 okay guys so as I was supposed to take class on few topics so I'm just going through those topics and I'll stop the class let everyone join only four people have joined so I'm just going through those topics and I'll stop the class let everyone join so I request all of you to kindly sit with your physics book because mostly I would be referring that book only because this class would be focused on your exam is anyone else joining okay I'll start the class no issues people are not joining then I cannot do I cannot help it out so the first concept that I'll be taking up today is moving coil galvanometer so what is a moving coil galvanometer why it is used what is the usage of it so moving coil moving coil galvanometer is a kind of amateur what is the use of amateur to find the magnitude of current in any current carrying conductor now then why do we need moving coil galvanometer so moving coil galvanometer will not only tell you it will tell you also about the presence I mean if it tells the magnitude of the current presence of the current is established it will tell you two other things so it will tell you two things so it will talk about I and it will talk about direction of the current so first thing first about moving coil galvanometer it gives you two things it gives you magnitude of the current it gives you direction of the current now try to understand here let me download a moving coil galvanometer now look at this this this is moving coil galvanometer and how it is constructed so I'll talk about construction of the moving coil galvanometer so in constructs construction of the moving coil galvanometer you have two terminals so here you see you have two terminals here one is your positive terminal and second one is your negative terminal and then you have these magnets so this is your south pole of the magnet and this is your not this is your north pole of the magnet and this is south pole of the magnet now this magnet is a kind of cylindrical magnet so why do we need cylindrical magnets here though it looks bar magnet here generally we use cylindrical magnet over here we need cylindrical magnet in this particular construction because we need radial direction of the magnetic field to be radial why do we need direction of the magnetic field to be radial because suppose you try you understand that suppose in between you can see here coils my conductor coils are kept over here so these these coils are copper coils which are insulated thinly and in between you have a iron ore or a soft iron cylinder which is placed inside it so what happens over here is that when our external magnetic field as I have already told you in the class that whenever an external magnetic field would be there and a current would be applied to the conductor the conductor will feel a force which is I L cross B now what do you what do I mean by radial magnetic field so I'm removing this particular so look at here what happens suppose I have a coil like this so magnetic field is radial it means that plane of the current carrying coil is in direction of the magnetic field so this is the plane of the current carrying conductor and this is the direction of the magnetic field now what will happen if the plane of the current carrying conductor is is in direction of magnetic field suppose this is B1 so on these two particular wires I will not feel any or on these two particular wires there would be no current applied sorry no force applied because if F is equal to I L into B if I and L are in same that sorry L and B are in same direction so angle between them would be 0 degrees so the force applied would be 0 while on other two conductors there would be force applied so what will happen on this conductor suppose current is going in this direction and these in this direction so if I use right hand rule so I'll put my fingers in this direction and I'll put Pam in this direction so a force upward would be applied here a force downward would be applied so what will happen because one force is acting like this and one force is acting if I take correct complete coil like one one wire like this from one side the force would be applied like this and from one side of the force would be applied like this so here if the force is in this direction or upward direction here the force would be towards downward direction so what will happen due to this force acting on two different coils force acting in two different direction the coil will start rotating and as soon as the coil will start rotating what will happen is that here is the elastic spring so what happens as soon as this coil starts rotating there would be some tension which will be developed in the in this elastic spring so due to this 10 develop I mean as soon as the tension develops in this elastic spring and this coil starts moving in this particular direction suppose it goes in this direction so what happens this will make certain angle with horizontal this particular spring and this angle can be measured out as soon as I measure out this angle so that there is one formula I just give you the formula so in class 9th you might have studied torque so what happens when two forces are acting something like this so what happens there would be torque developed on this body and due to the torque developed this will start rotating the same will happen with the coil that's what I was explaining on the other page that whenever a radial magnetic field will cross this current carrying conductor so on the parallel wires there would be no force but on the vertical wires there would be opposite force from two sides due to this kind of opposite force a torque would develop due to the torque this spring would get elongated or this spring will make certain angle with horizontal or vertical whichever angle you take so what is the torque developed torque developed would be n n is the number of coils I because this is the total amount of current into B and multiplied by a and that this torque would be equal to whatever is angle whatever angle this particular thing is making this is not given in your book I am explaining it from my side so that you can understand how do I measure current I know number of coils in in the conductor I know what kind of magnetic field I'm producing I I know the value of a I just measure the value of theta here and as soon as I measure the value of theta so this torque would be equal to C theta which where C is torsional constant so if it is a torsional constant what will happen so if it is a torsional constant I know the value of constant also so from here I can find that I is equal to C theta divided by NBA so I know all these quantities that's how I can measure I from here so this is what moving coil galvanometer is is there any doubt in this any doubt tell me guys so once again guys give me a moment is cross sectional area and C is torsional constant you don't need to know the value this is a constant which is called constant of torque or torsional constant so I'm not giving you values of this you just understand that here as soon as the torque will develop this will start rotating due to rotating this this spring will lose its initial condition and it will make some angle theta as soon as it makes some angle theta this can be this can be measured out as soon as you measure it out as soon as you measure it up measure it out you can find out the value of I so that is the thing so I'm moving to the another topic where leveling screws has been given Ravi Kiran let me go through your this thing time see I'm getting so many question age cross sectional area of the of the coil material and C is torsional C is torsional constant I'm not finding Ravi Kiran where in the picture what you are asking leveling screws where are leveling screws see it it has been placed on this this particular thing is placed on certain base so leveling screws are not for this leveling screws are to put this base in proper manner so that the base doesn't start moving here and there that's what is for base the construction is here this is the construction of your moving coil galvanometer you just know the construction that this these are the magnetic fields which provide external these are the poles magnetic poles which provides external magnetic field this is the moving coil galvanometer radial magnetic field is produced like this why we need radial magnetic field I told cylindrical I'm sorry it is hemispherical so hemispherical in nature this this these poles are hemispherical in nature which are able to produce a radial magnetic field due and when you pass a current through it what will happen force would be applied on the coils of the conductor so parallel coils will not have any any any any force vertical coils will have I mean these wires will have force these wires will not have force and due to force acting on two ends of this complete coil arrangement there would be torque developed into it due to the torque this will start rotating as soon as it will start rotating so this particular spring will have certain angle with horizontal so this is the formula and Nib a which has been given equal to see theta so from here I know theta I know see so I can find out the value of I that how much current is passing through it so as simple as that so any other any other particular concept that you want to know tell me so I'm not getting any reply so let me move ahead what else do you want to so now conversion you can already see it has been given in the question that once again I'm okay what is the other topic I'm just going through the list of topics just give me a moment so now there is a concept of electromagnetic induction so now I'll teach you electromagnetic induction and what happens in electromagnetic induction so what is electromagnetic induction a little bit of brief I have already given it to you so what happens in electromagnetic induction so I'll in this particular thing I take moving coil galvanometer I have already taken so I will be taking your electromagnetism and generators and motors all these things I'll cover up cover up now so let me go to electromagnetic induction now so let me make the diagram for electromagnetic induction so till now what we have studied is whenever a current carrying conductor is placed inside a magnetic field a force is applied on the conductor now suppose I have kept a coil this is my current carrying conductor in in form of coil and I have a magnet here suppose whatever you take North Pole and South Pole like this so suppose distance between it is D and I don't touch this magnet so certain magnetic field would be crossing this particular conductor now what I start doing for experimentation is that I keep on changing the distance between this coil and this magnetic material continuously so this will never be D it will always keep on changing if I keep on changing distance between this magnetic material and and and this coil what happens is the amount or magnitude of the magnetic field or the magnetic field lines with which would be crossing this particular coil will keep on changing always and as it will keep on changing always what happens is due to remember always due to change in magnetic flux crossing a conductor a voltage difference which is also called emf electromagnetic electromotive force which which which I'll not use emf I'll use voltage also a voltage difference would be a voltage difference would be induced in this coil so what is happening what I am doing I am I am putting this particular current carrying conductor in varying magnetic flux and due to this varying magnetic flux a voltage difference is induced across its terminals so what happens this kind of electromagnetic flux which is induced due to change in magnetic flux is is known as electromagnetic induction why it is known as electromagnetic induction so suppose there is no current in it so let me draw again draw it again suppose there is no current in it I have just kept this current can I just kept this coil like this there is no current I is equal to 0 initially now what happens when I place this particular coil in a magnetic field which is varying changing electromagnetic flux means either the distance between this and the magnetic pole or magnetic material is changing or somehow I am changing the magnitude or the direction of the magnetic field passing through this particular current carrying coil due to change in this magnetic flux what happens a emf is generated or a voltage difference is generated if voltage this voltage difference is generated what will happen V is equal to IR so this V is induced in this particular coil because of changing magnetic flux as this V has developed this particular coil will have certain amount of resistance in it and due to it a current will start flowing through this conductor if the circuit is closed and the value of current would be I is equal to V by R so that is what electromagnetic induction is now the other rule of electromagnetic induction is that the whatever this voltage difference so whatever V is induced it is directly proportional to the rate of change of flux so if I assume that try to understand if let's say that the flux is suppose I denote flux by Phi suppose I denote flux by Phi so what happens this Phi keeps on changing so V is proportional to rate of change of flux rate of change of flux would be D Phi by DT so V I can write down as D Phi by DT now try to understand there are two three things that I would like to clarify over here the first thing that I would like to clarify is the emf around this or the voltage difference around this particular coil is created getting created only because varying magnetic field is crossing it as soon as the magnetic field becomes constant this voltage difference will become 0 so till till when the voltage difference will exist the voltage difference will only exist till the time the magnetic field is varying if there is no if there is constant magnetic field there would be no voltage difference which would be developing across this particular coil now what about magnitude of the voltage difference magnitude of the voltage difference is proportional to the change rate of change in the magnetic field so these are the two things that we need to take care of while we study electromagnetic induction so as we discussed this electromagnetic induction application of electromagnetic induction can be applied on or can be studied through the concept of electric generator so I'm getting into electric generator so let me check in your book what kind of generator it has been given so AC generator has been given in your book okay part from it what has been given okay lens lens law has also been given guys give me a moment hello yeah sir good afternoon tell me okay yes sir what happens is my class and Raghavendra class both has been scheduled in same classroom 316 but but because the next classroom is empty so sometimes I go to the next classroom or no not opposite just just just behind 316 which are whichever classroom is there so okay no it's not next to Mr. Pawan's office it's next to the washroom yes so just near to miss Sonia's office 3 room number 316 is there and and and no I don't go to the opposite room also no not near the staircase on one side we have this toilet on the other side there is a classroom so across the aisle on 317 or 318 one of them right in front of the lockers that that's the same no I don't go Raghavendra is going now to the that class yes yes okay what a what an urgent call so let me take you through the Lenge's law what is Lenge's law so try to understand what Lenge's law says that direction of the induced current is such that it opposes so it's actually Newton's third law or law of inertia whatever you can say Lenge's law is application of law of inertia or every action has equal and opposite reaction so by Lenge's law what it tells that suppose this is my conductor and there is a varying magnetic field which is coming like this and it is crossing my conductor and due to this a voltage difference is produced across it and due to this voltage difference a current is produced in this I have already discussed it now what would be the direction of the current so Lenge's law defines the direction of the current produced in a current carrying conductor because of when or when it is put inside a change in magnetic field so Lenge's law tells me that the direction of the induced current this current which is getting induced due to this varying magnetic field VMF would be in such direction so that it can oppose the change which produces it it means that whichever magnetic field is producing this particular current inside this conductor the current would be in such direction so that it can oppose this magnetic field so what happens is that or let me directly go to how to find out direction of current so direction of the current by Lenge's law can be find out by Fleming's right hand rule Fleming's right hand rule tells me that suppose this is your thumb this is your thumb this is this is your index finger and this is your middle finger so middle finger or middle finger I will make it make it like like this so middle finger shows the direction of the induced current and though your index finger or forefinger will tell you the direction of the magnetic field and your thumb will tell you the direction of the force or the motion because motion will be always in the direction of the force so what happens is that in Fleming's left hand right hand rule we have three we take three fingers the three fingers used are I am writing here the index finger tells me the direction of magnetic field middle finger tells me the direction of current and thumb tells me the direction of induced sorry motion or force so this is how it is so Lenge's law is all about determining the direction of the current induced and the principle to determine the direction of the current is that the current would be generated in such direction so that it can oppose the incoming or the crossing varying magnetic field so the current would be developed in that direction so that it can oppose the magnetic field which is due to which this current is created and for that I have Fleming's right hand rule so I have given you three fingers you can apply that and you can write it down in exam now let me go to alternating current gen generators or dynamos alternating current generators are also called dynamos now in your book a figure has been made let me check the page number for you on page number 29 all of you just go to page number 29 no real motion does not refer to the motion of magnetic field it's not see the motion which has been kept over there or the moment which has been kept over there is not the motion of the magnetic field it's the force which is getting applied so actually even when the current carrying conductor you know that a current has started flowing on in the conductor and it is placed in external magnetic field there would be a force developed in that magnetic field so that's the direction of the force as simple as that okay so all of you go to page number 29 of your book so a construction has been given I'm just reading the construction and I'll explain you from your book itself so what is the construction given so as I start AC generators AC generators are also called dynamos now what is the main function of generators so electric generators convert mechanical energy into electrical energy and alternating why it is called alternating current generators because the because if electrical energy is getting generated so what kind of current is getting generated into it so it is called electrical sorry AC current generator because the output of the generator is AC current so you should not feel that input is AC which it has been named AC generator because the output the current which is coming out of the generator is AC that is why it is known as AC generator now let me go to the principle of it the principle said that it works on the principle of electromagnetic induction where the magnetic flux through coil changes and induced current is produced so how does it happen it has been explained in the construction so in electric current generators what happens is you have magnetic pole and inside the magnetic pole the magnetic pole is fixed and inside the magnetic pole I mean in the space between the magnetic pole the coil is kept suppose the coil is named ABCD so what happens is I rotate the coil if I rotate the coil what will happen if I rotate the coil the magnetic field passing through the coils will keep on changing how it will keep on changing so magnitude remains the same but what about the direction of the magnetic field tell me suppose I have a coil here suppose I have a coil here and this is this I am rotating like this so it is kept between North Pole and South Pole and this is getting rotated so how it is getting rotated so try to understand this this this coil is coupled with a driver here which rotates it so this driver is rotated and as soon as this is rotated this coil is also rotated and once the coil is rotated there is a changing magnetic field through it and due to this change in magnetic field a current is generated in the coil which is received outside as the output current so this is what electric generator is so electric generator is a concept of electromagnetic induction so now I'm going to your book so your book tells that alternating current generator consists of rectangular coil ABCD called armature so what is armature armature is the coil rectangular coil which I am which we are using the armature coil consists of large number of tons of insulated copper wire won't over the soft iron the coil is kept between poles of strong magnets R1 and R2 are two slipperings connected to two ends of the coil and convey the current produced outside the circuit so see what I'm trying to explain is the same thing I have told you five minutes two minutes before that what happens the coil keeps on rotating and as soon as the coil will keep start rotating due to induced voltage difference induced current would be generated which would be received outside and that would be output of the AC generator now how does it work so working principle also I have explained it to you that working principle also have explained it to you so go to the other page the working principle has been given given to you so what happens on the other page on page number 30 it has been shown that between North Pole and South Pole two coils have been kept sorry a coil has been kept and coil is getting getting rotated and through brushes the current are coming outside so that is what the principle is now what do you mean by AC current so AC current means I discussed that in class in details now you understand that what difference between DC current and AC current is that DC current will never change its direction AC current will change in direction so that is why in your book it has been written written that AC current changes its direction 100 times in one second so the frequency becomes 1 by 100 in India so that's how it is and now application has been given one thing which is very important and is asked in the examination is difference or advantages of AC current over DC current so one thing which is how it is economical I'll explain you in details the second thing is the most important benefit of AC AC current or AC voltage is it can be a step down or a step up easily so I have already explained to you that the transmission of the power happens at very high voltage why it happens at very high voltage because we need to lower down the current why we need to lower down the current we need to lower down the current because I square R losses are there so when a current having when a current carrying conductor having current I is flown through it the power loss would be equivalent to I square R so more the current passing through a current carrying conductor more the power loss hence we need to reduce the amount of current through the transmission line to reduce the amount of current through transmission line we use transformers in some time I teach you transformers also that is also best on the principle of electromagnetic induction only so to reduce this I what I do is that so what happens in transformer try to understand transformer this side I give some input as I give input there is alternating current into it due to alternating current what happens on other side I have another coin as alternating current is flowing through this alternating current will produce varying magnetic field due to varying magnetic field it is as this varying magnetic field will cross cross sectional area of this coil as varying magnetic field is there a current would be established on this side this is the principle of transformer so what happens is that how many of you are there can you please give your attendance now because people are leaving then why do they tell me to conduct classes when they are not interested in it people who are there give your attendance quickly who is there who else is there Kirchana is there who else is there only two people I'm teaching now okay no issues just look at here then I'll explain you transformer first and then I go to advantages and disadvantages so look at here so transformer what happens have you guys studied transformers is it there in your syllabus let me just check yes it's there in your syllabus so let me teach you transformers and then I'll come come to so what happens in transformer is that here input coil is there or primary coil is there input coil is also known as primary coil why do I call it input coil because in input current suppose a current is coming from generator and I need to step down the current or I need to step up the voltage so the current which is coming suppose this is generator and from here from the brushes of generator I am feeding this current to the coils of the transformer and what happens this goes and this is AC current so on the other side of this we having secondary coils now why this is called secondary coils because try to understand this is core type transformer I have taken shell type transformer has been given in your book there is no difference in the construct the construction of the shell type is different the principle remains the same so try to understand what happens is whenever this current will go always remember this AC current so I have told you that magnetic field produced due to a current carrying conductor is this if this I is changing which is changing in AC current so this magnitude or the direction of the because I is changing in its direction in AC current what what is happens AC current is denoted like this I is equal to I not sine omega t plus phi so it means that this is a sine curve and what how the sine curve is sine curve is something like this so if if the current is sine curve it means that for some time it is positive and for some time it is negative what do I mean by positive and negative I mean by positive and negative what I mean by positive and negative is that sometimes it'll be flowing in this direction and and half of the time it'll be flowing in opposite direction as the direction of the current is changing what happens over here is the magnetic the direction of the magnetic field produced due to current in the primary coil will also be changing I mean you will have varying magnetic field over here the change in there would be change in the direction of the magnetic field as the direction of the magnetic field would be changing due to that a voltage would be developed across the two across the two terminals of the coil due to this induced voltage a current would be generated in this coil in the secondary coil and which would be collected by the other wires which is called the grid system so it will go to the grid is it okay so what happens over here is the fundamental of transformer is that there is one thing called transformer ratio what do I mean by transformer ratio transformer ratio is or you can say that it the power transferred from this side would be equal to power transferred on the other side and what is the power power is known as V into I so power may be on this side on this side input current I write VIII and output voltage I write VOIO so what happens here is VO or try to or let me write it like this VI by VO is equal to IO by II so you try to understand if VI is more it means that if input voltage is more then output current would be more because if here numerator is more here also numerator would be more if output voltage is more to keep this multiplication cons equal on both the side VO will reduce so if try to understand if voltage is VI here and VO here if VI is input voltage is greater than output voltage it called step down transformer what do I mean by step down transformer step down transformer means the no Kirken I I saw your message so doubt now the coils are of same material both the sides but the number of turns are not same in both the sides so what happens is there is another relationship which says that if N1 turns are here and I am sending a current I1 to primary coils and in secondary coil N2 coils are there N2 turns are there so N1 I1 will be equal to N2 I2 so what happens is I2 by I1 is equal to sorry this this I have written it wrong this would be I1 by N1 is equal to I2 by N2 so N2 by N1 is equal to I2 by I1 so what happens whichever side more turns would be there in the coil that side more current would be generated so in a step down transformer step down transformer means I am reducing the voltage reducing the voltage means to keep the power same I am increasing the current so what happens I increase the current increasing current means you should know that if you have to increase the current you have to keep more number of turns here so whichever side more number of turns are there that side more number of I mean more magnitude of the current would be established now in that particular scenario or in case of transformer look at here so what I told you initially is that generally here when the current comes from the generator I need to reduce the current on the other side on the secondary side so if I have to reduce the current it means that if N2 coils turns are here and N1 turns are here and current has to be lesser than this primary coil it means that N1 has to be greater than N2 if N1 is greater than N2 then I1 will be greater than I2 if I1 is greater than I2 as Vi has anti-proportional relation relationship V2 will be greater than V1 it means that output voltage will be greater than input voltage as output voltage is greater than input voltage this is called step up transformer so this is the principle of transformer now how does it happen now so I was on AC generator and AC dilemma or AC generator and I was telling you that why AC generator is better than DC generator so AC generator is better than DC generator because first thing I told you that they are stepping up or stepping down the voltage is easier in AC generator the second thing is the electric current can be transmitted to distance places without any significant line loss what happens in DC current as the current is never changing the losses are more in DC current the losses are very less in AC current so benefit of having AC generator over DC generator is it is economical stepping up and stepping down the voltage is easier and line losses what do you mean by line losses so wherever power is generated that point is called power station from power station that power is transmitted to different distribution houses now in the transmission of the power i square r losses are involved for AC current those i square r losses are lesser as compared to the DC current so these are the three main advantages of AC generator over DC generator disadvantages so disadvantage is one as it is always changing there is some peak voltage because it is sine value so you can understand that v is equal to v0 sine omega t I am writing as the value of omega t will keep on changing value of v will keep keep on changing so as soon as this becomes omega t becomes 90 degree v becomes its highest value v0 and suppose you touch or get a shock when v is equal to v0 it's very dangerous for you so peak voltage is dangerous in this case and there are different uses like they have given electro typing and electro defining and all those things so in that AC current cannot be used in that only DC current can be used so those things are very important okay so any other doubt that you guys have you can send me okay any other doubt that you guys have okay conversion of moving coil galvanometer to okay so i'm getting two three doubts one second just let me go through it okay let me just open that conversion page then i'll tell you so Ruhi try to understand you have asked a question that why AC losses are lesser than DC losses so AC losses or DC losses will all depend on the current now what happens in case of AC current I can step it down so I can bring it down to a level where it is optimum where I can afford that loss DC current I cannot whatever DC current I am producing the same has to be transmitted so suppose I am producing uh suppose 100 ampere AC current and 100 ampere DC current and both has to be transmitted 100 ampere DC current will have to be transmitted in form of 100 ampere 100 ampere AC current can be converted I mean can be stepped down with the help of step up volt step up transformer where I increase the voltage and take take the current down make it from 100 ampere to 10 ampere and and with the help of that 10 ampere current I transmitted so what happens is that as the transformers can be used in case of AC current I it is possible to bring down the current level in case of AC current as I bring down the current level in case of AC current it is possible for me to reduce I square R losses by reducing the value of I so I am not saying that you can directly compare AC current and DC DC current losses when the value of the current is same the loss would be same but as the value of the current can be reduced with with the help of external equipment which is known as transformer hence by reducing the current the losses can be manipulated that's what the answer would be for your question so now let me move to okay so let me move to changing of one second so go to the page number which page number it is all of you I'm just referring your book I will teach you from your book itself okay so what is an emitter emitter as I have already told you that it is a device to measure current in any circuit so what happens is how do you convert a galvanometer into an emitter so construction has been shown in in a particular in the particular diagram on page number 23 of your book what happens is the the construction is like this so you have a galvanometer you have a galvanometer so we have a galvanometer for our reference so here is our galvanometer a current is passing through it current I is passing through it now what I do is that I put a resistance in parallel with it and this particular diagram I'll explain how it is used so this is used as an emitter so what will happen is obviously there would be some resistance over here so the current would get divided into two parts of this circuit so suppose the current going over here is IZ and current in this particular part would be I minus IZ now see what happens so now listen to me how it happens so an emitter is connected in series with the element so that the current is to be measured actually passes through it so what happens you always see whenever I make a circuit what I do is that what I do is that I put an emitter in series with the circuit why I put emitter in series with the circuit because I have told you that series connection of any particular equipment means same current will pass through that particular thing so that is why it has been written in your book is that the emitter is connected in series with the element so that the current because whatever current I want to measure I want to measure it directly so it passes through passes through that in order to ensure that its insertion in the circuit does not change the current and emitter should have zero resistance so emitter is designed to have been very small effective resistance in fact an ideal emitter should have zero resistance an ordinary galvanometer instrument it gives full scale deflection with a small current of few micro mps to measure large current with it small resistances connected in parallel with the galvanometer coil why do we connect parallel see here I have used this galvanometer what will galvanometer do galvanometer will detect the current then why am I using this parallel parallel resistance with this so try to understand let me make parallel resistances like this so what happens suppose this is 2 ohm and this is 2 ohm so 2 ohm and 2 ohm if I find out the resistance of it 1 by r will be equal to 1 by 2 plus 1 by 2 how much it is it becomes 2 by 2 and 2 by 2 is equal to 1 by r is equal to 1 ohm so r is equal to how much as simple as that so this is how it is so this parallel current because the resistance over here has to be very very small if I take resistance of galvanometer suppose this is rg I want this this has been put in series I want this particular resistance to be very small suppose I suppose this resistance is not small how can I make this resistance very very small so put it in put a parallel resistance to it the combined resistance would be very very small and you can find out the value of resistance passing you can find out the value of current passing through it and and and and the current can be measured so that's what it has been written so conversion of galvanometer means you have to put it in the series with the in series with the current carrying conductor or in the circuit why it has to be put in series because in series the same current same current would be passing through it the second point that we need to take care of is that the resistance of the ideal emitter should be zero generally it is not zero so to make it zero what do we do we we shunt it so that is why it has been written in your book that resistance connected in this way is called a shunt only a small part part of total current passes through galvanometer and remaining current passes through shunt so in this way the current measuring happens over here so did you understand this concept yes or no tell me okay great fine so that is how that you can understand once again let me go to voltmeter now now voltmeter what will happen voltmeter would be connected in parallel because i want voltage to be same so voltmeter has to be connected in parallel but the current passing through that would should be very very less so what will i do i'll put a resistance in series that is why resistance in series why two things again two three things in common which i which i want here is how do i measure voltage by putting things in parallel so i put things in parallel how so i will put galvanometer in parallel to the points where i need to measure the voltage but galvanometer will have certain resistance i don't want small resistance here i will like to increase the resistance so that very small current is wasted due to connection of this galvanometer that is why with the resistance of this galvanometer i will put our resistance in series if i if these if resistance of galvanometer suppose this is rg and the series resistance which i'm putting with it suppose this is rs so what will happen in that particular case rg and rs they will combine together and increase the resistance of this path of the circuit as the resistance will increase very very less current would be passing through this galvanometer and that's how the voltage would be measured across it now tell me any doubt any doubt that you have okay fine so you guys are not saying so now what i'll do i have covered most of the portion of your book what i'll do is that i'll wait for your doubts if you have any doubt you can tell me i can take over those questions otherwise i'll wrap up the class am i getting any doubt okay who you are saying that with increase in rv across the galvanometer will also change no why will v across the galvanometer change i am saying that current is passing through it when the current is passing through it it'll deflect resistance has been put here resistance why resistance has been put here so that very amount of one thing for perhaps i forgot to tell you that galvanometer is very sensitive to even a small amount of current so why a galvanometer is used in place of ammeter because galvanometer can measure currents even in millimeters and and and something lesser than that that is why a very small amount of current is going through it and a very small amount of current will able to deflect the needle of the galvanometer and the current would be detected or the voltage would be detected so region behind putting this resistance is to increase the resistance in this path such that the circuit current is not affected that much if there is change in circuit current suppose the change is i or suppose 5 ampere current goes suppose i have let me remove it for you so suppose here i have put my galvanometer and i have put this resistance and i have to measure voltage between these two points a and b now suppose 5 ampere current is going here and if resistance is very small here what will happen suppose 2 ampere current goes here so in the circuit only 3 ampere current would be left out so here that the voltage v a b should be equal to or v b a should be equal to v a b should be equal to 5 ampere into resistance over here resistance between a b so 5 r a b now suppose 2 ampere goes here it it remains 3 r a b then when there would be change in or there would be error in the measurement of voltage to remove this 2 ampere or to reduce it to negligible level I will increase this resistance such that of small current goes over there so that this v a b would be this current which is 5 would be nearly equal to 5 into r a b so that's how this arrangement would be made are you understanding it okay fine any other doubt that you guys have asked me do you guys need any other class on sunday or perhaps any other date you can post it in the group okay nobody is asking me any doubt so perhaps i need to wrap it up any other doubt in this chapter or any other chapter please ask okay fine okay so i'm wrapping up the session now thank you so much for attending the class if you have doubt you can still ask me but i'm not getting any doubt so i've covered up the portion i needed to cover so thank you so much