 So, write on a JML chapter electromagnetic induction, again the chapter name is bit so we call it in a short form EMI, so you will keep on hearing this chapter name as EMI. This chapter theory is very less, but the best thing about this chapter is that this is a junction of many chapter, there will be concepts from current electricity getting used here, there will be concepts of moving charge magnetism getting used here, there will be concepts from electrostatics getting used here and then on top of it entire mechanics which you have learned in class 11, even that can be used up here, fine. So, some of the very nice questions can be made out of it because multiple concepts can be mixed to create a question, so some of the very nice question you will see from this chapter itself. And this chapter as a name suggest is electromagnetic induction, this is the first time you are studying the phenomena of electric field and magnetic field together, what I am trying to say is that the first two chapters in your NCR team, they are devoted to what? Electric field and whatever is the phenomena related to that, second next two chapters are devoted to magnetic field, fine, this is the first chapter which is like combining electric field and magnetic field, all right and one more thing I mean which you should know that you know at your home, what the electricity which comes in, right, it is like alternating voltage that comes in, all right, so basically that alternating voltage is created by an AC generator, fine, so you know it is very difficult to create voltage, like for example if I ask you to create 200 volts, you just take 2 volts battery, 100 battery you connect in series, you get 200 volts, but that is not how you want to do it, right, but then one amazing thing about magnetic field is what? That if there is a magnetic field due to a circle coil which is equal to 1 tesla, you want to make the magnetic field double, what you should do, increase the number of turns, just have one more turn, magnetic field will become 2 times, but that kind of arrangement is very difficult when you talk about electric field or potential, fine, so increasing magnetic field is very easy, in fact if you put some ferromagnetic material where the magnetic field is there, your magnetic field can get enhanced up to 1000 times also, like soft iron core have you heard of it, they put soft iron core because it is soft iron is a ferromagnetic material which enhances the magnetic field, it becomes very easy to enhance the magnetic field and make it like 10 times, 1000 times, 10,000 times, right, will increase magnetic field without doing much, without making lot of effort, so if you know a method which converts magnetic field into electric field because magnetic field created creation is very easy, so if you know a method to convert that into potential difference or electric field, when you are done, right, your ultimate requirement is what, potential difference which you want in your home, right, creating magnetic field is easy, so if you are able to convert magnetic field into this thing, then that is like the best invention possible for you, isn't it, so before this AC generator came in, people were using DC power, so this is the Thomas Elvin edition, okay, this was the guy who has actually commercialized the electricity, so he has also founded a company, General Electric if you have, so he was the one who used direct current to give power to the homes, alright, so that thought did not struck to him that he can convert magnetic field into electric field and generate potential difference, so he was like, okay, using chemical energy and trying to convert chemical energy into electrical energy and he was getting ahead with that and he made lot of investment related to that, at the same time there was this Nikola Tesla who used to work as an employee inside his company, so Nikola Tesla suggested him that, you know, alternating current can be better, okay, so he was like making fun of Nikola Tesla and he was like jokingly told him also that if you create a model or something, you will get some $5000 to do something, alright, so he, Nikola Tesla went back and actually came up with, you know, a model of it, so there was lot of idea clashes between Nikola Tesla and Thomas Elvin edition, so of course Thomas Elvin edition was the owner of the company, so he was like not liking it because it was also getting into his ego, so he asked Nikola Tesla to leave, okay, Nikola Tesla was not very rich, so he struggled a lot to make his attention, so he actually used, once he was working for the Thomas Elvin edition company to lay his table, so he used to dig holes for the wires to, then during that time itself one of the investor or one of the guy who had a lot of money, he heard Nikola Tesla talking about this phenomenon of alternating current and how it can be generated, so that interested this guy, so Nikola Tesla then got a support, monetary support which he wanted, right, so then he could develop his idea a little bit but then of course by that time Thomas Elvin edition company also grew very big but the main problem Thomas Elvin edition was facing was not generation of power, it was transmission of power because DC current once it is created and if you have to transmit to a larger distance you cannot decrease the current without decreasing the power, so if you want to pass the lesser current you need to decrease the power, why you want to decrease the current is because there is a power loss in transmission in the wire that is I square r, fine, basically you want to decrease the power, sorry decrease the current and then increase the current later on at wherever you want to use it, so you have transformer in almost every apartment, so you have a very high voltage coming but current is less but V into I is constant that is power, so the transformer at your end will decrease the voltage and increase the current that is not possible with DC and when Nikola Tesla was building his idea about the alternating current even he was not aware of transformer but when he got to know that someone in Europe had invented this thing called transformer then there was no stopping for the idea of alternating current because using this transformer you can transmit the electricity from like 10,000 km also, right, so not 10,000 sorry around 100 or 500 km, still there will be power loss, right, even if you decrease the current, so that actually completely transformed but then if DC current would have been there then you would see the power plant almost every corner of the Bangalore because you cannot transmit more than few kilometers, power loss is so much, so alternating current which is the outcome of this thing converting magnetic field into electric field has completely transformed our lives and that is why it is very, very important, right, fine, so let us start the chapter, now of course this chapter is basically talking about that the idea of electric field and magnetic field can be unified because one can be converted from other, what does it mean, there are just two sides of the same coin, all right, so since it is unification of these two ideas and people in earlier time they used to think that electric field is completely different and magnetic field is completely different, they used to study it separately, so the discovery of this is incidental, it was not that someone is doing research, systematic research and found out that you don't know what you are doing basically and luckily you found out that yes, it can be converted, magnetic field can be converted into potential difference or current, whatever, fine, so this chapter starts with few observations itself, like what all observations people have made and what all inferences have been drawn, fine, so we will also start like that, fine, so we will talk about few experiment, we will see what all conclusions can be drawn from those experiment and then we will come up with some mathematical expression and after that it becomes straight forward, right, so this is experiment number one, right now and you guys like if you think that you are not getting sufficient time or whatever it is immediately after your school you can come here during non-sentence days, getting it, like for example you don't have centre on Monday, Wednesday and Friday, you can come here immediately after school or when you have holiday you can come in the morning here sit through the problem solving with them, they are also coming again, you have to become very serious about whatever you are trying to achieve, fine, so I am connecting a gallon meter out here, this is gallon meter, see of course the way we are conducting experiment, I mean the way we are talking about experiment things have not been done like this in a systematic manner, right, so we are just talking about those experiment which makes sense, fine, but then to arrive at these experiment, lot of other bad trials or bad experiments have been done because if you are not aware of what they are trying to achieve, right, suppose you have a magnet like this, north and south pole like this and you have a coil, so what is observed in this experiment is that if you move the magnet, the coil is like this facing the magnet, coil faces the magnet, so if you coil like this and magnet comes near the coil, the gallon meter shows the deflection, what is the observation, gallon meter shows the deflection, fine, so what you can conclude out of this experiment, first of all there is a current, right, first of all there is a current, so can you draw some causal relationship as in cause and effect relationship, what causes the currents and that will be your actual conclusion of the experiment? Motion of the magnet. Motion of the magnet creates the current, simple, let's keep it very very simple, okay, if you just talk about this experiment, the conclusion should be the motion of magnet creates the current, fine, this is experiment number 2, now experiment, sorry, this was experiment number 1, now experiment number 2, okay, what you are doing is you are putting this as velocity v and the coil is also moving with velocity v, okay, now the gallon meter shows no deflection, no deflection, so what should be the conclusion here, see now the thing is whatever conclusion you make now should not make your observation 1 as wrong, are you getting a point, whatever conclusion you make should be a subset of conclusion 1, so what is that conclusion now, what do you think? Relative motion. Relative motion, it is a relative motion between magnet and loop that creates the current, see when I say that current is created, automatically it means that emf is created and electric field is created, are you getting it, so basically I am able to generate electric field out of magnetic field, now this is experiment number 2,