equals NP over NS which is primary number of turns divide by secondary number of turns all right so as an example let's solve a quick example oh yeah I forgot to mention this Transformer is called the Step Up Transformer because you know it increases the voltage this Transformer is called the step down transform because this increases the voltage the other decreases the voltage let's solve this again a Transformer is needed to step down so the voltage is decreasing 230 volts to six so that's your primary voltage here's your secondary voltage the primary coil has a thousand turns he's given me the number of turns of the primary what's the number of turns of the secondary come on here's the rule NP over NS equals VP over vs okay I have the NP that's a thousand I don't know the NS VP is 230 over 6. by the way you're literally cross multiplying you don't have to use the ratio either you can just cross multiply the number of turns with its appropriate voltage and you get your answer right away so NS is actually equal to 1000 times 6 over 230. this was just math I rearranged the formula this goes up this goes down this goes up so 1000 times 6 over 2 3. this gives me 26.1 turns alright so 26 turns makes sense it's a Step Down Transformer so the number of turns is supposed to decrease not increase okay finally why do we even step up this is going to be very important that's the last thing we mentioned a power station for example generates let's say 10 000 volts a voltage at let's say one ampere the problem with 10 000 volts in one ampere is that the transmission cables the cables that transmit electricity from the Power Station to our house are very long several hundreds of kilometers long which means their current sorry their resistance is very high the cell calls the wires themselves to take some of that electrical energy and waste it as heat the wires are going to get hotter the only way to reduce this heat is to reduce the current because you want to reduce the power loss honestly you can reduce the resistance too but they're already very long you can't make them any a shorter so you can decrease the current how we put a Step up Transformer here when you step up the voltage let's say from 10 000 volts to 1 million volts the current decreases because that was a question you should have asked me a while ago which was what Mister how do we step up where do we how do I get an extra 100 volts Mr you said there's 100 volts it's now 200 volts how did the voltage increase the voltage does not increase out of nothing energy cannot be created or destroyed it's only changed from one form to another when we increase the voltage something else has to decrease in its place that's current when we decrease the voltage something else has to increase in its place that's the current because the way Transformers work is that the power that's input to the Transformer should be equal to the power output from the Transformer so the V times I remember that's we studied this a little while ago input equals V times I output so in we of course there should not be a number of decimal places here that's why I said 26 in the end but you can leave it as this when we step up the current decreases so what's the advantage here when you increase the voltage the advantage here is that number one the current decreases so number two the heat produced by the cables decreases so there is less energy lost or waste obviously we can't have a million volts reaching our homes so before our homes we have step down Transformers which drop it to our usual 240 volts whatever ampere it is we need here and that's it so what are the advantages of high voltage transmission of electricity it decreases the current which decreases the heat produced by these cables so less energy is lost from these cables and we save money in the end we can use thinner cables we we don't waste money so I don't lose energy and money here what's the relationship between I and V only in a Transformer are they inversely proportioned only in a Transformer are they inversely proportional because in a regular circuit if you increase the voltage the current increases if you decrease the voltage the current decreases was that clear excellent so last example power n equals power out as we said so the primary coil of the Transformer is 12 volts the current is 5 ampere the Transformer gives us an output of 240 volts calculate the current in the secondary coil so literally use this rule so this is what let me Mark these this is primary this is primary this is secondary I want the current so v i primary equals v i secondary so that's 12 times 5 equals 240 times I don't know so I don't know equals 12 times 5 over 240. I'm expecting the current to decrease because the voltage is increased and we would be right it's 0.25 ampere down from 5. and that's correct ladies and gentlemen thank you very much for your time and I'll see you guys next time peace