 Can someone please send me individually the Topics that I have to take just take a picture of your book and send it to me Only four people have joined I'm waiting for others to join Okay, so If people are not joining till 110 then I'm going to start so Let me start let people join when they wish to I've already waited for 10 minutes for them. I can't wait more heating effect of If you remember I have given a Question also on heating effect of current in the last test So heating effect of current So let me check what today's class. I'm telling in the beginning of itself. I'm only focusing on UT So I'm not going to go beyond your book Nothing beyond your book. So I will only teach what has been there in your book So what happens? If you look at any electrical device, so when I was teaching this in class I was telling that if you look at a bulb or a tube light and if it is on for some time if you touch it It will it will feel heated because Electric energy is converted into And the same example as I see as I can see in your book It has been given in your role this thing also region for the same I have explained in the class that Because of the movement of electron what happens these electron collides with other electrons and positive ions and Which which which is as like resistance that is why resistance is there and in these collisions of electrons lose their energy and The energy is lost because collision happens and they pass on energy to positive ions and and and Other particles and as energy is transferred The positive ions will start vibrating more and and and and due to that the heat would be produced So this is the reason what happens electron is drifting if if when current would be suppose This is a current carrying conductor. So it means that electrons are Flowing from current flows from high potential to low potential. So electron will flow from suppose This is current carrying conductor electron will this is high potential. This is low potential Electron will flow from low potential to high potential in between its way It will collide with other positive ions and electrons in which it will transfer its energy to them due to that they'll start vibrating with more vigor and Due to that heat would be produced. So What happens more current means more number of electrons? Passing through what is I I is equal to Q by T and Q is equal to N E So T is per second. So one second if I take here E is fixed 1.6 into 10 to the power minus 19 So if I is increasing it means that N, which is the number of electrons drifting from drifting from low Potential to high potential is increasing. So it means that If more electrons start Going from low potential to high potential more collision will happen more transfer of energy will happen Hence more heat would be produced So if you look at your book it has been written three reasons reasons have been written that Heat produced depends on Strength of current it is proportional to I in fact I square Time for which it flows. So if It flows for more time more heat would be produced because more collisions will happen as simple as that and then resistance of wire If if more resistance is there, it means that more free particles apart from electrons are there or It is a More electrically dense. So hence more collisions and more heat produced. So H is proportional So let me go here. So This is the Thing which has been written in your book. Now how formula for heat produced is is is found out. So try to understand We know that Q is equal to IET so Work done is equal to to take any charge from High potential to low potential or whichever way you want to do work done is equal to Q into potential difference So work done. I can write is equal to IT into V now I Know that V is equal to IR. So W is equal to IT into IR So which gives me I square RT and that is why I wrote that It is H is proportional to I square H is proportional to T and H is proportional to R So this heat produced would be equal to work done From taking one charge from one place to another. So I square RT So H is proportional to I square R and T and this is only called Joule's law of heating So if you have any doubt till here, just ask me Okay, now, let me go to the other topic, which is power so What is power? So power is nothing but The definition of power is work done per unit time per unit time so It can be written as power is equal to W divided by t now I know what W is so power is equal to W is equal to I square RT Divided by T. So this comes out to be I square R Now P is equal to I square R But suppose if I don't give you current I give you only voltage. So I know that V is equal to IR So I is equal to V by R So I can write here it is V square by R in V square by R square into R So this will come out to be V square divided by R So you can use this formula for power this formula for power even if for heat generated I square RT You can write I is equal to E by R. So this will be V square by R square into R into T So it would be H is equal to V square T divided by R. So you can use this formula or this formula Okay, so I hope this is clear for you Unit units for R is so power. What is power power is unit for power is written as What so this is nothing but? what unit and Both of them would be I mean can be transformed the unit remains same for power as you know Unit of work done is Joule. So heat produced with also be Joule So any energy whether work done because energy is related to heat work done The unit would be Joule. Now. Let me go to Some bigger unit so Because what is a very very small unit? So generally you see that and why it has been written in your book that Why bigger unit is needed because? At our home try to understand Every particular electrical Machine that we are using It has specified power To it you go and check your TV some power reading reading would be written on it if you go and check your fridge some power reading would be there you go and check your check your Washing machine power reading similarly oven some power reading would be there. So how will That is why power what is not a good method to To send you your power bill because even if my fridge is suppose or or my TV is 100 watt If my TV is 100 watt How if I am not using it then that 100 watt transform into zero because zero power is used in TV Similarly, if I am using it for 30 minutes and if I am using it for two hours Different amount of power is getting wasted in using my TV. So that is why What has to be linked with some time and what is that time time of usage? So that is why electricity bill is generated and and the unit of electricity bill is kilowatt hour So one unit is known as one kilowatt hour So you we say now that this month we have used 200 units of electricity So if we have used 200 units of electricity This unit is nothing but one unit of electricity is equal to one kilowatt multiplied by one hour So one unit of electricity is one kilowatt hour and what is kilowatt hour kilowatt hour is nothing but Try to understand. So this is power and this is what this is time So kilowatt is unit of power are is unit of time So power into time both is used so that we can find out how much energy is lost so One kilowatt hour means thousand watt into our means 3600 seconds. So this comes out to be three point six into ten to the power six joules if you Produced or your electric equipments produce this much of heat Then it is said that we have used one unit of power attack at our home and this is the standardized unit to Measure the power of power uses in any home so Try to understand but power station This I was talking about power consumption how we consume power Power station where power is generated if I talk from generation side. I don't Bother whether my power is Utilized or not because it cannot be stored so hence power Generation is measured is measured in megawatts Generally, so or at home the portable generators that we have That would be in kilowatts. It can be in kilowatts also. Why because They are they require more power to supply. So that's why because here timing is not important Here the maximum capability is important because if it is running at its peak position How much power it can maximum supply that is why it it is measured in Megawatt or kilowatt here the megawatt and kilowatt does not matter because even if I am getting five megawatt from outside or something like that or Total like total Electric equipments the capacity of total electric equipments at my home is five kilowatt and I'm not using any one of them I'm actually using zero watt at my home so that is why consumption is Measured in kilowatt are and generation is measured in megawatt and kilowatt now if you have any particular doubt with you just Let me know. I'm checking the chat box now. Let me know if you have doubt Okay, the power station part what I said is Power station doesn't know that where my electricity is getting consumed So that is why or for how many as my electricity is getting consumed power is station is continuously producing the power hence the maximum capacity of power station needs to be Needs to be considered and that is why it is measured either in kilowatt or megawatt like I was working for two years in a power plant where power used to get generated so The maximum capacity of the power plant was 165 megawatt now as a power producer We didn't know that where my power is going and getting consumed So if somebody asked that how much power you can provide me we will say that at any moment We will provide you 165 megawatt So that is what I was willing to Say next topic is I was doing So electric power, you know some bigger units I have done now Ratings of electrical appliances. So you that's that's what I was discussing with you that if you go and check your Any electrical equipment at home? It will be given as like bulb would be written as hundred 220 volt and 25 watt or 20 watt or 50 watt or 100 watt Where 220 volt is saying that If you apply it means that that 220 volt and 100 watt so suppose I have an electric bulb and power rating is 220 volt and 100 watt So it means that any electric bulb if the potential difference across it or voltage across it is 220 volt the power consumed by it would be 100 watt if it is used for 100 watt, what do you mean by 100 watt? So it move it it is 100 joule per second So it is saying that if you apply 220 volt of potential difference across it in one second It will lose 100 joule of energy or to use it for one second 100 joule is required per second So if you look at so what has been given power is equal to because voltage rating has been given I have to apply this formula V square by R So power has been given as 100 watt V has been given as 220 volts or 220 square Then what is the unknown here R is the unknown here So I can find out R from here and as soon as I find out R V is equal to I R I know V R can be calculated from here. So I can also be calculated. That is what the question means Now let me go to applications of heating effect Electrical electric heating is is also produced to use light in an electric bus. So what happens is See whatever I have taught what I recommend you to read through The application of heating of light on page number 14 of your book There is nothing to be explained there just It has been told that how filament has to be made. So the materials for the materials for that as well as the fuse is given so Fuse is generally made of copper aluminium whatever copper aluminium generally we don't use iron over there We use mainly copper and aluminium for fuse So that's what it has been explained over there. So What I would you you read through it what I would like to discuss over here is Why fuse is used? Because that has not been explained in your book. So I would like to use Why fuse is used and then I'll move ahead with questions. Have you read it? Okay, Ruchita is asking that what does thermally isolated means Where it has been written Electric heating is also used to produce Thermally isolated means how it has to be Away from normal Atmospheric condition that is why they are neon gas or something else is filled over there because Only effect of electricity should come So that is what it means Okay, see whether you have read it or not. Just try to understand what happens So suppose I have a bulb in bulb. You could have seen this kind of filament now what happens if I switch on the bulb for suppose 24 hours or 48 hours or 72 hours, whatever time I'm free to do it as per my Utilization needs So what happens over here is if I The current would be supplied and as the current is supplied because H is Proportional to T as more time will pass more heat would be generated in these filaments Now it should be that strong that even in case of maximum heat produced over here and and and getting Rested over here. It should not melt. So that is why filaments are made of very strong material so What is that filament is generally made of tungsten's and Tungsten has a melting point of 3380 degrees Celsius Similarly, we have fuse at home Why fuse is used? So suppose this is the incoming to the home What do you mean by incoming? I get electricity supply from like in Bangalore. We get it from Bescom so Suppose this These lines which are these wires are coming from Bescom side so here I use fuse and fuse is Fuse is used so that try to understand and Suppose maximum current required in my home is two ampere suppose And due to any fault some hundred ampere current comes over here So what should have what what will happen if these line directly go Suppose these lines are one line is collected to my fridge One line is corrected to my TV and one line is connected to my washing machine. What will happen? They they can only tolerate up to two ampere. Suppose any wire is there Specifically in the electrical electrical equipments at home. They can sustain only I mean they can sustain current only under a certain limit so if a five ampere like ACs at Your home not more than five ampere should be supplied there so if hundred ampere is going through it the wiring inside the electrical equipment will burn so to Overcome this particular problem. So what happens instead of these lines directly going to my equipment They'll first go to fuse and wires from fuse will go to my Electrical equipment so what will happen these fuse and these fuse wires are made of either copper or Aluminium something so what will happen? If more than two ampere, so suppose hundred or not hundred ampere suppose ten ampere current is coming These wires will break automatically And if this breaks no current will reach up to my electrical equipments and my electrical equipments would be safe So that is why fuse is used So that is what it has been written in your book that if a current larger than a specified value flows through circuit Close through the circuit the temperature of the fuse wire will increase This melts the fuse wire and breaks the circuit the fuse wire is usually encased in a cartridge of porcelain so if you see generally It's a white porcelain in which fuse is there so that if any blast is there or any Fire is produced it can be contained only here because porcelain is not affected by fire. So That is what is there now you look at here the fuse used for domestic purposes are rated as 1 ampere 2 ampere 3 ampere and 5 ampere for electrical iron it consumes 1 kilowatt so nearly 5 ampere so Generally, I'm hardly hardly 10 ampere is used anywhere for bigger machines and all 10 ampere can be used But 5 ampere is generally more than sufficient. So That is what the case is now we'll move to access exercise before that I would like you to Ask me any question if you have why people are leaving and going I Not interested. Okay. No issues if you have any doubt ask me would curse One second. Just give me a moment please. Okay, so Chalo, so let me Look at the questions which are there and Then we will move ahead so the questions where On peace number You have 14 Same page. There are three questions written over there and Electric iron iron consumes Energy at a rate of 840 watts when heating it at maximum rate and 360 watt when heating it at the minimum rate the voltage is 220 volt Find the current and resistance in both the cases so Just do it all of you Try to do it Solve all the questions Then my I'll solve the third question. You solve the first question first Okay, so if you look at I'm solving the first question now if you look at The first question P max is equal to 840 watts so P is equal to V square by R R is equal to V square by P So V is equal to 220. So 220 square is 484 Double zero divided by 840. So this and this is gone. How much I get? I get 8 into 5 6 times it will not go. So let me just divide it 48 4 0 divided by 84. So let me just this will go by 4 so This will be one two one zero and this will be four divided by one so 21 so one two one zero divided by 21 So it will go five times and then it will be 57 point something So the answer is there in your book. So 57 point six ohms. It has been written and V is equal to IR. So You know that I is equal to 220 divided by 57 point six. This will not go four times So this will be 3.81 ampere and in in in this is part a this is part B is when P min is equal to 360 watts So R is equal to V square which is 484 double zero divided by 360 So this will again go by so this is one two one zero divided by nine and if you do it you will get 134.3 ohms and I would be equal to 220 divided by 134.3 that will come out to be 1.63 and yes That's simple Any doubt in the first question anyone? Okay, let me go to second question second question is more easy so second question is a hundred June and This is work done or heat whatever you want to take and R has been given as four ohms T has been given as one second So H is equal to I square RT. So hundred is equal to I square Multiplied by four into one. So I square comes out to be hundred by four Which is equal to 25 I comes out to be equal to five amperes So voltage would be equal to I into R. So that is five into four that is 20 volts question number three Question number three is See even if power rating is two kilowatts. I Don't know how much power is utilized. So two kilowatts is there and So if it is utilized for one hour a day so What kilowatt are how many units are used? Electricity consumed Daily is equal to Power into time. So two kilowatt into one So two kilowatt are is consumed daily for 30 days Conjunction is two into 30 60 Kilowatt are or 60 units. I told that one kilowatt are is one unit. So this is 60 units so as One unit Is three rupees 60 units would be three into 60 180 rupees That's the answer question number four you solve Let me know once you are solved once we have done done Utkar sir have written and written a number in the group You message on that number you will get added in some of the other group given a number of course Message on that I've written a number look at look at the previous message Okay question number four Question number four is telling me that I think it should be so work done is equal to Q into V and Q is equal to it. So we I T and Harsini, I'm solving from phase 14 So V is equal to 220 into 10 Into so 220 into 10 would give me T. I'll use later. This is power into time So I'm finding out power power is 220 into 10. How much it is? 2200 so this is in what I know unit of power at Electricity consumption is kilowatt hour. So it has to be converted into kilowatt This is 2.2 kilowatt and then It has to be so For how many hours it is used it is used 30 into five hours. So 150 hours it is getting used so 150 Power consumption is equal to 150 into 2.2 so that is equal to 300 330 and 330 multiplied by 2.5. So it gives me So 330 into 5 by 2 So this is 165 165 into 5 is a 25 rupees. That's the answer Okay, so now let me start with another topic and that topic is Nothing but magnetic effects of electric current. I have already discussed in the class Few experiments have been listed. So the austere experiment which has been listed over there That I'm going to discuss with you. You just look at the figure in your in your book I'm not drawing it because it will take a lot of time so What happens? There is a magnetic needle SN which has been shown in your book. This is on page number 15. I am talking over a stand holds a wire AB Parallel to the needle SN and is connected to a cell It is observed that when the plug keys closed a current passes through the wire and magnetic needle gets deflected When the current is stopped magnetic needle will return to its initial point So I have told you three kinds of magnetism. I just read it so that you can Get what I'm going to teach I told that magnetic magnetism in any particular Magnetism is of three kinds permanent magnetism few elements show magnetic property permanently then we have Induced magnetism. I showed how induced magnetism in the class. I have shown how induced magnetism Produced here. We are talking about Electromagnetism magnetic field produced due to electricity now this particular topic. I have done in two classes very very prominently so Austered experiment is just the part which has been written over there if in exam You are being asked that what is austere experiment the two drawings which have been made over there in the book Just made the two drawings and just write that if there is a current in the wire AB The needle will start deflecting if there is no wire in the If there is no current in the wire AB middle needle will return to its original place. That's what you have to do okay Experiment for magnetic field pattern also I have done there you just go through it. There is nothing Big on it. So I'm not getting it the formula which has been written over there B is equal to mu naught I divided by 2 pi a I have done it Thousand number of times in the class. So I'm not repeating it Right hand thumb rule Right hand thumb rule also I have been doing too many times in the class. So I'm skipping it wherever Whatever things I have done in the class. I'm just skipping it Okay, so magnetic field in circular coil has to be studied that I can do for you And then I go to solenoids Just let me check what all I need to do magnetic field lines and property I have done force on moving charge in a magnetic field. I have done then I need to do moving coil galvanometer After moving the DC motor is there in the syllabus DC motor electromagnetic induction AC generator all these things are there and Transformers just let me know Okay, fine entire chapter is there as soon as I ask whether it is there in the syllabus or not look at the response in the group my God Okay, medans. I will also teach transformers if transfer is also there No worries So Just give me a moment. Okay So magnetic field you to circular cell circular coil So if you look at the figure which has been made over there, let me draw a Rectangle for you the figure is something drawn something like this so It's something like this. There is one magnetic coil like this and the another one like this and then we have Current flowing like this. Oh, we have battery source over here and there is an Rio stat over here and Current is supplied like this. So current is going like this and current is going like this Now try to understand if current is flowing like this. I have told you how So suppose I have a circular coil here This is the coil. So in this coil Suppose I have a here and I have be here in This while the current is like this now by right hand rule you can find out the so let me read the Arrangement for you. So we have field patterns around the current carrying wire. It has been shown over there At every point of the wire the concentric circles represent magnetic field around it So what will happen is look at here? Forget about circular coil. Let's discuss about Long coil. What is have what will happen is that? at equal distance around any point there would be a circle where Magnetic field would be same if this is distance are so around this Coil there would be a circle where magnetic field would be Fixed similarly here if I increase this R. So suppose I make it R1 So this would be something like this So that is what is it is saying that around each point over here. There would be a circular If at a certain distance there would be a circular pattern like this, which is so the magnetic field out here Near point a the magnetic field lines are anticlockwise how to find out clockwise anticlockwise So you use right-hand rule if you use a right-hand rule you will find that it'll it'll anticlockwise and at at at a and then clockwise at See it has been written wrong at a it should be clockwise and and at B It should be anticlockwise I think As it has been shown in your book also and and and and and the magnetic field B is given by Mu naught n l divided by 2 R. So R is the distance N is number of tons in the wire L is length of the wire and likewise So this is what due to circular current the only thing important from the magnetic field perspective is if you make these Circles like it has been made over there. So it would be something like this Something like this something like this. What is it showing? It is showing a circular pattern of magnetic field around this particular circular wire Okay, do you have any doubt in this you can ask no, I'm unable to see the book properly. So The clockwise anticlockwise thing which is there you write as per given in the book Okay, magnetic field you to solenoid Just read it so that when I explain it, it would be simple for you Have you read it? Now look at look what happens in why solenoid first of all. Yeah so Look at here if if a straight wire is there It produced certain amount of magnetic field at a point and This is due to the complete wire So I gave you formula of mu naught i by 4 pi cost theta 1 minus cost theta 2 I have discussed in the class It was due to the whole length of wire So these many lengths this much of length suppose this this length is 1 meter 2 meter whatever it is Is not creating any addition effect of magnetic field It was observed that whenever a wire is Made made like helix different turns are given every turn acts as different conductor all together and Magnetic field if if same length of wire is added like this Then the magnetic field will keep on adding up for all the different turns over here so that is why To utilize this particular wire in better manner it can be Folded in helix it can be folded like a helix in the form of helix and we can find out that The magnetic field due to all the turns are added up in one direction and hence The magnitude of the magnetic field increases. So that is why We use solenoid Magnitude of magnetic field increases for the same length of wire now what is solenoid solenoid is a coil having Large number of circular turns and this is what this pattern large number of circular term together is known as helix form Fine and it is insulated wire the wires are insulated and When they are Won't like this it looks like a cylinder. So that is why it in in your in your book. It has been written that It isn't the shape of shape of cylinder now as I have already discussed with you that when the current starts flowing through it each of these circular circular turns act lights act like separate conductors and they'll produce their magnetic field which will get added up now What is the direction of the magnetic field the current is going like this if you apply your? Thumb goes out so from both the sides so magnetic field will always come out of This side and it will go towards one second It will go towards the another side like this So from wherever magnetic field comes out We call it North Pole and wherever it goes inside we call it South Pole so North Pole to South Pole and then What happens is? Inside this helix the magnetic field lines would be from South Pole to North Pole So always mention this that in helix the magnetic field lines comes out of the North Pole goes to the South Pole Inside the helix it goes from South Pole to North Pole. So these are the position of magnetic field lines and That is why because the magnetic field Field is adding for all the different terms It can be compared to a permanent bar magnet because the same property can be found out there So this is compared to a permanent bar magnet now the question arises that How can we increase the magnitude of the magnetic field from the solenoid? So if you increase the number of turns there is one possibility that use more number of turns so magnetic field will get added up and Magnitude will increase the second thing is increase the current because magnetic field is always proportional to current But increase in current is only up to a possible limit So we were discussing when we were discussing current rating of different equipments at our home that It cannot go beyond certain range So here also it cannot go beyond certain range because if you increase it this proportionately the wires or the Wire which forms the coil will burn out So that is one case so that is why in case of solenoid only The magnetic field property has to be or if more Current is Supplied to the coils it has to be cooled down properly So it can be water cooled or some other some other gas Can be used to cool it Now polarity I have already discussed so North Pole and South Pole I have already discussed looking from the face of the coil the Current around the face is clockwise direction to the Face represent South Pole. So see what happens is it's a general rule If if there is an electromagnet magnet so Electromagnet means current is supplied to the conductor So if if you look at the conductor from one side and if if you find that current in the conductor is in clockwise Direction that face of the conductor would be South Pole. This this is common for all Electromagnets. This is not only for solenoids. So always remember if electric current is supplied to Electromagnet from whichever side the Face is is is like the current is getting supplied in clockwise direction That would be South Pole from whichever side the current is is getting supplied. I mean you it looks like current is supplied in anti-clockwise direction that would be North Pole. So we need to understand that and Magnitude remains the same now. Let me go to A Fleming's left hand rule just mug it up from their IBL sine theta I have already done now Let me directly go to a moving coil galvanometer all other things I have done Just ask me any questions if you have what I have to repeat. Let me know Tan maya, what should I repeat? I'm trying to say that whichever side suppose in any conductor suppose This is a circular conductor and if I look at from here and this this current looks to be going clockwise If the current looks to be going in clockwise direction this side will be the side which I am facing is South Pole of of this electromagnet from other side if you look it will it will look to be going in Anti-clockwise direction. So the other side would be North Pole So that is what I was explaining that in any electromagnet if you look it from a side From where the current is going clockwise that side is South Pole if you look it from a side from where current is going Anti-clockwise that is North Pole as simple as that The third method of producing large magnetic field in solenoid is to increase the amount of current Which is flowing through it, but you cannot increase One second, what is the third method mentioned just wait for a moment So if you include the soft irons it There would be another effect of induced magnetism through soft iron. That is what it has been written over there There is nothing to be explained It's itself is a conductor Okay, so let me go to moving coil galvanometer Now I request all of you to just go through moving coil galvanometer Till the time you are reading it. Let me make moving coil galvanometer on the board read it all of you This is very important. This is North Pole. This is South Pole This is Torson head H this is suppose coil ABCD in between there would be a soft iron core over here. So this is soft iron core This is my copper wire, so I mark it a B C and D so I can write this as Copper wire and then I have a concave mirror over here Now the basic principle of moving coil galvanometer is that whenever a copper coil will so suppose The current is is flowing like this Current is flowing like this. So it would be like this here now what will happen is suppose a Copper wire is here and current is like this and and and like this So magnetic field is uniform from North Pole to South Pole So if you if if magnetic field suppose is going inside So what will happen the direction of force is I into L into B So I is like this B is like this so you can see that force would be on This side here and on this side here. So Forces in opposite direction you might have read it in class 9 is this will provide a torque and due to this torque this will start moving so The actual thing is The current carrying coil kept in magnetic field experience a couple So this torque is known as couple couple means Presence of force in opposite direction on one body and due to that this will start rotating So couple will create a rotating effect, which is proportional to the current It is used to detect and find the direction of flow of current and And and and voltmeter and ammeter so when we discuss about how to change it into voltmeter and ammeter I'll discuss that now. What is the construction construction is in front of you? We I'm sorry, we have rectangular coil, which is copper made of copper and Insulated copper we have and this coil is kept in between this north and south pole and One portion of The coil is attached attached for Balance it has been attached with the torsion head a small mirror is attached To it. This is to Why mirror is there? This is very interesting. This is not an optical instrument No, so mirror is there to observe the deflection or produced by the coil How much deflection is produced by the coil to observe this we have this mirror So when coil will you have to ask me when coil will Produce any particular deflection there would be no deflection if current is not there So deflection will only produced in presence of current the current enters to This torso head and leaves through spring So it has been shown over here that current will leave through here and it there would be deflection produced over here As simple as that so there would be deflection here the complete coil would be deflecting Why now the the question is why the magnet has been made in in the concave shape like this shape like this so Mac see the reason behind making it concave is that Magnetic field is always parallel to the plane of the coil So if magnetic field is always parallel to the plane of the coil if it is not parallel then the Couple produced would be not uniform. So that is why a uniform mag to produce a uniform Magnetic field this has been made Concave so this is the working sorry construction of this now. What is the working of moving coil galvanometer? Working of moving coil galvanometer is this ABCD coil ABCD is as you can see in the diagram Coil ABCD has been kept in the magnetic field So if if this is like this so now suppose this current is like this so I Is on this side B is on this side so l into B if you do some couple would be produced so F is equal to I L B sin theta if this is in this direction and current is going in this direction Theta would be equal to 90 degrees. So this always remains perpendicular So in working first you have to say that ABCD has been kept in in in directions such that The angle made between current and field is 90 degree or you can write that the current and field are Perpendicular to each other if current and field are perpendicular to each other the direction of the current in a B and C D are equal and opposite therefore both experience I Have already told you that they'll experience force in the opposite side and hence they will form a couple Now you can ask me that why I am I'm talking about AB and CD only why not AD and BC Try to understand current would be like this here and current would be like this here in BC now current and Magnetic field are in same direction in BC. Sorry in CD and or AD and It is in opposite direction in BC So either it will be theta is equal to zero or theta is equal to 180 degree and the force applied in these particular Conductors or or a length of wire AD and BC would be zero So that is why only two forces would be applied on the sides AB and CD So and as the couple has been produced, it will try to rotate the coil. This is called deflecting couple So I have already told you these things What happens when when the couple rotates the suspension wire, which is there and This this is the suspension wire and this is spring will get when it will start rotating the spring will start getting twisted and When the spring will start getting twisted so What will happen is this will provide an opposite couple when when the spring will start getting Twisted due to inertia that the opposing couple will be there, which is called a restoring couple So this starts rotating in certain direction due to this This will start getting twisted. It will oppose it and due to opposition of the rotation of the coil Restoring couple will start Now what will happen? This is very this is made. This is spring is made of phosphorus brown bronze and Why it is made of phosphorus brown bronze because it has very high tensile strength So even if it is rotated very Rotated very briskly what will happen? It will not break down if it breaks down. We will be unable to Measure the rotation effect so Try to understand when the moment of the force produced by deflecting couple is equal to moment of I mean what will happen is it will opposite in one direction the Coil will try to opposite in another direction and when the two couples or the two Forces are equal at that point of time coil will rest in in in a new position. So suppose coil Is moved or coil is rotated by angle theta So tan theta is proportional to I or I can write that I is equal to K tan theta so Try to understand That we can find out the current from here that how much current is flowing through it by K tan theta So I will explain it once more. Let me go to construction Construction is like that. There are two permanent magnets North Pole and South Pole why it is concave It is concave because a uniform magnetic field parallel to the plane of Coil can be produced. We have a coil which is made of insulated copper wires and It has been rotated in rectangular shape It is fixed to a Torson head edge and the current enters to the coil through torsion head edge. Now what happens is We have a spring which is made of phosphorus phosphorus and bronze and Why phosphorus and bronze has been selected for this spring because it has a very tensile strength and even if The rotation of the spring is very high and very brisk Because of very high tensile and strength. It will not break Now what happens is? In after the construction we can go to the working of it. We know that If current is passing through any particular current carrying conductor which has been kept in external magnetic field The force applied on it would be I L B sin theta now. There are four different conductors. We can look at here a B BC CD and AD so the force will be applied only of a B and CD because here the Current and the magnetic field are perpendicular. It is the force will not be applied on BC and and AD Because current and magnetic field are parallel to each other. Hence theta would be 0 or 90 and force would be 0 Once the force is applied The force would be in opposite direction on the coils on the wires a B and CD Hence as the force generated are in opposite direction or couple would be generated due to this generation of couple the Or a torque whatever you may say due to this the coil will start rotating in certain direction as the coil starts Rotating in certain direction. It will start rotating this is spring also but this spring will oppose this rotation finally what will happen in this rotation and opposition of rotation at one particular point when the Restoring couple and and moving couple both are The amount of both the couples are same then this particular spring will rest at certain position and From there the change in the position of or the angular change in the position of spring can be found out If that is theta then we know that tan value of that theta is proportional to current flowing through the Through it so I can write that I is equal to k tan theta and from there I can be found out Any doubt in moving coil galvanometer? Any doubt in moving coil galvanometer? Okay, so as I was explaining Moving coil galvanometer. Yes the mirror thing I missed. It's a concave mirror just to see the deflection inside the Inside the coil nothing else mirror use of mirror is to see the deflection how much deflection is there. That's it The tan part Ruchita it is if it is not there in the book don't write it in the exam I'm saying that this is spring will get a reflected by a sorry deflected by an angle theta the amount of this tan value of This theta is proportional to I more the current more deflection will happen. So I Propositional to tan theta So I can be written as k tan theta as simple as that where k is a constant okay, fine so I Hope moving coil galvanometer you understood properly now. Let me go to convergence So conversion of moving coil galvanometer and we have a class on Saturday. So don't miss the class on Saturday I'll again revise these things for you on Saturday. So whatever I can do till 3 o'clock. I'll do it rest all I will Do it on Saturday? So where is Conversion because a lot of people what I feel is that only half the people are are attending the class today so My wish is that the all these conversions and and and transformer these are the only two main topics left out if possible, I would like to do it in the class on Saturday because a lot of people now as you know moving coil galvanometer those who have attended the class will understand emitter and Voltmeter easily there is absolutely no doubt about it So I would like to take it in the class on Saturday So that everyone can can Can be part of discussion only few people are attending the class I I thought the attendance would be a hundred percent because it was an immediate class so What do you say? I think we should be I think we should be Doing These topics in the class because a lot of people are not there. What do you say? Okay fine, so I teach I Take those classes in those topics only three topics are left out electromagnetic induction and and then we have Conversion and transformers won't take more than one hour of time So I'll take it on Saturday. So see you on Saturday. Don't bung the class that day Thank you so much