Current Electricity Lecture Notes

hello children in today&#39;s class we are going to cover the entire chapter of current electricity so children once again let us think about this chapter so in this chapter we have three units in a unit a we will be covering about the concept of charge current potential resistance and ohms law of factors affecting the resistance finally choice of material means how we are going to choose a material for a uh different purpose okay fine whereas in a unit B we will talking about the EMF terminal voltage potential drop internal resistance and the combination of the resistors there only we will learn about the series and parall combination whereas in a unit c purely we&#39;ll be discussing about electrical energy electrical power and household consumption of electricity I mean how are we going to calculate the what we can say cost of electricity so generally we will be using a uh electricity right so how are you going to to pay money for that so that will be covered in a unit c children this chapter seems to be lengthy but in fact it is a easy one to understand if you can go step by step if you can go step by step definitely what happens this chapter is going to be very very easy in the previous classes we learned already the concept of charge so let us recall once again what happens when two non-conducting bodies are rubbed each other children one body will lose some charge where another body will gain some charge let us see one example so what happens when glass rod is rubbed with a silk cloth here in this process children glass rod will lose electron means there will be transformation of charge from glass rod to Silk cloth which means what here glass rod is losing some charge whereas silk cloth is gaining some charge due to which here glass will become positive chargeable whereas silk cloth is silk cloth will become negative chargeable one children what is the unit of charge here so the SI unit of charge is Kum so when you want to measure the less amount of charts we use mum which equal 10 powerus 3 Kum micrum which equal 10 - 6 Kum nanoc which equal 10^ - 9 Kum children then how can we determine the quantity of charge or what we can gain by an object it&#39;s very very important so if you want to know that first of all we should know what will be the charge of of electron so we all know very well that so the charge of electron is - 1.6 into 10 power - 19 kums so here the quantity of charge is determined by the number of electrons if more than number of electrons are there definitely charge will be more if the less if the less the number of electrons are there definitely the charge will be less on that particular body but how can we calculate the total amount of charge on the body for suppose children on one body only one electron will be there let us say for example then what will happen the charge of that body will be minus okay let us talk about the only magnitude 1.6 into 10^ - 19 kums if there are two electrons are there then two * of 1.6 into 10^ minus 19 three electrons are there three times four electrons are there four times if there are n number of electrons are there then how to calculate the total amount of charge so if there are any number of electron then the total charge Q is given by here Q is given by so plus or minus here n into e see here in some textbooks it will be given n into small q also so we can use small q or small e to represent the charge of the electron don&#39;t get confused so this is how we can calculate the total amount of charge actually total amount of charge then here one important point we need to understand so since that time we talking about the Kum so Kum is a charge but the question is that how children each and every electron has some charge right but how many electrons together can constitute a charge of 1 Kum this a very very very important examination point of view let us see here means for example to have q is equal to 1um charge here how many number of electrons should be there actually so e is equal to what here let us take 1.6 into 10 power -9 kums Kum Kum gets cancel here so n is = 1 by 1.6 into 10^ -19 so this will be n is equal to 6.25 into 10 power 18 electrons children you can imagine here means these many electrons together will constitute a charge of one Co so if I say that 1 Kum charge is going like this then you should imagine that 6 25 into 10 18 electrons are going try to understand so that much what we can say you can imagine you know the quantity of a chart it&#39;s very very very small and even electron is very very tiny so here 6.25 into 10^ 18 electrons will constitute a charge of 1 Kum is it clear just copy it and charge is a scalar quantity so in exam they might ask for one Mark is chart scalar Vector so obviously you can set the scalar only now children let us see a concept of current so first of all what is a current children here so current is actually general term actually what does it mean it means that something which is in flow so for example if water is in flow we can say water current actually if heat is in flow we can say it&#39;s a Heat current means whatever something if it is in flow means we can call it as actual current but what is electric current children if charges are in flow then we can say that it is a electric current actually in this chapter soall current electricity we&#39;ll be talking about the charges which are in completely motion only so here the current which means what you should understand whenever we say it&#39;s a current so you should think it as a electric current only so electric current what does it mean children here so the charges which are in motion will constitute electric current me how much amount of charge is going in a particular time only we can say it as a electric current for suppose children here for suppose here here is a conductor through which small charge Q is going in a small interval of time then how can we write here so current is written as charge per time so children it is for a very very very small actually when you go for higher class we can write DQ by DT actually but now it is not needed actually when you learn about the differentiation then you&#39;ll get that concept of what we what the importance of DQ and Delta Q all these things so now you can learn it is a IAL to Q BYT for suppose children here in this for example n number of charts are going n number of charges then what the total charge total charge will be n * of Q or you can also write n * of V nothing is wrong in it then what is the total current total current can be Q by T it is a q BYT or even you can write I is equal to n e by T so this is how we can calculate the total amount of current is it clear fine so what is the current the rate of flow of charge is called electric current children what are its SI units let us see here it&#39;s SI units so here we know that I is equal Q by T Q is measured in terms of Kum T is measured in terms of time sorry T is measured in terms of second so here current is measured in terms of Kum per second this Kum per second only we can call it as a ampere this one we can call ampere the symbol is capital A a small amount of current if you want to measure then we can use here milliamp which equal to 10^ - 3 amp whereas microamp which equal to 10 power - 6 aamp and even Nano a which equal to 10 power - 9 aamp is it clear fine then how can we measure the electric current children we measure the electric current by using a device called it is a ameter and the very important thing is that ameter is always connected in series so it is always Con in the series that&#39;s fine and here you make get one out so here sir what actually ampere so how can we Define ampere examination point of view this defin is very important for suppose children here is here if charge of one Kum is Flowing if charge of 1um is flowing in a 1 second time means here if one Kum charge Flows In know 1 second of time through that area of crosssection of the conductor then we can say that the current is equal to to the 1 ampere but how does the current flow is a important question children here how does a current flow so here current always flows from high potential very very very important high potential to current always flows from high potential to low potential so here we are getting a one more word called potential is it clear fine now we will see what is the potential and how can we measure the potential and and what are its units just copy this so that we move to the potential and as like a charge even electric current also scalar quantity only now we see what actually potential and what is the potential difference also for suppose let us say here is some electric field let us say here is some electric field just think here is electric field somewhere one charge is there children here so what type of charge charge it is it is children it is unit positive charge unit positive charge actually it&#39;s this also we can call a test charge it is also called a test charge actually it is not available only in assumptions only it is a possible what is the test charge children the charge which is influenced by other charge but which cannot influence other charge so it is highly impossible only here is a theoretical purpose concept purpose assumption purpose only it is a possible okay for suppose children this charge is placed at a infinite distance children let us suppose here now what is our task we have to bring this unit positive charge from where from Infinity to a point in a electric field children don&#39;t you think see in our in general also if you want to move anything from one point to another Point children definitely some work is done obviously yes sir yes now don&#39;t you think that for this process in this process some work is done yes for what work is done is a question here to move a charge what type of charge unit POS chge from where from Infinity so children here the amount of work done the amount of work done to move this unit POS charge from Infinity to a point in electric field is called electric potential so electric potential is nothing but what children it is nothing but the work done to move unit postive charge from Infinity if W is a work done and Q is a charge then mathematically electric potential is defined as work done by charge work done by charge if you know the potential if you know the charge how can we calculate the work done obviously W is equal to V * of Q we can use is it clear fine and what s unit children yes here W is measured in a JS charge is measured in a Kum so here J per Kum it is also called as it is also called as volt V LT children we know very well that whenever we are writing a units make sure that first letter should be a small one it should be a small letter is it clear so here the s unit of electric potential is Vol but how can we measure the potential by using a device called what Vol meter by using device called Old meter that is fine then what is potential difference children children here as like a charge electric current potential also scalar quantity only okay now we see the potential difference potential difference small difference will be there between potential and potential difference for suppose here here is a point a point a and here is point B let us see that here so here we can see that now the potential difference between these two points is equalent to the work done by charge then you make get a one out so what is the difference between the different definitions of potential and potential difference very simple so to define the potential we are assuming charged infinite distance but whereas here for potential difference the distance between these two points well defined so let us recall once again what is electric potential the amount of work done to bring unit positive charge from Infinity yes or no yes now what is the potential difference the amount of work done to move a unit POS from one point to another Point within the circuit is called potential difference is that clear fine so for this also units are same that is J per Kum simply we can say the Vol is a old so when you can say that the potential difference between two points is equal to 1 volt it&#39;s very simple when you can see that if one J work is done to move one Kum charge then we can say that the potential difference between these two points is equal to the 1 volt and here also we use a device so called what is that Vol meter very very very important so here volmeter is a device which is used to measure the potential difference between the two points and here voltmeter is always connected in parallel voltmeter is always connected in parallel is it clear children fine so this is a concept of potential and potential difference now we come to the concept resistance here children what is the resistance the term itself will give you a meaning resist means what stop resist means what stop means who is stopping here material who is stopped charges very simple charges in the sense electrons means whenever the electrons are moving through a conductor there will be some abstraction given to the flow of charges by the material this abstraction given only we can call it as a resistance then you may get one out so what is the reason for this abstractions that yes so if you can see the material children so in that positive Char also will be there but do you think that practically positive charges will move no they won&#39;t move actually so they&#39;ll be uh mean they&#39;ll stick to particular places but whereas when these electrons are moving then what will happen you know they may have collisions with the charges I mean positive charges even they have collisions among themselves also is it clear fine so the very very very very important thing is that here children so what is the resistance here what is the resistance children here the abstraction given to the flow of charges by the material by the material is called resistance here okay fine so what is the s unit of resistance so resistance is measured in ohm in ohm so the symbol we can write like this here is a oh we can write but here the very important thing is that children what is the reason children so here what are the reasons for resistance why electrons are given some what we can say resistance the first thing is that here collisions so here collisions between collisions between electron and positive charge electron and positive charge and what is the second reason children it collisions among the electrons collisions among the electrons collisions among the electrons so these are the two reasons in examp they&#39;ll ask you just you can write directly these two reason is it clear fine and here children the very important thing what is that here on which factors does the resistance depend examination point of view this concept is very very very very so here distance mainly depends on four factors here so the first one is it depends on nature of the material nature of the material nature of the material I mean what here different materials will offer different resistance if you can take aluminium copper children both might be a conductor but still they also offer resistance and that two they are differ because their nature is different and whereas the second one is that temperature this is very very very very important so here resistance also depends on temperature here we need to learn an important point so in the case of a conductor children in the case of a conductors here resistance is proportional to the temperature as temperature is increased definitely resistance of that conductor increases but whereas in the case of semiconductors in the case of semic conductor resistance is inversely proportional to the temperature which means what if you can increase the temperature the resistance of a semiconductors decreases clear fine and here third one is length children here so Here length of the conductor Here length of the conductor or length of the material whatever it may length of the conductor mean as length of the conductor increases practically it has been proved that even resistance also increases but what is the reason as length increases so they will undergo Collision for a long time so due to that what will happen resistance is increased so here resistance is proportional to the length so this also can be written to compare the resistance of the two materials if their lengths are given but make sure that they must be made up of with the uh same material okay fine and the fourth one is area of cross-section area of crosssection area of cross-section so experimentally it has been proved that here resistance is inversely proportional to area of cross-section so even area of cross-section for a conductor I mean you know it&#39;s a thin wire so wire can be written as children here of course area of crosssection of a thin wire can be written as &lt; r² so even we also can write R is inversely proportional to the r² so from this I can write here R1 by R2 is = to A2 by A1 so from this we can write it as a R1 by R2 is equal to R2 s by R1 squ you don&#39;t get confused here capital r is a resistance of the material R is a radius of the wire actually is it clear fine children so these are the factors on which resistance of a material depends is it clear fine children now here only we need to learn one more thing what is that here conductance we need to learn about the conductance so what is the conductance children here so we can rep with the G in some textbooks it can be even with the c letter also it is nothing is wrong but you have to mention what is that particular symbol so what is the conductance children here the reciprocal of resistance is called conductance so here the reciprocal of resistance is called conductance and its units are its units are so reciprocal right it is a 1 by ohm or we also can addite ohm inverse or we also can addite more MH or we can write as a cmen of course now we are not using these units but this unit we are using actually of course these four are the units for conductors excuse me so these four are the units of conductance only children what is the conductance the reciprocal of resistance is called conductance so its units are semen clear fine so now children so here we have two conclusions R is proportional to L and R is inversely proportional to a so from here from these two conclusions now we are going to get a One More Concept so now we will see what is a resistivity soal specific resistance soal specific resistance so here we got R is proportional to L and R is inversely proportional to 1 by a so from this two we can write R is proportional to L by a children here here is a proportional symbol is there can we repl by a constant so we can add here R = row into L by a children this is general formula to calculate the resistance of a material if its length and area of cross-section is no know but here the point is that what is this row is called so this row only we can call it as a resistivity resistivity resistivity or specific resistance specific resistance specific resistance specific resistance and here it&#39;s very very very important it depends on only two factors children it depends on only two factors what is that it depends on nature of the material it depends on nature of the material and it depends on the temperature it depends on the temperature and one more one more very important thing is that it does not depend on the what we can say length and area of cross-section which means what for example 1 M length copper wire 100 m length copper wire both specific resistance is same that is one is to one only why that&#39;s what I tell you it is a what we can say characteristic properties of M characteristic property of a material so it remains same for a same material children though means though you can change its length though you can change it area of cross-section the resistivity doesn&#39;t depend the resistivity depends purely on nature of the material and the temperature Clear fine and what are it units so let us see the units of resistivity units of resistivity so let us rewrite the formula for resistivity this can be written as R into a by L so your resistance units of resistance is what ohm okay area of crosssection M square and length is meter meter meter can so finally the units of resitivity are ohm met so these are the units of resistivity units of resistivity but how to define resistivity how to define resistivity so look at here if if a is = 1 M squ and L is = 1 M then mathematically row is is equal to the r only which means what here resistivity is nothing but the resistance of the material whose dimensions are unit I mean what whose area of cross-section and length are one unit is it clear so this what actually resistivity and the resistivity formula resistiv units and factors on which it depends children I I&#39;m telling you on which factor does not depend also very important it it doesn&#39;t depend on the length it doesn&#39;t depend on the area of cross-section it only depends on nature of the material and temperature is it clear so how to define resistivity children resistivity is nothing but the resistance of the material whose area of cross-section and length are one unit clear fine now here what is conductivity what is conductivity so conductivity symbol is Sigma so what is a conductance children conductance is a reciprocal of resistance similarly similarly conductivity is a reciprocal of the resistivity conductivity is the reciprocal of the resistivity and what are it units children here it is 1 by oh met or we also can write Cen Cen meter inverse so this is a concept of resistivity and condu just copy it now we discuss about the ohms law children what is ohms law actually for what it is actually children so ohms law will give the relation between amount of current which is passing through the circuit to the potential difference across across a conductor I mean to say that here means it is stated in 1826 so examination point of view it&#39;s a statement condition circuit diagram is important let us see a circuit diagram first so that you will understand very easily this is how actually the circuit diagram so here is plus minus and here is a battery this is key here is a resistor here your start so when key is on so there will be a flow of current there will be flow of current children here two points see examination point of view sometime they might give this circuit diagram they ask you to find the what we can say errors in that circuit diagram so mostly you know where there will be a question you know in the place of voltmeter they might give ammeter in the place of ammeter they might give voltmeter children always remember that old meter must be connected parallel ameter must be connected in a series so examination point of this circuit diagram is very important okay fine so what does OHS SL State children so OHS SL state that the amount of current which is flowing through the conductor or a resistor is directly proportional to the potential difference across it ends across dense is it clear fine so this can be written as here so here V by I is equal to constant experimentally it has been proved again I&#39;m telling you experimentally it has been proved this constant only we can call it as a r that is a resistance again I&#39;m telling you for a what we can say at a given temperature we are talking for a given material for a given length for a given area of crosssection the ratio of V by I remains constant so this can be written as V isal to I this is a mathematical form of ohms law V is equal I is a mathematical form of ohms law so what does it State children so OHS states that the amount of current which is flowing through the conductor is directly proportional to the potential difference what we appli across it ends but what are the conditions here so physical condition should remain same I mean what temperature pressure must be same then only what happens this ohms law is valid so in examination point of view even they may ask you about the condition also when this HS law is valid so you have to write that yes when temperature and pressure that the physical and physical conditions remain same then only it is applicable fine okay so based on oh children here so resistor soal conductors you see don&#39;t get confused you may get one sir resistor is different conductor is different why are you using children each each and every conductor offers some resistance don&#39;t again I&#39;m telling you so you we do not have a conductors with a zero resistance any conductor offers even at least some resistance is it clear so if I use conductor resistor don&#39;t get confused okay fine so based on the H SL children here we have two types of resistors one is omic resistors another one is non ohic resistors so first we will see omic resistors or we can call omic conductors also nothing is wrong omic conductors so what are omic conductors children so the resistors are the conductors which obey which obey ohms law which obey Oh&#39;s law are called omic resistors or omic conductors and children so in this case children for the very very important that in the case of omic resat the relation between potential difference and current is a linear that&#39;s what these resistors are also called as linear resistors linear resistors linear resistors then how the VA graph and IV graph will be there for omic resistors we&#39;ll see so this examination point of very very important so it is a I here is V children so we get a straight line which is passing through the origin so what is the slope of V gra will give you so here slope of V graph that is what y components by X components that is V by I is nothing but what children resistance children examination point of VI it&#39;s a very very important but here only there will be a confusion let me tell you so this is about the VA graph but if you can make a IV graph if you can make a IV graph so this is VA graph now let us make it the IV graph i v graph so here for same values this will be V here is I so still you get a straight line passing through the origin so for this slope slope of IV graph slope of IV graph will be y components that is I by V children V by I is equal R but I by V is equal 1 by R 1 by R is nothing but what conductance conductance so here don&#39;t get confused here so in exam they ask a question what is the slope of va graph VA graph will slope of V gra will give you resistance but whereas the slope of IV graph will give you conductance so this is what actually the clarity we should have okay fine so what are the examples for om almost all All Metals All Metals comes under omic resistance is it fine okay now we see hope it is Cy children take this fine now nonic resistors children let us see nonic resistors non omic resistors so you can guess which do not obey which do not obey ohms law which do not obey ohms law and children here in the case of nonic conductors as they are not obeying the ohms law so the relation between the potential difference current won&#39;t be linear it is nonlinear that&#39;s what the resistors also called as nonlinear nonlinear resistors nonlinear resistors so examples for this lead and filament of bulb filament of bulb even diodes even transistors all semiconducting materials will come under this nonic resistors now how the vi graph will be there for this VI graph children very very important so it is like this nonlinear and one more thing is that it is not compuls that this graph should start from the origin it may or may not it is so what is the slope Children Here slope of VI graph of the nonlinear Condor so as a nonlinear direct you cannot take a v value and I value we can take only change in what we can say potential by changing current that is here Delta V by Delta I so Delta V by Delta I will be Delta R it is nothing what dynamic resistance Dynamic resistance Dynamic resistance means what it will vary children dynamic means what it&#39;s not a constant so it will be changing is it clear fine so this is about ohms law and omic resistors and even nonic resistors just you can copy now we see the choice of material yes children now we&#39;ll see the choice of material children depends on the purpose we are going to pick up so depends on the purpose so we need to pick up the material with the different properties actually so here first for suppose children if you are using for a correcting purpose for suppose here uh for suppose here electrical connections electrical connection so usually we can prefer either copper or aluminium but what should be the properties of this electrical connection children so here these wires whatever we are going to pick up the material I me to say that so they should have low resistance and high melting point they should not melt easily is it clear fine and here the second one is standard standard resistors which we&#39;ll be using in a laboratory purpose actually so here the very important they should have high resistance High Resistance and they should not depend on they should not depend on temperature I mean the resistance should not vary with the temperature and here the examples are very important examination point of view it is mangine it is mangine even constant constant t or the examples for standard resistors and here third one is fuse one wire children fuse fuse wire about this so we&#39;ll be discussed in household circuits in detail actually so fuse wire the very important thing is that here fuse wire should have high resistance High Resistance but low melting point and your fuse is made up of with a lead and Tin lead and clear fine and the next one is so it&#39;s a fuse wire and let a filament wire children it is filament so for a filament purpose generally we use tungsten right we use tone so what should be the property children it should have high resistance and high melting point both should be high only both should be high only now heating element children heating element I mean generally we&#39;ll be using for a water heaters right example I&#39;m telling you so made up of with a nicrome made up of with the nicrome and what&#39;s the properties here so eating hel that particular material should have high resistance High Resistance and high melting point high melting point is it clear so these are the first we should know the properties of that particular material based on that only we can pick up we can pick up for what we are going to use Clear fine last point in this unit I can say so as we discussing actually you know one sh video I cannot say last topic and all this but as I said that so unit wise you can go preparation so after unit wise preparation you can go for a one short revisions all the things okay okay so in this I&#39;m talking about the super conductor and super conductivity children this are very very very very important super super conductor super conductor children in the case of conductors we know that here resistance is proportional to the temperature I mean what if you can increase the temperature resistance also increases okay that is fun but what happens when we decrease the temperature children yes so when we decrease the temperature children obviously resistance must be decreased so if you go on De the temperature to very very very low and the resistance goes on decreasing decreasing decreasing and at a very very very particular low temperature it has to be zero is it clear means at very very low temperature very very very low temperature what happen the resistance of the conductor is zero where the conductivity will become Infinity the conductivity will become Infinity is it clear that conductor in that position we can say super conductor means the conductor with zero resistance at a very very very low temperature is called super conductor this phenomena is called super conductivity example Mercury so Mercury can behave like a super conductor below 4.2 Kelvin So Below 4.2 Kelvin here super what Mercury behaves like a super conductor children super conductor means what here The Temper very low temperature resistance will be zero resistance will be zero means what conduct ity must be a Infinity okay just copy this fine so children now we discuss what is the electromotive force what is a terminal voltage what is the potential drop what is the resistance and how they are related children examination point of view this is very important even we can expect the numericals based on this also okay now fine so now let us see children so first if you want to know that first we should know what actually electric cell is so let us make electric cell first and here is negative terminal children we know very well that actually so here what we can say electric cell which maintains the constant potential difference between two conductors by a chemical reaction to obtain a constant flow of current and what kind of energy mean there will be a you know what we can say transformation of energy right so here electric cell which converts the chemical energy into electric energy the symbol is what children so the symbol of cell will be like this minus and a plus is it clear fine now let us see children do you think is a closed circuit or open circuit obviously a closed so it&#39;s a open circuit it&#39;s not a closed circuit because here no resor is connected right it is purely purely open circuit means whenever we bring a new electric cell yes this is its position so electric if you can see electric cell CH on that something is written in terms of volt that is nothing but actually what we can say it&#39;s a EMF electromotive force electromotive force can means we have two types of definition it can be defined in terms of work done also so how can we Define a work done so before that children first we&#39;ll discuss in terms of potential difference children here is a open circuit right here so here the potential difference across the open circuit only we can call the EMF so simply what is EMF Children Here EMF is nothing but the potential difference between the terminals of a cell in a open case means in open case in open circuit in the case of open circuit the potential difference between these two terminals is nothing but the EMF but it also can be what we can say different in terms of work done for suppose one charge is there here so to move this charge in entire circuit entire circuit children so work must be done that is what socaled total work done so the total work done to move a charge in entire circuit is called as electromotive force or electromotive force is nothing but the potential difference across the open circuit that&#39;s it across the terminals of the cell in an open circuit in an open circuit so here EMF simply I can write here electr motive force can be written as total work done by charge total work done by charge so it is also so what we can say J perum so it also can be measured volt only okay and which factors this EMF depends children so here EMF depends on mainly two factors EMF depends on two factors one is nature of the electrolyte nature of the electrodes let us say first nature of the electrodes what type of electrodes are we using their nature and the second one it also depends on the nature of the electrolyte nature of the electrolyte and children it does not depend on few Factor it does not it does not depend on the following factors on which factors for suppose it doesn&#39;t depend on the size of the electrod children size of the electrodes it does not depends on the size of the electrodes and also depends on the distance between the electrodes distance between the electrodes and also it also what does it depend on the amount of an electrolyte amount amount of an electrolyte Electro light is it clear so this is about actually electromotive Force I&#39;m telling you what is Electro motive Force here what is electromotive force the total work done to move a unit posi charge in entire circuit I mean inside and outside inside and outside I&#39;m telling you is called electromotive force or electromotive Force simply we can Define as a potential difference between the terminals of a cell in a open circuit is called electromotive Force so it depends on nature of the electrodes and nature of the elect it does not depend on the size of the electrodes distance between the electrodes and the amount of an electrolyte clear fine now we see what is a terminal voltage what is terminal voltage now children here so now so far it is in open circuit let us connect children here now okay now we are going to connect to a one resistor let us say it is current to the resistor okay then what happen happens current starts flowing current start flowing now don&#39;t you think that it is in a closed circuit yes so here terminal voltage terminal voltage so usually children terminal voltage we represent with a V so what is the terminal voltage terminal voltage also can be can have two definitions children here so what is the first simple definition terminal voltage is defined as a potential difference between the terminals of the cell in a closed circuit whereas EMF is in open circuit whereas the terminal voltage let us recall once again what the terminal voltage it is the potential difference between the terminals of the cell in a closed circuit is called terminal voltage another way also we can Define children this is completely outside of the cell we can say external this is internal so from let us say Point uh let us say Point C Point D so here to here to move move a charge some work must be done yes or no so the amount of work done to move a charge in an external circuit or outside of the cell is called terminal voltage so this I can Define as a small W by Q so for this also units are Vol only for this also Vol only clear fine now we discuss about the potential drop potential potential drop Will rep the small V what the potential drop okay so terminal voltage nothing but what work done in in what we can out what in exal circuit out the cell but don&#39;t you think that inside also charge has to be moved yes for that also for that some work must be done that work done only we can call as a potential drop I mean what here potential drop is a work done to move the charge within the cell children within the cell so we can the w- by Q for this also un needs volt only children now if you can see here if you can see here electromotive Force terminal voltage potential D these three are work done only three what makes the difference here so here children w- by Q is a work done to move charge within the cell whereas W small W by Q is a work done what we can say to move the charge exteral circuit if you can add these two what you&#39;ll get here total work done to move the charge total work done to move the charge entire circuit this outside of the circuit is the inside of the circuit this is what total circuit this is so this is nothing but what actually EMF so it is EMF is equal to this what potential what we the terminal voltage plus this is what potential drop children this is a very very very very very important def important relation it is okay fine children now again I&#39;m telling you whenever you want to calculate whenever you want to calculate what get the terminal voltage you only consider external resistance so how to calculate this terminal voltage terminal voltage is equal to Total current in the circuit into external resistance only external resistance only but to calculate the potential drop you need to multiply total current into internal resistance we&#39;ll discuss internal resistance don&#39;t worry about it okay now try to understand so if you want to calculate about the if you want to calculate the terminal voltage total current into external resistance if you want to calc the potential drop total current into internal resistance now you substitute here you&#39;ll get here i r + i r here you can take I into r + r is equal to EMF so this is EMF is equal to if you want to Cal the current it is is EMF by total resistance that is internal resistance and external resistance so this is how we can calculate the total current in the circuit if if resistance and EMF is known is it clear just copy it now we discuss about the internal resistance we discuss about the internal resistance fine can this yes CH what is the internal resistance children inside of the cell what will be there electrolyte will be there it might be the conducting material but as I told you earlier even copper and aluminum might best best conductors still they offer some resistance similarly here this electrolyte also offers some resistance so the resistance offered by an electrolyte within the cell is called internal resistance is called internal resistance so examination point of view also this a very very very important internal resistance children purely it is offered by electrolyte only electrolyte so the resistance given by an electrolyte within the cell is called internal resistance will repes with a small letter children this internal resistance depends on intern resistance depends on first one surface area surface area of electrodes children so here inter resistance is inversely proportional to the surface area of the electrode and the second one is distance between distance between the two electrodes children distance between the two electrodes so here in resistance is proportional to the distance between the two electrodes whereas the third one is temperature so experimentally it has been proved that here inter resistance is inversely proportional to the temperature so fourth one is concentration of an electrolyte concentration children higher the concentration of electroly higher is a internal resistance is it clear so there are the four factors surface area of the electrodes distance between the electrodes and temperature of an electrolyte temperature of what electrolyte and the concentration of okay so concentration of an electrolyte so there are the four factors on which internal resistance depends fine children here then how EMF uh internal resistance external res terminal voltage or related is very important based on this we have numericals ch here so interal resistance is equal to we can write as a ex resistance into EMF by terminal voltage minus one children based on this we have a numerical children it is most most most most wanted for examination point of view usually we are getting a numericals even in Bard also so here small R is equal to see children what is the capital r external resistance small R is what here internal resistance it is a EMF and terminal voltage children once again let us recall what is the difference between EMF and terminal voltage what is EMF children here the potential what we can say difference between the terminals of the cell in an open circuit what is the terminal voltage here the potential difference between the terminals of the cell in a closed circuit is called terminal voltage is it clear fine now children here we have combination of resistors so here under this combination of resistor children we have two types of combinations first one is series combination second one is parall combination first let us see series combination series combination here so see children here first when we can say that resistors are con Series so to make the situation simple just will consider only two resistors so let us see two resistors its resistance is R1 and its resistance is R2 So This Is How They are connected in the circuit plus minus the potential uh difference between the cell is let it offers V let us say that here so now when you can say that two resistors are in series when you can switch on this so the current should pass like this same current I same current I so two resistors are set to be in series if same amount of current can pass through that resistors it might be two or 100 res if same amount of current is pass through 100 resistors then you can say those 100 resistors are in parallel okay so the first condition is what here current must be same current must be same through all resistors whereas here potential difference is divided very very very potential difference is divide among the resistors for example V is the total potential difference let us see that across this it is V1 across this it is a V2 which means what here in a series connection current is a constant but potential difference is divided among the resistors connected and the total potential difference can be written as in this case V1 + V2 if more number of resistors are connected V1 plus V2 plus V3 plus blah blah blah like that it can be okay now is it clear fine then how to calculate the total resistance if two resistance are connected children the effective resistance in a series connection is equal to the sum of the resistance of the individual resistors individual if more number of resistors connected so what we have to write we have to write as a R1 + R2 + r 3+ so on plus rn rn for suppose children all these resistance all these resistors have equal resistance then r s is equal to n * of R this is how we can calculate the total resistance that is fine but here examination point of view if two resistors are connected like this they might ask calculate the potential difference across R1 across R2 so across R1 we can write like this V1 is equal to very important I into R1 by R1 + R2 whereas to calculate vs2 V2 is equal I into R2 by it is R1 + R2 so these two formulas are very important to calculate the potential difference across the individual resistors across the individual res so children here so what I this is a conclusion actually so the the total resistance is always greater than that of the resistor with the maximum value in that combination so how to calculate here just you can add resistance of all resistors then you&#39;ll get the resultant resistance clear fine now we discuss the parallel comination we discuss the par children in a series combination two points are very important what is that current must be same through all resistors whereas potential is divided now the second combination is parallel so second combination is parallel so how the connection will be again I&#39;m telling children so we are considering only two res if you want you can take more than two also no one will question you okay so it is R1 and here is R2 so common points okay here is B sorry key key and cell getting battery nothing is wrong plus minus now if you can switch on this what happens current start flowing but here there are two paths are there so definitely what will happen current will get divided among the resistor but how if more resistance is there less current will pass less resistance is there more current will pass in that manner the current will get divided okay so the first important point of this is that here the potential difference is constant across all resistance con to parallel whatever the potential difference will be there same will be there here same will be there here but what makes the difference here current is divided here current is divided among the resistors current is divided among the resistors such way that the total current is equal to the currents which are passing through the individual resistors the current which is passing through the if you can add all those current then you&#39;ll get the total current clear fine and how to calculate the effective resistance if two resistors are ConEd parallel children here the the reciprocal of resultant resistance is equal to the sum of the reciprocals of the individual resistances children very very very 1 by RP is equal to 1 by R1 + 1 by R2 if more number of res are connected plus + 1 by rn rn if all resistors have equal resistances equal resistance are then how do calculate the resultant resistance resultant resistance RP is equal to R by n RP is equal to R by n is it clear fine uh here examination point of children here here I told you that here current will get divided but how to calculate the current which is passing through the resor one and resor 2 very important so it is i1 is equal to so total potential is a constant anyhow that we know very well that is here is R2 by here R1 + R2 R1 + R2 whereas for I2 which is equal to V into it is uh not sorry it is total current I should be there right okay I by R1 + R2 so this is how we can calculate the total amount of current I mean the currents which are passing through the individual resistors examination point of view numericals can be as based on this okay just copy it okay now we discuss the electrical energy children let us recall once again law of conservation of energy so what does law of conservation of energy St children so according to law of conservation some energy energy neither be created nor be destroyed but it can be transferred from one form to another form children electrical energy is the most desired form of energy for suppose you can take electrical bulb what will happen electrical energy is converted into light energy some part even heat energy also if you can take a fan electrical energy to mechanical energy if you can take electrical heater electrical energy to what heat energy in fact children we cannot imagine modern world without electricon energy is it clear so is that means electric energ is that much important so it&#39;s very it&#39;s a responsibility to know what act electric energy and how it can be calculated I mean right fine so let us take a simple circuit to understand this let us say here is resistor with a resistance R and Pro with the cell which offers potential difference of v and let say key okay so when key is on what happens so current starts flowing so children already we discussed about the potential what is the potential if current is passing means what charge is moving as charge is moving means what here some amount of work is done so that amount of work done only we can call it as a potential difference how it can be defined children so your potential difference is defined as work done by charge from here only we can call it as W is equal to VQ don&#39;t get confuse here the work done is equal to the electrical energy so now on words we are going to use electrical energy I mean symbol as a w only don&#39;t get confused so here is a electrical energy so this is the first Formula to calculate electric energy if you know the potential difference and if you know the charge and children we know that here okay let us see second one second form of electric energy we know that V is equal to or okay we know that here I is equal to Q BYT from this children Q is equal we can it now here you can substitute here so then you get W is equal to v i or v i t sorry V it t so this a first Formula and is a second formula okay fine and children from the OHS law we know that V is equal I right V is equal I now you substitute V is equal R in this place so then what you&#39;ll get W is equal here it is I S RT i s RT is a one more formula you calculate the electrical energy now children so from this ohms law only V is equal I that is fine only but from this can we write I is equal VR yes we can write this you can substitute in this place you get W is equal that is v² by r² into R into T r² cancel so here is w Is = v² by R into T children these all are the formulas to calculate the electrical energy you make it one doubt actually so which formula I should remember or I should use is not like that we should remember and we should use so we have to use a formula to carry electrical energy based on the data given in the numerical is it clear fine and what are the units of electrical children yes obviously the S units are Js only obviously JS only is itally fine so before going to discuss about the commercial units of electrical energy we need to learn about the electrical power is it clear fine Children See don&#39;t get a power confusion with power children why means in the 10th class especially we have power in mechanics you know work power energy there we discuss about power whereas even we discussed in a lenses power of a lens different okay and here is electrical power don&#39;t get confused don&#39;t get confused still generally what is the power in terms of mechanics also the rate of doing work the rate of doing work is called power but here how to define at what rate electric energy supplied by The Source or at what rate electric electric energy is consumed by the resistor is called actually power so simply we can see that here power is equal to Children power is equal to electrical energy electrical energy by time electrical energy by time so in the simple terms power is equal to we can write it as a W by T okay this is a direct formula you can use okay so don&#39;t get confused here we have a few you know Expressions to car electric energy so let us recall once again W is equal to v i t w is = i² RT uh W is equal to what we got here v² by R into t means in each case if if it is div with the time time time time if divide with the time divide with the time divide with the time what you&#39;ll get electrical power the simple Lo logic logically think if you can remove time term then you&#39;ll get the electrical power simple so here second expression because it is by time right div with the time what you&#39;ll get here power is equal to VI I third one so here Al if you can divide with the time what you get power is equal to i s r fourth one if you divide with the time what you get here power is equal to v² by R so these are the Expressions to calculate the power so what are the units of power children yes uh it is measured in a watt so if huge power if you want to measure you can use here kilowatt or megawatt or it&#39;s a gig kilowatt is very very important here please remember this kilowatt fine okay now we see the commercial units of electrical energy commercial units of electrical energy commercial very important examination point of view commercial units of commercial units of electrical energy children we know that actually power is equal to work by time right okay sorry it&#39;s not work by time electrical energy by time so then electrical energy can we write as a power into time yes now power is measured in a what time is measured in a second so what into second can be a unit of electrical energy but the thing is that here so measuring what electrical energy in 1 second time it will be very less for example what is energy consumed with the refrigerant in 1 second can you pay electric bill for that 1 second no it is not at least for one month means what at least we need to measure time in terms of hours at least you should measure 1 Hour 2 Hour 3 hour that&#39;s what you know so time in the place of second we can take as a hour is that clear so here wat hour I telling you if power is measured in wat then wat hour is a commercial of electric energy if power is measured in terms of kilowatt then kilowatt hour exactly fine then wat hour is equal see in examination point of view how wat hour and kilowatt are related to the Jou they will ask you children 1 wat hour is equal to 3,600 JS whereas 1 kilowatt hour is equal to 1 Kow 3.6 into 10^ 6 J children this is actually commercial unit of electric energy this only we can call the unit so whenever we are talking about the electricity build children we will talk right how many units have we what we consumed 50 units 100 units so so one unit means what here 1 kilowatt hour if we have consumed 10 units 10 times of this much 100 units 100 times of This Much okay now so here kilowatt hour is a commercial unit of electrical energy is it clear fine and now we will uh talk about the power rating children so what is the importance of power rating if you know the power rating what benefits are we going to get what information are we going to have children whenever you can see whenever you want to purchase actually electric appliances we must see the power ratings actually so something is written for suppose example it will be written like this 100 W example I&#39;m telling you 100 wat and 220 volt so like this it is written so this actually power rating by knowing the power rating what information do we get so children first of all we will come to know about the resistance of that particular uh what electric appliance when it is in use how let us see here so from this power is given here 100 wat okay and the potential difference is 220 volt 220 volt so we know that actual power is equal to v² by R so from this here R is equal v² by P so R is = 220 into into 220 by it is 100 so R is equal to 484 ohm so this much amount of resistance that particular Appliance will offer if its power rating is this much Clear fine and what is the second benefit we are going to get so we will come to know about the safe limit of current Ching what is that safe limit of current means what maximum current can pass through through that particular Electric Appliance if if current will exceeds what will happen that particular Appliance will get fused okay fine so we know that P is equal V into I so I is equal it is a p by V so here you can substitute the values so this will be p is equal to how much 100 by 220 if you can substitute 0.454 approximately 0.5 aamp which means What that particular Appliance with this much power rating uh can bear only up to this much this a limit of the current what happens if current exceeds this as I told that it will get fused so this what actually information we have by what we can if you know the power rating of an electric appliance okay just copy it now we see how to calculate the cost of electrical energy consumed children here as we as we discuss discussed earlier what actually commercial units of electrical energy means whatever the electrical energy which we are using children that can be measured in terms of kilowatt hour soall unit is it clear so one unit means what 1 kilowatt hour 2 units means what 2 kilowatt hour so how to calculate the first of all electrical energy children here so electrical energy electrical energy so as I told you that it must be measured in terms of kilow hour only kilowatt hour only so for this you should know the power of electric appliance power must be kilowatt only and how many hours we are using that electrical appearance so if you know the power and if you know how much time it is used then you multiply you&#39;ll get the electrical energy simple it is but sometimes power may not be even given kilowatt then what we have to do here so here for suppose here power is given only in terms of what but here time is given in terms of hour okay then you must divide with th000 then you get it sometimes power might not be knowing you might be knowing about the potential difference in current still we will we will why we know p is equal VI I so then so either formula you can use to calculate electrical energy okay once electrical energy is done then what we have to do yes cost of electrical energy cost of electrical energy how to Cal the cost of electrical energy total number of units total number of units of electrical energy which we consume from where we&#39;ll get here okay into cost per unit cost per unit that&#39;s it so if you can multip mly the total number of units that is the total amount of energy energy only we are measuring terms of units that is a kilowatt hour into cost per unit if you can multiply then you will get the total cost what we have to pay clear F now we are not going to discuss in detail as the one shot video I mean already it&#39;s going to more than 1 hour okay now fine so children if you want in detail for explanation you know links will be given in the description kindly go through so each and every topic is discussed in detail okay now fine so this about the uh electrical what we can say household consumption of electrical energy so now the last one is heating effects of current heating effects of current this is a l Topic in this entire chapter I&#39;m not talking about the unit now so uh heating effects so children for suppose here is a resistor let us say Okay whose resistance are through which if I current will pass try to understand is it clear it&#39;s very very very very important so definitely some amount of heat is produced it might be electric resistor bulb fan anything some amount of you know electric energy converts into heat energy it depends on three factors the first one experimental all this proof children here so the amount of heat produced is directly proportional to the square of the current if more amount of current is passing obviously more heat is produced second one this heat produce also proportional to the resistance obviously if resistance is more then what happens more amount of electric energy converts into heat and the third one children it is also proportional to the time obviously if you are using 1 hour one electric appliance you are using 2 hour obviously what happens to the case of 2 hours only more heat is produced okay fine so this together we can write it as a h is equal to i² RT this is in terms of Jou ch children in terms of JS it also can be expressed in terms of calories or we know that one J is equal 0.24 calories so H is equal to 0.24 into i² r t calories it is in terms of calories so it is also called as J&#39;s heating law very very very very important so it is also called as J&#39;s law of heating it is also what it the J&#39;s law of heating J&#39;s law of heating is that clear children fine so this is entire chapter of current electricity again I&#39;m telling you this seems to be lengthy I think already we might have got a more than one or it might be one or 20 minutes or 30 minutes okay but children nowhere we compromised we try to cover each and every topic may not be in detail just in a shortcut we covered here the that&#39;s what I told you if you want in details of a discussion just go through the uh description there I will give you link so that you can find you know detailed explanation for each and every topic is it clear fine children so children uh again I&#39;m telling you here the ultimate source for you to have a good preparation is actually what textbook so you must read the textbook so whenever you are in the textbook just keep a notes with you so try to note down some important points so those that notes will be very helpful for your revision so after that kindly go through the ex what we can say example questions discussed already in the textbook after that you have to go through the excise question so that what will happen you will have a complete what we can say preparation about that particular chapter so that you have uh enough confidence to face the questions which are going to be given in the exam okay thank you so much all the very best

hello children in today&amp;#39;s class we are going to cover the entire chapter of current electricity so children once again let us think about this chapter so in this chapter we have three units in a unit a we will be covering about the concept of charge current potential resistance and ohms law of factors affecting the resistance finally choice of material means how we are going to choose a material for a uh different purpose okay fine whereas in a unit B we will talking about the EMF terminal voltage potential drop internal resistance and the combination of the resistors there only we will learn about the series and parall combination whereas in a unit c purely we&amp;#39;ll be discussing about electrical energy electrical power and household consumption of electricity I mean how are we going to calculate the what we can say cost of electricity so generally we will be using a uh electricity right so how are you going to to pay money for that so that will be covered in a unit c children this chapter seems to be lengthy but in fact it is a easy one to understand if you can go step by step if you can go step by step definitely what happens this chapter is going to be very very easy in the previous classes we learned already the concept of charge so let us recall once again what happens when two non-conducting bodies are rubbed each other children one body will lose some charge where another body will gain some charge let us see one example so what happens when glass rod is rubbed with a silk cloth here in this process children glass rod will lose electron means there will be transformation of charge from glass rod to Silk cloth which means what here glass rod is losing some charge whereas silk cloth is gaining some charge due to which here glass will become positive chargeable whereas silk cloth is silk cloth will become negative chargeable one children what is the unit of charge here so the SI unit of charge is Kum so when you want to measure the less amount of charts we use mum which equal 10 powerus 3 Kum micrum which equal 10 - 6 Kum nanoc which equal 10^ - 9 Kum children then how can we determine the quantity of charge or what we can gain by an object it&amp;#39;s very very important so if you want to know that first of all we should know what will be the charge of of electron so we all know very well that so the charge of electron is - 1.6 into 10 power - 19 kums so here the quantity of charge is determined by the number of electrons if more than number of electrons are there definitely charge will be more if the less if the less the number of electrons are there definitely the charge will be less on that particular body but how can we calculate the total amount of charge on the body for suppose children on one body only one electron will be there let us say for example then what will happen the charge of that body will be minus okay let us talk about the only magnitude 1.6 into 10^ - 19 kums if there are two electrons are there then two * of 1.6 into 10^ minus 19 three electrons are there three times four electrons are there four times if there are n number of electrons are there then how to calculate the total amount of charge so if there are any number of electron then the total charge Q is given by here Q is given by so plus or minus here n into e see here in some textbooks it will be given n into small q also so we can use small q or small e to represent the charge of the electron don&amp;#39;t get confused so this is how we can calculate the total amount of charge actually total amount of charge then here one important point we need to understand so since that time we talking about the Kum so Kum is a charge but the question is that how children each and every electron has some charge right but how many electrons together can constitute a charge of 1 Kum this a very very very important examination point of view let us see here means for example to have q is equal to 1um charge here how many number of electrons should be there actually so e is equal to what here let us take 1.6 into 10 power -9 kums Kum Kum gets cancel here so n is = 1 by 1.6 into 10^ -19 so this will be n is equal to 6.25 into 10 power 18 electrons children you can imagine here means these many electrons together will constitute a charge of one Co so if I say that 1 Kum charge is going like this then you should imagine that 6 25 into 10 18 electrons are going try to understand so that much what we can say you can imagine you know the quantity of a chart it&amp;#39;s very very very small and even electron is very very tiny so here 6.25 into 10^ 18 electrons will constitute a charge of 1 Kum is it clear just copy it and charge is a scalar quantity so in exam they might ask for one Mark is chart scalar Vector so obviously you can set the scalar only now children let us see a concept of current so first of all what is a current children here so current is actually general term actually what does it mean it means that something which is in flow so for example if water is in flow we can say water current actually if heat is in flow we can say it&amp;#39;s a Heat current means whatever something if it is in flow means we can call it as actual current but what is electric current children if charges are in flow then we can say that it is a electric current actually in this chapter soall current electricity we&amp;#39;ll be talking about the charges which are in completely motion only so here the current which means what you should understand whenever we say it&amp;#39;s a current so you should think it as a electric current only so electric current what does it mean children here so the charges which are in motion will constitute electric current me how much amount of charge is going in a particular time only we can say it as a electric current for suppose children here for suppose here here is a conductor through which small charge Q is going in a small interval of time then how can we write here so current is written as charge per time so children it is for a very very very small actually when you go for higher class we can write DQ by DT actually but now it is not needed actually when you learn about the differentiation then you&amp;#39;ll get that concept of what we what the importance of DQ and Delta Q all these things so now you can learn it is a IAL to Q BYT for suppose children here in this for example n number of charts are going n number of charges then what the total charge total charge will be n * of Q or you can also write n * of V nothing is wrong in it then what is the total current total current can be Q by T it is a q BYT or even you can write I is equal to n e by T so this is how we can calculate the total amount of current is it clear fine so what is the current the rate of flow of charge is called electric current children what are its SI units let us see here it&amp;#39;s SI units so here we know that I is equal Q by T Q is measured in terms of Kum T is measured in terms of time sorry T is measured in terms of second so here current is measured in terms of Kum per second this Kum per second only we can call it as a ampere this one we can call ampere the symbol is capital A a small amount of current if you want to measure then we can use here milliamp which equal to 10^ - 3 amp whereas microamp which equal to 10 power - 6 aamp and even Nano a which equal to 10 power - 9 aamp is it clear fine then how can we measure the electric current children we measure the electric current by using a device called it is a ameter and the very important thing is that ameter is always connected in series so it is always Con in the series that&amp;#39;s fine and here you make get one out so here sir what actually ampere so how can we Define ampere examination point of view this defin is very important for suppose children here is here if charge of one Kum is Flowing if charge of 1um is flowing in a 1 second time means here if one Kum charge Flows In know 1 second of time through that area of crosssection of the conductor then we can say that the current is equal to to the 1 ampere but how does the current flow is a important question children here how does a current flow so here current always flows from high potential very very very important high potential to current always flows from high potential to low potential so here we are getting a one more word called potential is it clear fine now we will see what is the potential and how can we measure the potential and and what are its units just copy this so that we move to the potential and as like a charge even electric current also scalar quantity only now we see what actually potential and what is the potential difference also for suppose let us say here is some electric field let us say here is some electric field just think here is electric field somewhere one charge is there children here so what type of charge charge it is it is children it is unit positive charge unit positive charge actually it&amp;#39;s this also we can call a test charge it is also called a test charge actually it is not available only in assumptions only it is a possible what is the test charge children the charge which is influenced by other charge but which cannot influence other charge so it is highly impossible only here is a theoretical purpose concept purpose assumption purpose only it is a possible okay for suppose children this charge is placed at a infinite distance children let us suppose here now what is our task we have to bring this unit positive charge from where from Infinity to a point in a electric field children don&amp;#39;t you think see in our in general also if you want to move anything from one point to another Point children definitely some work is done obviously yes sir yes now don&amp;#39;t you think that for this process in this process some work is done yes for what work is done is a question here to move a charge what type of charge unit POS chge from where from Infinity so children here the amount of work done the amount of work done to move this unit POS charge from Infinity to a point in electric field is called electric potential so electric potential is nothing but what children it is nothing but the work done to move unit postive charge from Infinity if W is a work done and Q is a charge then mathematically electric potential is defined as work done by charge work done by charge if you know the potential if you know the charge how can we calculate the work done obviously W is equal to V * of Q we can use is it clear fine and what s unit children yes here W is measured in a JS charge is measured in a Kum so here J per Kum it is also called as it is also called as volt V LT children we know very well that whenever we are writing a units make sure that first letter should be a small one it should be a small letter is it clear so here the s unit of electric potential is Vol but how can we measure the potential by using a device called what Vol meter by using device called Old meter that is fine then what is potential difference children children here as like a charge electric current potential also scalar quantity only okay now we see the potential difference potential difference small difference will be there between potential and potential difference for suppose here here is a point a point a and here is point B let us see that here so here we can see that now the potential difference between these two points is equalent to the work done by charge then you make get a one out so what is the difference between the different definitions of potential and potential difference very simple so to define the potential we are assuming charged infinite distance but whereas here for potential difference the distance between these two points well defined so let us recall once again what is electric potential the amount of work done to bring unit positive charge from Infinity yes or no yes now what is the potential difference the amount of work done to move a unit POS from one point to another Point within the circuit is called potential difference is that clear fine so for this also units are same that is J per Kum simply we can say the Vol is a old so when you can say that the potential difference between two points is equal to 1 volt it&amp;#39;s very simple when you can see that if one J work is done to move one Kum charge then we can say that the potential difference between these two points is equal to the 1 volt and here also we use a device so called what is that Vol meter very very very important so here volmeter is a device which is used to measure the potential difference between the two points and here voltmeter is always connected in parallel voltmeter is always connected in parallel is it clear children fine so this is a concept of potential and potential difference now we come to the concept resistance here children what is the resistance the term itself will give you a meaning resist means what stop resist means what stop means who is stopping here material who is stopped charges very simple charges in the sense electrons means whenever the electrons are moving through a conductor there will be some abstraction given to the flow of charges by the material this abstraction given only we can call it as a resistance then you may get one out so what is the reason for this abstractions that yes so if you can see the material children so in that positive Char also will be there but do you think that practically positive charges will move no they won&amp;#39;t move actually so they&amp;#39;ll be uh mean they&amp;#39;ll stick to particular places but whereas when these electrons are moving then what will happen you know they may have collisions with the charges I mean positive charges even they have collisions among themselves also is it clear fine so the very very very very important thing is that here children so what is the resistance here what is the resistance children here the abstraction given to the flow of charges by the material by the material is called resistance here okay fine so what is the s unit of resistance so resistance is measured in ohm in ohm so the symbol we can write like this here is a oh we can write but here the very important thing is that children what is the reason children so here what are the reasons for resistance why electrons are given some what we can say resistance the first thing is that here collisions so here collisions between collisions between electron and positive charge electron and positive charge and what is the second reason children it collisions among the electrons collisions among the electrons collisions among the electrons so these are the two reasons in examp they&amp;#39;ll ask you just you can write directly these two reason is it clear fine and here children the very important thing what is that here on which factors does the resistance depend examination point of view this concept is very very very very so here distance mainly depends on four factors here so the first one is it depends on nature of the material nature of the material nature of the material I mean what here different materials will offer different resistance if you can take aluminium copper children both might be a conductor but still they also offer resistance and that two they are differ because their nature is different and whereas the second one is that temperature this is very very very very important so here resistance also depends on temperature here we need to learn an important point so in the case of a conductor children in the case of a conductors here resistance is proportional to the temperature as temperature is increased definitely resistance of that conductor increases but whereas in the case of semiconductors in the case of semic conductor resistance is inversely proportional to the temperature which means what if you can increase the temperature the resistance of a semiconductors decreases clear fine and here third one is length children here so Here length of the conductor Here length of the conductor or length of the material whatever it may length of the conductor mean as length of the conductor increases practically it has been proved that even resistance also increases but what is the reason as length increases so they will undergo Collision for a long time so due to that what will happen resistance is increased so here resistance is proportional to the length so this also can be written to compare the resistance of the two materials if their lengths are given but make sure that they must be made up of with the uh same material okay fine and the fourth one is area of cross-section area of crosssection area of cross-section so experimentally it has been proved that here resistance is inversely proportional to area of cross-section so even area of cross-section for a conductor I mean you know it&amp;#39;s a thin wire so wire can be written as children here of course area of crosssection of a thin wire can be written as &amp;lt; r² so even we also can write R is inversely proportional to the r² so from this I can write here R1 by R2 is = to A2 by A1 so from this we can write it as a R1 by R2 is equal to R2 s by R1 squ you don&amp;#39;t get confused here capital r is a resistance of the material R is a radius of the wire actually is it clear fine children so these are the factors on which resistance of a material depends is it clear fine children now here only we need to learn one more thing what is that here conductance we need to learn about the conductance so what is the conductance children here so we can rep with the G in some textbooks it can be even with the c letter also it is nothing is wrong but you have to mention what is that particular symbol so what is the conductance children here the reciprocal of resistance is called conductance so here the reciprocal of resistance is called conductance and its units are its units are so reciprocal right it is a 1 by ohm or we also can addite ohm inverse or we also can addite more MH or we can write as a cmen of course now we are not using these units but this unit we are using actually of course these four are the units for conductors excuse me so these four are the units of conductance only children what is the conductance the reciprocal of resistance is called conductance so its units are semen clear fine so now children so here we have two conclusions R is proportional to L and R is inversely proportional to a so from here from these two conclusions now we are going to get a One More Concept so now we will see what is a resistivity soal specific resistance soal specific resistance so here we got R is proportional to L and R is inversely proportional to 1 by a so from this two we can write R is proportional to L by a children here here is a proportional symbol is there can we repl by a constant so we can add here R = row into L by a children this is general formula to calculate the resistance of a material if its length and area of cross-section is no know but here the point is that what is this row is called so this row only we can call it as a resistivity resistivity resistivity or specific resistance specific resistance specific resistance specific resistance and here it&amp;#39;s very very very important it depends on only two factors children it depends on only two factors what is that it depends on nature of the material it depends on nature of the material and it depends on the temperature it depends on the temperature and one more one more very important thing is that it does not depend on the what we can say length and area of cross-section which means what for example 1 M length copper wire 100 m length copper wire both specific resistance is same that is one is to one only why that&amp;#39;s what I tell you it is a what we can say characteristic properties of M characteristic property of a material so it remains same for a same material children though means though you can change its length though you can change it area of cross-section the resistivity doesn&amp;#39;t depend the resistivity depends purely on nature of the material and the temperature Clear fine and what are it units so let us see the units of resistivity units of resistivity so let us rewrite the formula for resistivity this can be written as R into a by L so your resistance units of resistance is what ohm okay area of crosssection M square and length is meter meter meter can so finally the units of resitivity are ohm met so these are the units of resistivity units of resistivity but how to define resistivity how to define resistivity so look at here if if a is = 1 M squ and L is = 1 M then mathematically row is is equal to the r only which means what here resistivity is nothing but the resistance of the material whose dimensions are unit I mean what whose area of cross-section and length are one unit is it clear so this what actually resistivity and the resistivity formula resistiv units and factors on which it depends children I I&amp;#39;m telling you on which factor does not depend also very important it it doesn&amp;#39;t depend on the length it doesn&amp;#39;t depend on the area of cross-section it only depends on nature of the material and temperature is it clear so how to define resistivity children resistivity is nothing but the resistance of the material whose area of cross-section and length are one unit clear fine now here what is conductivity what is conductivity so conductivity symbol is Sigma so what is a conductance children conductance is a reciprocal of resistance similarly similarly conductivity is a reciprocal of the resistivity conductivity is the reciprocal of the resistivity and what are it units children here it is 1 by oh met or we also can write Cen Cen meter inverse so this is a concept of resistivity and condu just copy it now we discuss about the ohms law children what is ohms law actually for what it is actually children so ohms law will give the relation between amount of current which is passing through the circuit to the potential difference across across a conductor I mean to say that here means it is stated in 1826 so examination point of view it&amp;#39;s a statement condition circuit diagram is important let us see a circuit diagram first so that you will understand very easily this is how actually the circuit diagram so here is plus minus and here is a battery this is key here is a resistor here your start so when key is on so there will be a flow of current there will be flow of current children here two points see examination point of view sometime they might give this circuit diagram they ask you to find the what we can say errors in that circuit diagram so mostly you know where there will be a question you know in the place of voltmeter they might give ammeter in the place of ammeter they might give voltmeter children always remember that old meter must be connected parallel ameter must be connected in a series so examination point of this circuit diagram is very important okay fine so what does OHS SL State children so OHS SL state that the amount of current which is flowing through the conductor or a resistor is directly proportional to the potential difference across it ends across dense is it clear fine so this can be written as here so here V by I is equal to constant experimentally it has been proved again I&amp;#39;m telling you experimentally it has been proved this constant only we can call it as a r that is a resistance again I&amp;#39;m telling you for a what we can say at a given temperature we are talking for a given material for a given length for a given area of crosssection the ratio of V by I remains constant so this can be written as V isal to I this is a mathematical form of ohms law V is equal I is a mathematical form of ohms law so what does it State children so OHS states that the amount of current which is flowing through the conductor is directly proportional to the potential difference what we appli across it ends but what are the conditions here so physical condition should remain same I mean what temperature pressure must be same then only what happens this ohms law is valid so in examination point of view even they may ask you about the condition also when this HS law is valid so you have to write that yes when temperature and pressure that the physical and physical conditions remain same then only it is applicable fine okay so based on oh children here so resistor soal conductors you see don&amp;#39;t get confused you may get one sir resistor is different conductor is different why are you using children each each and every conductor offers some resistance don&amp;#39;t again I&amp;#39;m telling you so you we do not have a conductors with a zero resistance any conductor offers even at least some resistance is it clear so if I use conductor resistor don&amp;#39;t get confused okay fine so based on the H SL children here we have two types of resistors one is omic resistors another one is non ohic resistors so first we will see omic resistors or we can call omic conductors also nothing is wrong omic conductors so what are omic conductors children so the resistors are the conductors which obey which obey ohms law which obey Oh&amp;#39;s law are called omic resistors or omic conductors and children so in this case children for the very very important that in the case of omic resat the relation between potential difference and current is a linear that&amp;#39;s what these resistors are also called as linear resistors linear resistors linear resistors then how the VA graph and IV graph will be there for omic resistors we&amp;#39;ll see so this examination point of very very important so it is a I here is V children so we get a straight line which is passing through the origin so what is the slope of V gra will give you so here slope of V graph that is what y components by X components that is V by I is nothing but what children resistance children examination point of VI it&amp;#39;s a very very important but here only there will be a confusion let me tell you so this is about the VA graph but if you can make a IV graph if you can make a IV graph so this is VA graph now let us make it the IV graph i v graph so here for same values this will be V here is I so still you get a straight line passing through the origin so for this slope slope of IV graph slope of IV graph will be y components that is I by V children V by I is equal R but I by V is equal 1 by R 1 by R is nothing but what conductance conductance so here don&amp;#39;t get confused here so in exam they ask a question what is the slope of va graph VA graph will slope of V gra will give you resistance but whereas the slope of IV graph will give you conductance so this is what actually the clarity we should have okay fine so what are the examples for om almost all All Metals All Metals comes under omic resistance is it fine okay now we see hope it is Cy children take this fine now nonic resistors children let us see nonic resistors non omic resistors so you can guess which do not obey which do not obey ohms law which do not obey ohms law and children here in the case of nonic conductors as they are not obeying the ohms law so the relation between the potential difference current won&amp;#39;t be linear it is nonlinear that&amp;#39;s what the resistors also called as nonlinear nonlinear resistors nonlinear resistors so examples for this lead and filament of bulb filament of bulb even diodes even transistors all semiconducting materials will come under this nonic resistors now how the vi graph will be there for this VI graph children very very important so it is like this nonlinear and one more thing is that it is not compuls that this graph should start from the origin it may or may not it is so what is the slope Children Here slope of VI graph of the nonlinear Condor so as a nonlinear direct you cannot take a v value and I value we can take only change in what we can say potential by changing current that is here Delta V by Delta I so Delta V by Delta I will be Delta R it is nothing what dynamic resistance Dynamic resistance Dynamic resistance means what it will vary children dynamic means what it&amp;#39;s not a constant so it will be changing is it clear fine so this is about ohms law and omic resistors and even nonic resistors just you can copy now we see the choice of material yes children now we&amp;#39;ll see the choice of material children depends on the purpose we are going to pick up so depends on the purpose so we need to pick up the material with the different properties actually so here first for suppose children if you are using for a correcting purpose for suppose here uh for suppose here electrical connections electrical connection so usually we can prefer either copper or aluminium but what should be the properties of this electrical connection children so here these wires whatever we are going to pick up the material I me to say that so they should have low resistance and high melting point they should not melt easily is it clear fine and here the second one is standard standard resistors which we&amp;#39;ll be using in a laboratory purpose actually so here the very important they should have high resistance High Resistance and they should not depend on they should not depend on temperature I mean the resistance should not vary with the temperature and here the examples are very important examination point of view it is mangine it is mangine even constant constant t or the examples for standard resistors and here third one is fuse one wire children fuse fuse wire about this so we&amp;#39;ll be discussed in household circuits in detail actually so fuse wire the very important thing is that here fuse wire should have high resistance High Resistance but low melting point and your fuse is made up of with a lead and Tin lead and clear fine and the next one is so it&amp;#39;s a fuse wire and let a filament wire children it is filament so for a filament purpose generally we use tungsten right we use tone so what should be the property children it should have high resistance and high melting point both should be high only both should be high only now heating element children heating element I mean generally we&amp;#39;ll be using for a water heaters right example I&amp;#39;m telling you so made up of with a nicrome made up of with the nicrome and what&amp;#39;s the properties here so eating hel that particular material should have high resistance High Resistance and high melting point high melting point is it clear so these are the first we should know the properties of that particular material based on that only we can pick up we can pick up for what we are going to use Clear fine last point in this unit I can say so as we discussing actually you know one sh video I cannot say last topic and all this but as I said that so unit wise you can go preparation so after unit wise preparation you can go for a one short revisions all the things okay okay so in this I&amp;#39;m talking about the super conductor and super conductivity children this are very very very very important super super conductor super conductor children in the case of conductors we know that here resistance is proportional to the temperature I mean what if you can increase the temperature resistance also increases okay that is fun but what happens when we decrease the temperature children yes so when we decrease the temperature children obviously resistance must be decreased so if you go on De the temperature to very very very low and the resistance goes on decreasing decreasing decreasing and at a very very very particular low temperature it has to be zero is it clear means at very very low temperature very very very low temperature what happen the resistance of the conductor is zero where the conductivity will become Infinity the conductivity will become Infinity is it clear that conductor in that position we can say super conductor means the conductor with zero resistance at a very very very low temperature is called super conductor this phenomena is called super conductivity example Mercury so Mercury can behave like a super conductor below 4.2 Kelvin So Below 4.2 Kelvin here super what Mercury behaves like a super conductor children super conductor means what here The Temper very low temperature resistance will be zero resistance will be zero means what conduct ity must be a Infinity okay just copy this fine so children now we discuss what is the electromotive force what is a terminal voltage what is the potential drop what is the resistance and how they are related children examination point of view this is very important even we can expect the numericals based on this also okay now fine so now let us see children so first if you want to know that first we should know what actually electric cell is so let us make electric cell first and here is negative terminal children we know very well that actually so here what we can say electric cell which maintains the constant potential difference between two conductors by a chemical reaction to obtain a constant flow of current and what kind of energy mean there will be a you know what we can say transformation of energy right so here electric cell which converts the chemical energy into electric energy the symbol is what children so the symbol of cell will be like this minus and a plus is it clear fine now let us see children do you think is a closed circuit or open circuit obviously a closed so it&amp;#39;s a open circuit it&amp;#39;s not a closed circuit because here no resor is connected right it is purely purely open circuit means whenever we bring a new electric cell yes this is its position so electric if you can see electric cell CH on that something is written in terms of volt that is nothing but actually what we can say it&amp;#39;s a EMF electromotive force electromotive force can means we have two types of definition it can be defined in terms of work done also so how can we Define a work done so before that children first we&amp;#39;ll discuss in terms of potential difference children here is a open circuit right here so here the potential difference across the open circuit only we can call the EMF so simply what is EMF Children Here EMF is nothing but the potential difference between the terminals of a cell in a open case means in open case in open circuit in the case of open circuit the potential difference between these two terminals is nothing but the EMF but it also can be what we can say different in terms of work done for suppose one charge is there here so to move this charge in entire circuit entire circuit children so work must be done that is what socaled total work done so the total work done to move a charge in entire circuit is called as electromotive force or electromotive force is nothing but the potential difference across the open circuit that&amp;#39;s it across the terminals of the cell in an open circuit in an open circuit so here EMF simply I can write here electr motive force can be written as total work done by charge total work done by charge so it is also so what we can say J perum so it also can be measured volt only okay and which factors this EMF depends children so here EMF depends on mainly two factors EMF depends on two factors one is nature of the electrolyte nature of the electrodes let us say first nature of the electrodes what type of electrodes are we using their nature and the second one it also depends on the nature of the electrolyte nature of the electrolyte and children it does not depend on few Factor it does not it does not depend on the following factors on which factors for suppose it doesn&amp;#39;t depend on the size of the electrod children size of the electrodes it does not depends on the size of the electrodes and also depends on the distance between the electrodes distance between the electrodes and also it also what does it depend on the amount of an electrolyte amount amount of an electrolyte Electro light is it clear so this is about actually electromotive Force I&amp;#39;m telling you what is Electro motive Force here what is electromotive force the total work done to move a unit posi charge in entire circuit I mean inside and outside inside and outside I&amp;#39;m telling you is called electromotive force or electromotive Force simply we can Define as a potential difference between the terminals of a cell in a open circuit is called electromotive Force so it depends on nature of the electrodes and nature of the elect it does not depend on the size of the electrodes distance between the electrodes and the amount of an electrolyte clear fine now we see what is a terminal voltage what is terminal voltage now children here so now so far it is in open circuit let us connect children here now okay now we are going to connect to a one resistor let us say it is current to the resistor okay then what happen happens current starts flowing current start flowing now don&amp;#39;t you think that it is in a closed circuit yes so here terminal voltage terminal voltage so usually children terminal voltage we represent with a V so what is the terminal voltage terminal voltage also can be can have two definitions children here so what is the first simple definition terminal voltage is defined as a potential difference between the terminals of the cell in a closed circuit whereas EMF is in open circuit whereas the terminal voltage let us recall once again what the terminal voltage it is the potential difference between the terminals of the cell in a closed circuit is called terminal voltage another way also we can Define children this is completely outside of the cell we can say external this is internal so from let us say Point uh let us say Point C Point D so here to here to move move a charge some work must be done yes or no so the amount of work done to move a charge in an external circuit or outside of the cell is called terminal voltage so this I can Define as a small W by Q so for this also units are Vol only for this also Vol only clear fine now we discuss about the potential drop potential potential drop Will rep the small V what the potential drop okay so terminal voltage nothing but what work done in in what we can out what in exal circuit out the cell but don&amp;#39;t you think that inside also charge has to be moved yes for that also for that some work must be done that work done only we can call as a potential drop I mean what here potential drop is a work done to move the charge within the cell children within the cell so we can the w- by Q for this also un needs volt only children now if you can see here if you can see here electromotive Force terminal voltage potential D these three are work done only three what makes the difference here so here children w- by Q is a work done to move charge within the cell whereas W small W by Q is a work done what we can say to move the charge exteral circuit if you can add these two what you&amp;#39;ll get here total work done to move the charge total work done to move the charge entire circuit this outside of the circuit is the inside of the circuit this is what total circuit this is so this is nothing but what actually EMF so it is EMF is equal to this what potential what we the terminal voltage plus this is what potential drop children this is a very very very very very important def important relation it is okay fine children now again I&amp;#39;m telling you whenever you want to calculate whenever you want to calculate what get the terminal voltage you only consider external resistance so how to calculate this terminal voltage terminal voltage is equal to Total current in the circuit into external resistance only external resistance only but to calculate the potential drop you need to multiply total current into internal resistance we&amp;#39;ll discuss internal resistance don&amp;#39;t worry about it okay now try to understand so if you want to calculate about the if you want to calculate the terminal voltage total current into external resistance if you want to calc the potential drop total current into internal resistance now you substitute here you&amp;#39;ll get here i r + i r here you can take I into r + r is equal to EMF so this is EMF is equal to if you want to Cal the current it is is EMF by total resistance that is internal resistance and external resistance so this is how we can calculate the total current in the circuit if if resistance and EMF is known is it clear just copy it now we discuss about the internal resistance we discuss about the internal resistance fine can this yes CH what is the internal resistance children inside of the cell what will be there electrolyte will be there it might be the conducting material but as I told you earlier even copper and aluminum might best best conductors still they offer some resistance similarly here this electrolyte also offers some resistance so the resistance offered by an electrolyte within the cell is called internal resistance is called internal resistance so examination point of view also this a very very very important internal resistance children purely it is offered by electrolyte only electrolyte so the resistance given by an electrolyte within the cell is called internal resistance will repes with a small letter children this internal resistance depends on intern resistance depends on first one surface area surface area of electrodes children so here inter resistance is inversely proportional to the surface area of the electrode and the second one is distance between distance between the two electrodes children distance between the two electrodes so here in resistance is proportional to the distance between the two electrodes whereas the third one is temperature so experimentally it has been proved that here inter resistance is inversely proportional to the temperature so fourth one is concentration of an electrolyte concentration children higher the concentration of electroly higher is a internal resistance is it clear so there are the four factors surface area of the electrodes distance between the electrodes and temperature of an electrolyte temperature of what electrolyte and the concentration of okay so concentration of an electrolyte so there are the four factors on which internal resistance depends fine children here then how EMF uh internal resistance external res terminal voltage or related is very important based on this we have numericals ch here so interal resistance is equal to we can write as a ex resistance into EMF by terminal voltage minus one children based on this we have a numerical children it is most most most most wanted for examination point of view usually we are getting a numericals even in Bard also so here small R is equal to see children what is the capital r external resistance small R is what here internal resistance it is a EMF and terminal voltage children once again let us recall what is the difference between EMF and terminal voltage what is EMF children here the potential what we can say difference between the terminals of the cell in an open circuit what is the terminal voltage here the potential difference between the terminals of the cell in a closed circuit is called terminal voltage is it clear fine now children here we have combination of resistors so here under this combination of resistor children we have two types of combinations first one is series combination second one is parall combination first let us see series combination series combination here so see children here first when we can say that resistors are con Series so to make the situation simple just will consider only two resistors so let us see two resistors its resistance is R1 and its resistance is R2 So This Is How They are connected in the circuit plus minus the potential uh difference between the cell is let it offers V let us say that here so now when you can say that two resistors are in series when you can switch on this so the current should pass like this same current I same current I so two resistors are set to be in series if same amount of current can pass through that resistors it might be two or 100 res if same amount of current is pass through 100 resistors then you can say those 100 resistors are in parallel okay so the first condition is what here current must be same current must be same through all resistors whereas here potential difference is divided very very very potential difference is divide among the resistors for example V is the total potential difference let us see that across this it is V1 across this it is a V2 which means what here in a series connection current is a constant but potential difference is divided among the resistors connected and the total potential difference can be written as in this case V1 + V2 if more number of resistors are connected V1 plus V2 plus V3 plus blah blah blah like that it can be okay now is it clear fine then how to calculate the total resistance if two resistance are connected children the effective resistance in a series connection is equal to the sum of the resistance of the individual resistors individual if more number of resistors connected so what we have to write we have to write as a R1 + R2 + r 3+ so on plus rn rn for suppose children all these resistance all these resistors have equal resistance then r s is equal to n * of R this is how we can calculate the total resistance that is fine but here examination point of view if two resistors are connected like this they might ask calculate the potential difference across R1 across R2 so across R1 we can write like this V1 is equal to very important I into R1 by R1 + R2 whereas to calculate vs2 V2 is equal I into R2 by it is R1 + R2 so these two formulas are very important to calculate the potential difference across the individual resistors across the individual res so children here so what I this is a conclusion actually so the the total resistance is always greater than that of the resistor with the maximum value in that combination so how to calculate here just you can add resistance of all resistors then you&amp;#39;ll get the resultant resistance clear fine now we discuss the parallel comination we discuss the par children in a series combination two points are very important what is that current must be same through all resistors whereas potential is divided now the second combination is parallel so second combination is parallel so how the connection will be again I&amp;#39;m telling children so we are considering only two res if you want you can take more than two also no one will question you okay so it is R1 and here is R2 so common points okay here is B sorry key key and cell getting battery nothing is wrong plus minus now if you can switch on this what happens current start flowing but here there are two paths are there so definitely what will happen current will get divided among the resistor but how if more resistance is there less current will pass less resistance is there more current will pass in that manner the current will get divided okay so the first important point of this is that here the potential difference is constant across all resistance con to parallel whatever the potential difference will be there same will be there here same will be there here but what makes the difference here current is divided here current is divided among the resistors current is divided among the resistors such way that the total current is equal to the currents which are passing through the individual resistors the current which is passing through the if you can add all those current then you&amp;#39;ll get the total current clear fine and how to calculate the effective resistance if two resistors are ConEd parallel children here the the reciprocal of resultant resistance is equal to the sum of the reciprocals of the individual resistances children very very very 1 by RP is equal to 1 by R1 + 1 by R2 if more number of res are connected plus + 1 by rn rn if all resistors have equal resistances equal resistance are then how do calculate the resultant resistance resultant resistance RP is equal to R by n RP is equal to R by n is it clear fine uh here examination point of children here here I told you that here current will get divided but how to calculate the current which is passing through the resor one and resor 2 very important so it is i1 is equal to so total potential is a constant anyhow that we know very well that is here is R2 by here R1 + R2 R1 + R2 whereas for I2 which is equal to V into it is uh not sorry it is total current I should be there right okay I by R1 + R2 so this is how we can calculate the total amount of current I mean the currents which are passing through the individual resistors examination point of view numericals can be as based on this okay just copy it okay now we discuss the electrical energy children let us recall once again law of conservation of energy so what does law of conservation of energy St children so according to law of conservation some energy energy neither be created nor be destroyed but it can be transferred from one form to another form children electrical energy is the most desired form of energy for suppose you can take electrical bulb what will happen electrical energy is converted into light energy some part even heat energy also if you can take a fan electrical energy to mechanical energy if you can take electrical heater electrical energy to what heat energy in fact children we cannot imagine modern world without electricon energy is it clear so is that means electric energ is that much important so it&amp;#39;s very it&amp;#39;s a responsibility to know what act electric energy and how it can be calculated I mean right fine so let us take a simple circuit to understand this let us say here is resistor with a resistance R and Pro with the cell which offers potential difference of v and let say key okay so when key is on what happens so current starts flowing so children already we discussed about the potential what is the potential if current is passing means what charge is moving as charge is moving means what here some amount of work is done so that amount of work done only we can call it as a potential difference how it can be defined children so your potential difference is defined as work done by charge from here only we can call it as W is equal to VQ don&amp;#39;t get confuse here the work done is equal to the electrical energy so now on words we are going to use electrical energy I mean symbol as a w only don&amp;#39;t get confused so here is a electrical energy so this is the first Formula to calculate electric energy if you know the potential difference and if you know the charge and children we know that here okay let us see second one second form of electric energy we know that V is equal to or okay we know that here I is equal to Q BYT from this children Q is equal we can it now here you can substitute here so then you get W is equal to v i or v i t sorry V it t so this a first Formula and is a second formula okay fine and children from the OHS law we know that V is equal I right V is equal I now you substitute V is equal R in this place so then what you&amp;#39;ll get W is equal here it is I S RT i s RT is a one more formula you calculate the electrical energy now children so from this ohms law only V is equal I that is fine only but from this can we write I is equal VR yes we can write this you can substitute in this place you get W is equal that is v² by r² into R into T r² cancel so here is w Is = v² by R into T children these all are the formulas to calculate the electrical energy you make it one doubt actually so which formula I should remember or I should use is not like that we should remember and we should use so we have to use a formula to carry electrical energy based on the data given in the numerical is it clear fine and what are the units of electrical children yes obviously the S units are Js only obviously JS only is itally fine so before going to discuss about the commercial units of electrical energy we need to learn about the electrical power is it clear fine Children See don&amp;#39;t get a power confusion with power children why means in the 10th class especially we have power in mechanics you know work power energy there we discuss about power whereas even we discussed in a lenses power of a lens different okay and here is electrical power don&amp;#39;t get confused don&amp;#39;t get confused still generally what is the power in terms of mechanics also the rate of doing work the rate of doing work is called power but here how to define at what rate electric energy supplied by The Source or at what rate electric electric energy is consumed by the resistor is called actually power so simply we can see that here power is equal to Children power is equal to electrical energy electrical energy by time electrical energy by time so in the simple terms power is equal to we can write it as a W by T okay this is a direct formula you can use okay so don&amp;#39;t get confused here we have a few you know Expressions to car electric energy so let us recall once again W is equal to v i t w is = i² RT uh W is equal to what we got here v² by R into t means in each case if if it is div with the time time time time if divide with the time divide with the time divide with the time what you&amp;#39;ll get electrical power the simple Lo logic logically think if you can remove time term then you&amp;#39;ll get the electrical power simple so here second expression because it is by time right div with the time what you&amp;#39;ll get here power is equal to VI I third one so here Al if you can divide with the time what you get power is equal to i s r fourth one if you divide with the time what you get here power is equal to v² by R so these are the Expressions to calculate the power so what are the units of power children yes uh it is measured in a watt so if huge power if you want to measure you can use here kilowatt or megawatt or it&amp;#39;s a gig kilowatt is very very important here please remember this kilowatt fine okay now we see the commercial units of electrical energy commercial units of electrical energy commercial very important examination point of view commercial units of commercial units of electrical energy children we know that actually power is equal to work by time right okay sorry it&amp;#39;s not work by time electrical energy by time so then electrical energy can we write as a power into time yes now power is measured in a what time is measured in a second so what into second can be a unit of electrical energy but the thing is that here so measuring what electrical energy in 1 second time it will be very less for example what is energy consumed with the refrigerant in 1 second can you pay electric bill for that 1 second no it is not at least for one month means what at least we need to measure time in terms of hours at least you should measure 1 Hour 2 Hour 3 hour that&amp;#39;s what you know so time in the place of second we can take as a hour is that clear so here wat hour I telling you if power is measured in wat then wat hour is a commercial of electric energy if power is measured in terms of kilowatt then kilowatt hour exactly fine then wat hour is equal see in examination point of view how wat hour and kilowatt are related to the Jou they will ask you children 1 wat hour is equal to 3,600 JS whereas 1 kilowatt hour is equal to 1 Kow 3.6 into 10^ 6 J children this is actually commercial unit of electric energy this only we can call the unit so whenever we are talking about the electricity build children we will talk right how many units have we what we consumed 50 units 100 units so so one unit means what here 1 kilowatt hour if we have consumed 10 units 10 times of this much 100 units 100 times of This Much okay now so here kilowatt hour is a commercial unit of electrical energy is it clear fine and now we will uh talk about the power rating children so what is the importance of power rating if you know the power rating what benefits are we going to get what information are we going to have children whenever you can see whenever you want to purchase actually electric appliances we must see the power ratings actually so something is written for suppose example it will be written like this 100 W example I&amp;#39;m telling you 100 wat and 220 volt so like this it is written so this actually power rating by knowing the power rating what information do we get so children first of all we will come to know about the resistance of that particular uh what electric appliance when it is in use how let us see here so from this power is given here 100 wat okay and the potential difference is 220 volt 220 volt so we know that actual power is equal to v² by R so from this here R is equal v² by P so R is = 220 into into 220 by it is 100 so R is equal to 484 ohm so this much amount of resistance that particular Appliance will offer if its power rating is this much Clear fine and what is the second benefit we are going to get so we will come to know about the safe limit of current Ching what is that safe limit of current means what maximum current can pass through through that particular Electric Appliance if if current will exceeds what will happen that particular Appliance will get fused okay fine so we know that P is equal V into I so I is equal it is a p by V so here you can substitute the values so this will be p is equal to how much 100 by 220 if you can substitute 0.454 approximately 0.5 aamp which means What that particular Appliance with this much power rating uh can bear only up to this much this a limit of the current what happens if current exceeds this as I told that it will get fused so this what actually information we have by what we can if you know the power rating of an electric appliance okay just copy it now we see how to calculate the cost of electrical energy consumed children here as we as we discuss discussed earlier what actually commercial units of electrical energy means whatever the electrical energy which we are using children that can be measured in terms of kilowatt hour soall unit is it clear so one unit means what 1 kilowatt hour 2 units means what 2 kilowatt hour so how to calculate the first of all electrical energy children here so electrical energy electrical energy so as I told you that it must be measured in terms of kilow hour only kilowatt hour only so for this you should know the power of electric appliance power must be kilowatt only and how many hours we are using that electrical appearance so if you know the power and if you know how much time it is used then you multiply you&amp;#39;ll get the electrical energy simple it is but sometimes power may not be even given kilowatt then what we have to do here so here for suppose here power is given only in terms of what but here time is given in terms of hour okay then you must divide with th000 then you get it sometimes power might not be knowing you might be knowing about the potential difference in current still we will we will why we know p is equal VI I so then so either formula you can use to calculate electrical energy okay once electrical energy is done then what we have to do yes cost of electrical energy cost of electrical energy how to Cal the cost of electrical energy total number of units total number of units of electrical energy which we consume from where we&amp;#39;ll get here okay into cost per unit cost per unit that&amp;#39;s it so if you can multip mly the total number of units that is the total amount of energy energy only we are measuring terms of units that is a kilowatt hour into cost per unit if you can multiply then you will get the total cost what we have to pay clear F now we are not going to discuss in detail as the one shot video I mean already it&amp;#39;s going to more than 1 hour okay now fine so children if you want in detail for explanation you know links will be given in the description kindly go through so each and every topic is discussed in detail okay now fine so this about the uh electrical what we can say household consumption of electrical energy so now the last one is heating effects of current heating effects of current this is a l Topic in this entire chapter I&amp;#39;m not talking about the unit now so uh heating effects so children for suppose here is a resistor let us say Okay whose resistance are through which if I current will pass try to understand is it clear it&amp;#39;s very very very very important so definitely some amount of heat is produced it might be electric resistor bulb fan anything some amount of you know electric energy converts into heat energy it depends on three factors the first one experimental all this proof children here so the amount of heat produced is directly proportional to the square of the current if more amount of current is passing obviously more heat is produced second one this heat produce also proportional to the resistance obviously if resistance is more then what happens more amount of electric energy converts into heat and the third one children it is also proportional to the time obviously if you are using 1 hour one electric appliance you are using 2 hour obviously what happens to the case of 2 hours only more heat is produced okay fine so this together we can write it as a h is equal to i² RT this is in terms of Jou ch children in terms of JS it also can be expressed in terms of calories or we know that one J is equal 0.24 calories so H is equal to 0.24 into i² r t calories it is in terms of calories so it is also called as J&amp;#39;s heating law very very very very important so it is also called as J&amp;#39;s law of heating it is also what it the J&amp;#39;s law of heating J&amp;#39;s law of heating is that clear children fine so this is entire chapter of current electricity again I&amp;#39;m telling you this seems to be lengthy I think already we might have got a more than one or it might be one or 20 minutes or 30 minutes okay but children nowhere we compromised we try to cover each and every topic may not be in detail just in a shortcut we covered here the that&amp;#39;s what I told you if you want in details of a discussion just go through the uh description there I will give you link so that you can find you know detailed explanation for each and every topic is it clear fine children so children uh again I&amp;#39;m telling you here the ultimate source for you to have a good preparation is actually what textbook so you must read the textbook so whenever you are in the textbook just keep a notes with you so try to note down some important points so those that notes will be very helpful for your revision so after that kindly go through the ex what we can say example questions discussed already in the textbook after that you have to go through the excise question so that what will happen you will have a complete what we can say preparation about that particular chapter so that you have uh enough confidence to face the questions which are going to be given in the exam okay thank you so much all the very best

Transcript for:Current Electricity Lecture Notes

Transcript for:
Current Electricity Lecture Notes