 Right on the last topic of the chapter is transformers. What transformer does? It steps up or steps down the voltage. So there are many kinds of transformers, many, many different kinds of variations are there depending on, you know, starting from how it can get cooled to how the coils are arranged, what kind of material is used, so many kinds of variations can be there. But in our syllabus, we have just with respect to design two variations, draw this and this is just block diagram, this is not exactly how the transformer looks, just like you draw the circuit diagram, right, that is not how circuit looks, but it just represents the circuit. Similarly, it represents the transformer, it is not how transformer looks. Have you seen transformer? Where? You have it in your apartments, transformer? It is there, it should be there. You cannot directly get electricity from the wires which are outside, okay. So you will have stepped up transformer near your house and stepped down transformer where the power is generated. This is edge type transformer. Is it done in your school? So what type transformer is this? Edge. So again, things are very similar to this, it will be input over here, this is output, number of turns here NP, here NS, okay. Now we are going to discuss one, I mean either of them actually, we are discussing them together now, because it does not matter what is the design, the basic principle remains the same, okay. So what happens is the input voltage comes from this side, because of the input voltage, there will be a flux that is generated over here, there will be current in the coil and current will generate magnetic field and there is a flux, okay and this flux will get transported to here and that is how the magnetic field is forming a loop, fine. Now what happens is the flux changes with time, why it changes with time? Because voltage is changing with time, so current changes with time, magnetic field changes with time and that is how the flux changes with time, okay. So flux will change this side and because of that flux change, flux changes on that side also, get it? So because of the rate of change of flux and emf at the output side is created automatically, they are not in physical contact inside the transformer, the wires are not touching but still power is able to transfer from one coil to the other and you will see the output current and output voltage, okay. This is an amazing device, similarly here one coil is on top of other but they are not touching each other. So whatever flux is changing on one coil is experienced by the other coil also, get it? Clear? So if flux coming in is 5B, okay, so D5 by DT will be same, assuming there is no magnetic field going outside, so whatever magnetic field, whatever is a magnetic field that is changing over here is experienced here also, fine and depending on number of turns, suppose here is number of turns is NP, so NP into this minus of that will be what? Input voltage or primary voltage, that is how it should be, right? Rate of change of flux should be the voltage, okay and secondary side what should be the voltage? Minus of NS D5B by DT, any doubt on this? Rate of change of flux should be same, see if you just remove primary and secondary coils, D5B will be same everywhere, now depending on how many turns you wrap it around, EMF will be different, different because number of turns you are also coming in. So if you just divide VP with VS, you will get this equal to NP by NS, so voltage in primary divided by voltage in secondary is equal to number of turns in primary divided by number of turns in secondary, okay. Now if there is no power loss, if there is no power loss then what should happen? VP into IP is an input power, this should be equal to what? VS into IS, secondary power, fine but suppose there is 20% power loss, then what will be the equation? VP into IP is equal to, what what? VP by IP is equal to? VP into IP is equal to 20% of that minus, 20% of input power is lost, so what will be the relation? 0.8 times of this will be equal to VS into IS, output will be 80% of input, but still if there is no power loss then this is correct and VP by VS is equal to IS by IP, okay, this particular equation is always correct, this one, okay and this will be equal to IS by IP also if there is no power loss, so this is how transformer works but then we have discussed only an idealistic scenario, like very very ideal scenario, all the power is getting converted from input to output side and you are able to you know live happily ever after, but this is not how it works, okay, there will be several losses in the transformer, so let's see what all those losses and from where they come from and what we do to overcome these losses or minimize those losses, write down losses in the transformer, what do you think the first one from where the loss resistors are, see for the transformer you have to use lot of coil wrapping around, okay, so there might be resistance in the coil, okay, so you have resistance of coil that can create the loss, okay, how can you minimize this loss? Use good conductor and thick wires, if you use thick wires the resistance decreases R is equal to rho L by A, so if you increase A resistance goes down second, write down flux log, flux leakage, see whatever is the flux that is created, we are assuming it goes like this and then goes to secondary, it need not be as good as like this, some of the flux may leak away to the atmosphere, right, so that is what the flux leakage is, in order to minimize this what should we do, use I type here, right, so you wrap primary and secondary coil together as in on top of each other, then somebody said eddy current, what is this eddy current loss, if there is a plate, there is a big surface area and the flux through that surface area changes, then there will be current on the surface itself, okay, as in suppose this is the plate and the magnetic field changes coming out, then there will be current like this itself, I mean it will form a loop on the plate itself, have you heard of induction cookers, they work on this principle, those cookers when you put it above that, what is that called, induction stove, then it changes the magnetic field, because of which there is eddy current on the base of the cooker, there will be a current, okay and then because of that the food cooks, because that current the loss gets converted into heat and that cooks the food, right, so it is not useless all the time, but we do not want here, we do not want eddy current to be here, okay, but from where the eddy current get the surface from this transformer, there is no problem, when you build a transformer this thing, this thing which is core is nothing but here you will be using iron or some ferromagnetic material to enhance a magnetic field, so eddy current might be in the core, so in order to remove the eddy current what you should do, reduce the surface area, so do not use full plate, use like this, so it will not get a good surface area to flow, so you can say use laminated core, what else can you, hysteresis loss, do you know what is hysteresis loss, see if you magnetize a material, what is happening here, the flux is continuously changing, positive, negative, magnitude wise everything is happening, so when you magnetize a material and then demagnetize you expect what, it will immediately get demagnetized and then it will support the magnetic field in opposite direction quickly, this core, but what happens is that if you magnetize a material and try to remove the magnetic field further, it can retain some magnetic field, that is how permanent magnets are made, fine, it retains the magnetic field inside, the dipoles inside get aligned for some time and that sometime could be like few years also, fine, so what happens is that it needs energy to retain, as in it retains it and it uses some energy for it, it does not give away entire thing back, so if you magnetize and demagnetize some material again and again, it will not give away entire energy, once you give it, it will just keep some and then give away some, because of that there will be hysteresis loss, how will you remove this, how will you minimize this, you cannot do much about it, but you can use a material which has less hysteresis loss, so that is how you minimize the losses in the transformer, so we are done with the chapter and if you have any doubts you can ask now.