 Okay. Hello guys. Good evening. So, as we are over a result agnostic approach of achieving great grades in 10th standard exams approaching soon. Okay. So, today is the first revision class of physics. As the screen and the title indicate, we will be going through, we will be going through the chapter electricity. Clear. Sure. Easy. Very good. Okay. So, I am just verifying whether the broadcasting has started or not. Clear. Sure. So, all of you who are there can see me. Easy. Sure. Please, let's start the lecture. So, we will be going on through certain topics. Okay. Sure. Clear. There will be theory discussed. There are some numerical aspects of the chapter. So, when we talk in whole about electricity which was there or which is actually there in your 10th standard. Okay. Science. Clear. Sure. We primarily discussed about we have done right. So, we will be revising about we have primarily discussed in the class about how conduction happens. Clear. Then the Ohm's law. Clear. Analyzing the figurative or schematic representation of a circuit also known as circuit diagram. Okay. Understanding different parameters and devices of attached in a general circuit. Clear. And parallely solving numericals based on them. Clear. Easy. Sure. I am re-verifying whether you guys can see the screen or not. Cool. This is it. Sure. So, when we talk about the electricity it's all around you. We are communicating or I am sharing my thoughts to you with the help of the word electricity. Though electronics is also involved into it. That's a different division. Okay. That's a totally different vertical. We will not be discussing about that at least in 10th standard. Clear. Now, from this chapter when we talk about 10th board exams when we talk about 10th board exams from this chapter. Okay. Dominantly, three to four questions are possible. Okay. Sure. There is a good possibility that a big question that is of five marks which is also included in your pattern will come. Though your five markers are also kind of an integration of some small, small questions. Clear. When we talk about the conceptual part of questions asked, yes, there are certain laws and definition like Ohm's law. Okay. Sure. From which the question may come. Clear or not. Sure. When we talk about the numerical aspect surely the same Ohm's law solving a circuit equivalent resistance. Okay. We will also come. Sure. In general, people also discuss about the domestic electric circuit in this chapter. Okay. But we will be dominantly talking about that post finishing the chapter magnetic effects of electric current. Clear. So, for today's lecture which will continue for the next tentative two hours. Okay. We will be discussing about the basic revision electricity. Sure. Clear. Sure. Electric current and circuit. Actually, the story starts with charge. Yes or no. Charge symbolically represented by a small Q or capital Q has got its SI unit as capital C Coulombs based on dedicated to the scientist who discovered it. Yeah. Just a second. I think few students have a problem with logging in and witnessing this lecture. So, let's continue. So, talking about the charge. Right. So, charge symbolic representation small Q or capital Q. The SI unit is cool based on or dedicated to the scientist who discovered of primarily defined. Clear. Sure. Pause that. Pause that. The current comes. Okay. So, by definition if I will ask anyone of you. Okay. Or you might be thinking as soon as we talk about current you say the word or the line the rate of flow of charge is called current. Right. This whole chapter is primarily introduced to you to cater the knowledge that why the charge move. Right. So, when you were in ninth standard you had this discussion, right or not that Newton's first law state that until and unless a force will be applied on any particle having some mass the particle won't change its state of motion, right or not. So, if charge is shifting from one place to another not only a single charge a good amount of charges, right or not. Sure. So, when charges are shifting from one position to another then there must be some reason behind that, right or not and that reason is the second point that is electric potential. Clear. The potential is the reason why charge move. Clear. Sure. And the potential difference causes the flow. Sure. Potential difference is denoted by capital V. We call it volts. Volts. Easy. Easy. Someone has switched on. Hello. Check one. Check one. Check one. Check one. Hello. Check one. Check one. Hello. Check one. Check one. Hello. Check one. Check one. Hello. I think if you can mute your mic that will really help us because I am getting an eco back. Now it's really good. Thank you. Thank you very much dear. So, continue. So, when I generally take this case I consider or I just try to explain you with a very practical example. As of now all of you guys are very comfortable at your respective locations. At your home, right or not. You are receiving it at a very stable point. You guys are stable. Okay. Sure. For example, if I bring you all in this dark room. Okay. Sure. And put you here. Sure. So, for a while as I have brought you, you may be in a stable position but after some time you will not be right or not. You will feel restless and you will tend to move. Clear. It's something very same as work done. When charges are at their respective location, we make them move. In general what we do is we make electrons move. Okay. We do this excitation either by chemical processes or by mechanical processes in generator and magnetic effects and all that is different vertical. But yeah. When we talk about a cell, a very small source of potential. Okay. So, it is nothing but by chemical processes. Right or not. Sure. When we have done some work on this charge, this charge has got some energy and now this energy is making it restless to move. It's simple. So, as soon as they will get a conducting path, as soon as they will get a conducting path, they will start moving. Simple. Sure. Sure. So, all these collection of charge at the point is known as the potential. Sure. Then as here it's a higher potential and outside through the conductor there is a lower potential. So, charges will tend to move from higher potential to lower potential through a conducting path. And as it is a rule of life that no path comes smooth. There surely be disturbances. Okay. In any path. These disturbances on electrical grounds are known as the distance. Easy. Sure. So, we create a potential difference because of which current will come. Sure or not. Clear. And within this journey, this energy will not be just utilized to run, but will also be utilized to fight the obstruction in the path. V is equals to IA, the Ohm's law. Easy. Sure. Clear. Okay. So, sorted with it that what is an electric circuit? It's a schematic arrangement of charges on which work is done by some process. Now, these charges have some energy. As soon as they will get a conducting path, they will move. Moving charges will introduce current and that current will flow through conductors. While movement, these charges will experience some resistance from the conducting path. Okay. Sure. And hence, a part of their energy will be utilized over there. We will call this energy utilized over a resistance or fighting over a resistance as potential drop further in the chapter. So, easy with the introduction part of the chapter. Clear. Not talking about the further. Card 2. What is charge? Have I introduced you very well with this? Sure. Easy. Very good. Sure. So, what is charge? Here. When we talk about the types of charges, then it is very simple. Positive and negative. But when someone talk to you or ask you about movable charge, then the answer is just electron that is the negative charge. Remember here that protons being inside the nucleus never get shared. Okay. When a material and element loses electron, it become positive. When something receives electron, it becomes negative. As simple as that. Clear. The SI unit is coulombs. Clear. Sure. Now, when we talk about property of charge, then the charge by nature is quantized. Clear. Sure. This is not frequently asked in CPSC, but okay. Just for the introduction part, I will just take it. See here. If you know the Dalton's atomic theory, he proposed that an atom is the smallest block or particle which cannot be further divided and then came the modern atomic theory which stated that no atom can be subdivided into electron, proton and neutron. Sure. So, now these three particles are not or cannot be subdivided. That means when we talk about electron, it has got the fundamental charge of 1.6 into 10 to the power minus 19 coulomb. And as this electron cannot be broken, this implies that the smallest possible charge is this. That means wherever the charge will exist, it will exist as an integral multiple of the fundamental charge. Okay. N belongs to integers. Right or not? If N is positive, that is charge transferred is positive. What does it mean that the electrons are taken out from the body? So, what body has is a positive charge. Where electrons are given to a body, what is the negative charge? Simple. Fundamental charge is 1.6 into 10 to the power minus 19 coulomb as it is a charge of electron, by default it is negative. Sure. Here charge will, flows with respect to time will make current, the general line. You can also write it as that current is rate of flow of charge. Sure. No doubt. The unit of current when we talk about is ampere, not ampere, no, ampere. Okay. The unit of current is ampere. In general, in CVSC board exam, it's one of the routine questions for almost all the derived units. Okay. Not the fundamental units. Almost all the derived unit, they ask define. Okay. Like define ampere. Okay. So, it is very clearly stated here. Define ampere. One ampere. Okay. Sure. Is defined as the current when one coulomb of charge flows in one second of time. By mistake, bache, this second has to be small. Okay. Small s. Clear? Sure. Sorry for the printing mistake but c has to be capital and even ampere has to be capital. So, easy. Clear? Very good. Now, the measuring instruments. Okay. I'll talk about them a bit later. Not as, not really now. I'll surely come back. Okay. I'll talk about them later. But as we have discussed about the schematic representation of a circuit, a circuit will have a voltage source. Clear? A conductor which will be having current and surely there is a resistance. Now, this line doesn't mean that over here only like breakers on the road that over here only there is resistance. No. This is just kind of a schematic representation. The resistance is throughout the wire. We don't have any really existing thing which is a superconductor. Okay. So that which will have zero resistance. No, this is not possible. Clear? Any material, the best conductor which is silver, noted down, the best conducting material is silver. Okay. Even that will have very minor resistivity. Clear? What is resistivity? We'll define it if you know, smile and revise. Clear? Now, this symbol which I have made actually won't signify the voltage source, but just to tell you. Okay. Not talking about primary symbols used in a circuit like you can see here. Okay. Sure. This is for cell. Multiple cells will make a battery. The longer one is the positive terminal, the shorter one is the negative terminal. As I have already represented here, this zigzag is a resistance. Okay. This is bulb or any load actually. Sure. Any kind of load as of now when you are in tin standard will be denoted by this symbol. It can be a fan but as it is a load, as it is a power consuming device within the circuit. Clear? Sure. So, this will be signified by this symbol. Okay. Then there are some minor things like there exists a key. Some places it will be drawn like this. This means that the circuit is working. If it is just like that, the circuit is not working. What does that mean? The switch is on, the switch is off. Clear? For that, we have measuring instruments integrated with the circuit. Ammeter and voltmeter. Meter as the name indicates is the device used to measure current. Voltmeter in the device used to measure voltage drop or voltage. Note down one part that ammeter will always be connected in C. The voltmeter will always be connected in F. Okay. Sure. Why? So, here when the question is right, all you need while revising the question, chapter 2. Okay. Switched on the mic of the system. Please ask. If not, please mute the mic. These are the symbols which we have talked about. Sure. There are multiple more. I will just discuss about this reosted which is really important because there will be a question in your exam. Write the circuit arrangement for verification of Ohm's law. Only there you will use this. Okay. Reosted. Reosted also known as variable resistance. Okay. Is an arrangement of wire wound over a cylinder or any hole. Okay. The resistance of a wire has got its relation with the length. We use that principle in order to vary the resistance for a reosted. Clear? Not only this, even this symbol as they have drawn here indicates the reosted. Also known as in common words the variable resistance. Sure. Clear? Here they have indicated positive and negative terminals for voltmeter and ammeter. Sure. Clear? Note them because when you will see the device, yes they will be indicated as positive and negative. Sure. No doubt. Clear? So, now we are moving ahead. Ohm's law, the very fundamental and very important law. Something which is primary to be asked from this chapter. The Ohm's law and the graphical representation of voltage and current for a good conductor. Clear? Sure. So, the complete name of Uncle Ohm is this which is stated there. Clear? George Simon Ohm. Sure. As I explained you that the circuit is working on the energy given and this energy given not only gives rise to the speed that is the rate of flow of charge but also fights with the obstruction in the path. Right? So, the energy given is utilized into two verticals V is equals to I. Uncle Ohm. I have just simplified the understanding of it. Uncle Ohm stated something. Okay. Which give, which has provided this clear idea. Sure. That across a conductor, this is a conductor. Okay. As I said, there is no conductor in this world which will have zero resistance. Resistance will be there. Clear? So, across any conductor, the current drawn is a directly proportional to the voltage applied. In order to remove this proportionality and bring equality, a constant was required. Post experiments, this came as the resistance. Clear? Sure. Now, this was also experienced as this is a linear relationship. So, if you plot voltage versus current graph, it will be a straight line. Clear? So, there comes a question. What are ohmic and non-ohmic conductors? Okay. So, see, simple answer is ohmic conductors are those which follow Ohm's law. Non-ohmic conductors are those which may conduct, which do conduct but not give a straight line. Let us do, do not follow the Ohm's law. Now, what kind of conductor are they? Clear? So, broadly speaking, there will be a different vertical when you go into electronics, the semiconductors. Semiconductors don't provide adjust for the sake of knowledge. I am giving you this idea. Semiconductors don't follow Ohm's law. They are non-ohmic but conductors. Why? Second, even when we go deeper into the electricity and understanding, okay? Sure. Clear? Inductors, capacitors, there will be some conductors behaving or conducting electricity but their behavior will not be just resistive. They will have inductive and capacitive effects also. In those cases also, sometimes ohmic nature is not observed. Sure. Easy. Just for the knowledge part of you, as of now, for 10 standard inductive effects, capacitive effect will never come into picture. As I am repeating again and again, we as a team will have to be very clear about that this whole thing is very much concentrated over scores and scores will need a systematic approach. Clear? Sure. Easy. So, we will divide it into two verticals. Yes or no? Once the theory is being discussed, as of now, we are revising the chapter. We are revising the concept behind the chapter. Parallel, there are problem-solving videos of previous year questions which are asked from this, okay? Mostly the questions will fall into numerical aspects. Whenever we feel that there is a need to explain a theory-based question, like defined Ohm's law and all those kind. So, whenever we feel that, we will also upload those kind of questions very soon. Clear? Sure. So, Ohm's law stated something. The mathematical expression of Ohm's law is on your screen. Clear or not? Easy. Sure. Very good. Now, talking the next age data. Understanding the Ohm's law gives a clear understanding how the circuit problems will come. Yes or no? Sure or not? V is equals to IR. Now, we will explore what this R is. As I said the word resistance. Right or not? Sure. Resistance. What is resistance? Just by definition, mere definition states that the obstruction in the flow of charge is called resistance. Clear? Just like the word meaning. Sure. The SI unit of resistance is Ohm's as stated here. Sure. The symbolic representation looks like this. Omega types. Clear or not? Now, this resistance of a material is due to a property resistivity. So, recently I was solving one of the previous year papers and it is very clear we asked, defined resistivity. And the answer to it is resistivity is that property. As I said, as life has got a property that no journey in this life is obstruction free. Similarly, there is a property. Okay. The property by virtue of which any material shows resistance is resistivity. Clear? Easy. Sure. It is denoted by the letter Ohm. Also, it has got a derived SI system. By definition, resistance of a material is R is equals to rho L by A. Sure. So, where L is the length of the wire and A is the cross-sectional area. Length of the wire, meter. Cross-sectional area of the wire, meter square. So, the unit of resistivity is Ohm. Meter and meter got cancelled, one meter. Clear or not? Ohm meter. Sure. Now, how the resistance is rho L by kind of by experiments, but we can conceptually develop the intuition of that. See, if you have to do a journey, like if you ask your father that Papa, I want to go for a ride, then he'll ask. Okay. Sure. To a distance. If distance is very high, there is a very long, not high. Okay. There's a higher probability of you meeting an accident. I don't know. There is a higher probability of having an obstruction. So, resistance is directly proportional to length. But if the same rod is very wide, six-lane, four-lane system, then there is a lesser probability of meeting the accident, unless and unless you are drastically right or not. Sure. So, resistance is inversely proportional to the cross-sectional area. I don't know. Sure. So, by intuition, resistance is equals to rho L by A, where rho is the core property of the material. Rho, that is the resistivity is the core property of the material. The resistivity of a material will not change. The resistivity of a material will not change until and unless the physical properties associated with the material are changed. That is, if you will increase the temperature, yes, you will observe a change in resistivity. Sure. By just changing shape and size of the material, change in resistivity will not be observed. Okay. Sure. Easy. Clear. So, now factors on which the resistance depends. Clear. The length, the cross-sectional area and the resistivity. Easy. Sure. Now, from here, surely a question comes. Okay. What I'll just state an example. Very straight. There are two types of questions which arise here. Cutting a wire and compressing or stretching a wire. Compressing or stretching a wire. Okay. What is the difference to see? If I say that the resistance of a wire R1 is 2 ohm. Clear. What does it mean? Rho L by A. If this wire is cut into two parts, what is R2? That is the resistance of any one part. You will say, okay, R2 will be, resistivity will remain same as just cutting is done, just by cutting or compressing that is just by bringing change in shape and size, we cannot bring change into resistivity. So, resistivity will remain the same. As you have cut it, like this is the wire, this has been cut. The cross-sectional area will not change. So, A will remain same. But as you have cut, the remaining, what you are calculating is having the length half. So, it is having L by 2. Right or not? L by 2. Now, you know very well that the value of this box is 2 ohm. This 2 is here, 2 into got cancelled. So, 1 ohm. Yes or no? Sure. Easy. Clear. Whereas, if I have done the same thing by compressing that mean initially resistance was 2 ohm. The wire which was initially of length L and cross-sectional area A is compressed to another length which is L by 2. Clear? What will be new resistance? So, now answer very simple straight. See, as you have been through a chapter known as surface area and volume in your ninth standard, you know that while I am doing this that is compressing the wire, the volume will remain same and you will write a line over here. What? That volume is equal to length into cross-sectional area. Yes or no? Right? So, as volume is same then volume initial is equals to volume final. Right or not? Volume initial is equals to volume final. That means L1 A1 is equals to L2 A2. We are very much aware that L2 is half of L1. So, L1 A1 is equals to L1 by 2 A2. L1 and L1 got cancelled. 2 goes there. So, you know that A2 is 2 times A1. So, R2 is equals to rho instead of L2 L1 by 2 instead of A2 2 A1. So, here the resistance finally was half of resistance initial whereas here the resistance final is 1 by 4 times. 1 by 4 times the resistance initial. Got this? Sure? Clear? So, you can kind of see I do not want you to memorize many things but yes just in order to save time if you can generate this idea and keep it saved in your mind then for example a wire by cutting. Yes or no? Note one. Cut. Clear? If L final is equals to L initial by N then R final is equal to R initial by the seamen whereas for compressing okay if L final is equals to L initial by N then R final is equals to R initial by N square. Say for example, see cutting you can not do that anything but yeah suppose by stretching if you have converted the length to 2N then what will you write that? See L final is equals to 2 into L initial. Can that be written as L final upon 1 upon 2? Must just make it here and enjoy. Easy? Sure? Clear? Very good? 4 times. Yes or no? Simple? Sure? Excellent. So, this is the primary way of asking the question based on the formula R is equals to L by A okay. Also just to trick you sometimes they give you all these changes and then ask you what is the ratio of final to initial resistivity not resistance. Resistivity. So, if that is the case then your answer will be one this one sir because till the time the temperature is changed the resistivity will not change just by changing the shape and size we cannot bring change into this term resistivity right or not? Sure? Easy? Very good. Clear? So, clear with the intuition of resistivity? Easy? Now talking about the resistance of combination clear? So, when we talk about the physics part tilt and standard at least two wires can be corrected in two ways either in series or in clear? This is known as series arrangement this is known as clear? Now the combination measures a resistance and that resistance which can be also stated as net resistance is technically stated as R equivalent. What is equivalent resistance? The total resistance offered by a combination of resistors is known as the equivalent resistance simple. So, our motive as of now while revising this topic is to revise that what will be the and how will be the equivalent resistance of a series combination and a parallel combination. Clear? Sure? Can we? So, before going into that I hope you remember the intuition that that when we connect two wires in circuit in series then the current remain same whereas when we connect two wires in a circuit in parallel then the voltage across them remains the same. So, first case taking the case of series combination I will take it with two resistances R1 and R2. This is the applied voltage V. So, now you know that as they are in series the current will remain the same. So, the voltage at V1 plus the voltage at V2 is equal to the total voltage that is the total voltage is equal to V1 I R1 V2 I R2. The total voltage is nothing but I into total resistance which is our equivalent I R1 plus I R2. I take in common and cancel. So, you get this line that for this combination R equivalent is equal to R1 plus R2. So, if there are n such resistances, resistors R equivalent will be equal to R1 to sum Rn. Clear? This is the concept of series. Clear? Now, when we talk about the parallel but before going into it there will be individual voltage drops on these. These are V1 and V2. Clear? V1 can be calculated by I into R1 and V2 can be calculated as I into R2. Now, talking about the parallel arrangement. Yes or no? As we had the current same in series arrangement, so do the voltage will remain same in parallel arrangement. Clear or not? You can see the schematic representation. They are done by 3. I am doing it by 2. Suppose voltage is supplied to a combination of two resistors connected in. Sure? This is R1 and this is R2. Clear? The voltage applied is V. So, now what you are very much aware about is the voltage drop at both of them will be equal and that will be equal to V itself. Right or not? Easy? So, now see. If I know that there is a current going inside whose value is I then there is a current I1 here and there is a current I2 here and the I1 and I2 will come out. So, I can write a very simple line that the total current supplied is getting divided as I1 and I2. By the Ohm's law that is V is equals to IR I can write I is equals to V by R. So, total current supplied is the total voltage supplied upon the total resistance we call it equivalent resistance. I1 is equals to V1 which is V itself upon R1 and I2 is equals to V2 which is V itself upon R2. Taking V common and cancelling you get the equation that 1 upon R equivalent is 1 upon R1 plus 1 upon R2. If there are n such then 1 by Rn. Serial just for the star part of it just to simplify your efforts if there are two then directly by taking LCM you can say R equivalent is equals to R1 R2 upon R1 plus R2. So, the unit will remain same as home until unless they themselves are stated as mili ohm, micro ohm and all that. Clear or not? Easy? So, so this was the discussion regarding combination of registers. Clear? And deriving and deriving how the equivalent resistance in series is R1 plus R2 and how the equivalent resistance in parallel is 1 upon R1 plus 1 upon R2 and so on. Now, this is very important part the disadvantages and advantages of series and parallel over each other. Clear? So, we will discuss it in domestic circuits where you will understand it better. As of now I am kind of just leaving it. Clear? Easy? Very good. Now, before going into the heating effect of current we will understand the power in an electric circuit. Clear? Sure? And then we will also discuss about the power consumed in an electric circuit. Clear or not? Sure? So, coming back to this the power. Okay? After that we will just discuss 1 or 2 circuits. Okay? To solve them and simplify them. When we were in class I remember we have also discussed about wheat, stone, bridge and all. Dear, I have solved multiple papers around 11 papers I have seen and in no paper there was any single discussion of wheat, stone, bridge and all. Okay? You guys remember it from the exam view. Okay? Sure or not? Clear? So, don't be worried about it. The numerical aspects which we have discussed in our classes is way higher than what will be ours in the exam. I am very confident about it and pretty hopeful also that you will crack those numericals very well. Anyway, you will surely get a good link and good connection, collection of numerical approaches ready for the exam. Sure? Now talking about the power. I don't know. So, as you know that here there is some work done to move that electron from some position to bring it into battery and it is moving. So, there is surely some transaction of energy happening. Some work is happening and work done per unit time is also known as power from your 9 standard definition. Right? Okay? Very good. So, in an electric circuit, the power is stated. Okay? The power is stated as voltage multiplied by current. Electric power is stated as voltage multiplied by current. At least when we are talking about DC, when we will talk about AC alternating in nature and all, we will have another formula stating Vi cos theta and all that. Okay? So, as of now, we will keep ourselves binded to V into I. Now, how this heat and all, try to not to see. Very simple arrangement and clear? You will understand it well. By Ohm's law, if I write V into I then V is equal to I R. I can write this as V into I one type or I square R another type or V square by R another type. All these three terms. Clear? From these, actually this one is generally heat loss. Okay? So, whenever someone asks you about what is the heat, it is an energy. This is power. So, energy is equals to power into time. So, heat is equals to I square R into T. Simple? Sure? Clear? So, when you actually supply V into I, this is the work done, the actual effective and utility work done and this amount of heat is lost as heat. This amount of energy, sorry, is lost as heat. Clear or not? So, when we talk about the efficiency of a system or of a device, we just calculate it by V square by R and Vi, not in DC because in DC, you will see that there is rarely any loss, right or not? Clear? So, all these three are the power formula. Here in 10th standard, I will suggest where the circuit is in series, use this formula for power. When the circuit is in power, we use this formula for power. When you directly know the rated things, you can calculate by this. Clear or not? Sure? We will do it in while doing the problem solving, problems, okay? Related with this chapter, electricity. Understood? Clear with the intuition of power and heat energy and all? Clear? Sure? Very good. Now, what are the applications of heating effect of electric current? Right? So, see, we use electricity for different appliances. We do have an AC at home or we see an AC at home, an AC at home. We also see a room heater, sorry. So, not only for cooling the room, we also use electricity to heat the room. So, based on our requirement, we apply the electricity, right or not? See, when we talk about that the heat is I square R, clear or not? Okay? When I need to generate more heat, then I will take a material which is better, okay? Sure? Heat. So, which will have a higher resistance, right or not? It will generate more heat, like heater. But when I have to not use this as a heater, but to glow my room, like bulb, I will use a material which will have a very low resistance. Yes or no? So, I square R will not cause much heat, but the more amount of electricity will be utilized to generate light. Simple, sharp, clear, no doubt, okay? Like it's very clearly stated here. I just read it that filament of a bulb is made of strong metal with high melting point such as tungsten, okay? Why? Because when you give it, okay? Sure? The heat, it should not melt. Clear or not? This filament can retain as much of the heat generated as possible. It will retain the heat, it will not transmit the heat. Clear? Sure? Instead of transmitting the heat, what it will transmit, it will emit light. Simple, sharp, understood? Very good. Now, commercial scale of these energy, commercial measurements related to energy. I'll write it transactions, which one? Commercial. So, see, everyone of us get a bill at home. Is there anyone who is watching this and not getting an electricity bill? Please tell me what is the method, okay? Sure? So, jokes apart, when we consume electricity, we got a pay. Whatever energy we consume, we do some transaction, some exchange right now, maybe money or maybe some other efforts and all that. So, here when we take electricity from the electricity board, we got to pay them and they charges on the amount of energy, right or not? Consume. Now, when we talk about energy consumed, energy is being, is what we are being charged on. We see on the bulbs and all the devices, watts, wattage is the power unit. So, in order to move from power to energy, we got to multiply a time. So, the unit of electrical energy is what should be actually into watt seconds, but serial. This is the SI unit. But when we talk about the commercial scale, we use too many watts and for long duration. We don't get a minute-to-minute bill, right or not? We get a bill for month and when we use the second and just watt for month duration, the number stated will be very low. So, what we have done is we have constructed a commercial unit of electricity. What is it? It's kilowatts consumed in R, kilowatt R. What? Sure. Clear? We are charged based on how many kilowatts R we have consumed. Like for example, I have a bulb, right? Only one bulb at home, okay? Sure. So, I have a bulb at home. We'll just say for example of 100 watt. Now, this bulb glows for 4 hours every day, consider it a month of 30 days. If the price, they will just say the price, the rate of electricity in the city is 5 rupees per unit, 5 rupees per unit. Charges rate is 5 rupees per unit. Then what will be my monthly electricity bill? Considering I have only one appliance. So, you'll say, okay, the utility what Sir is saying is 4 hours every day multiplied by 100 watt for 30 days. So, see this is my watt R, right or not? 1000 that is 3000 into 4, 12000 watt R, right or not? Now, the unit is not watt R, it is kilowatt R. So, divided by kilo. So, I have unit used 12 units. For one unit, I have to pay 5 rupees. So, for 12 units, I'll have to pay 60 rupees. So, lucky I'll have only 60 rupees as my electricity bill. Simple, show, cool, very good. So, this is the intuition of power and electrical energy and the charge, okay. So, you got to pay for consuming electricity. Clear, show. So, a quick revision of the chapter is done. Now, I'll talk about two or three appliances which we discussed about. When we talk about a circuit, okay, a circuit have different elements, okay. We call them as active elements and passive elements. We call them as active elements and passive elements. Clear, this is what I am telling, whatever now I am telling is not extra but kind of important, show. So, I will just, okay, some things we will talk about, some important types of question and then, okay. Primarily, in your class, you will be talking about voltage, current, resistance. Yes, for resistance, you will have resistivity also. Then, when you move to power, you have power and energy, okay, show. The SI unit of energy is watt second, okay. But commercial unit of electrical energy is kilo watt R. Power is in three formats, V into I or I square by R, the heat one apart or V square by R, the actual work done. Clear or not? A circuit, okay, will have active devices and passive devices. Active devices are those which act as source of energy, right or not? Like voltage sources, batteries, cells and all. Passive elements are those which consume electricity. Arrestance itself is a consumer. Bulb is a consumer. Even a meter and voltmeter are consumer to some extent. But we actually call them or bring them into measuring and detecting devices. Measuring and detecting devices. When we talk about measuring devices here, we have voltmeter and ammeter. By the name, this will measure voltage, will always be connected in parallel. This will measure current, will always be connected in series. The reason is the resistance of this is very low. The resistance of this is very, very high. Never connect an ammeter in series, in parallel, why? Because by that you will make the circuit short. So what is the meaning of short circuit? What is the meaning of short circuit? When two conductors directly come in touch with each other, the resistance tends to zero. As V is equals to I R, so the current flowing becomes V by R. As R tends to zero, so the current tends to infinity and I square R tends to a very high value. That causes high heat, sparks and further fire. Easy, short. Now in order to save our home from electrical damages and even to save the appliances, we use some safety devices. Okay, what are they? Like fuse, like fuse. We will discuss about questions soon. That's why I have kept a question and solution template here. Okay, we will discuss about questions soon. Okay, very soon. Don't be worried about it. Clear? So safety devices like fuse. Even while designing our plugs, we keep in mind that there has to be an earth terminal. Okay, fuse is a safety device which is made of a wire which is having a good conductivity but a low melting point unlike the bulb. For a bulb, we use a wire which is having good conductivity but a very high melting point so that it won't get fused. Whereas we want this fuse to get fused. That's why we use a wire which is having low melting point. Clear? Sure. Now what do we mean by saying low melting point? Low, low, low melting point. Okay. When I2R will happen and if extra current beyond the set limit goes, this wire will melt and the circuit will break. As the circuit will break, the other appliances which are connected within the same circuit will not get influenced. Easy? Sure. Now what is the motive of using the earth terminal? Okay. So when we use a three pin, this one is the earth terminal. This pin is thick plus long. The reason behind being thick is for the same material, if you will have big A compared to other two terminals, the earth terminal has got a higher or more cross sectional area. So with more area, resistance will reduce. That means as the current has a tendency to flow through, the path of least resistance, it will flow through the path of least resistance only. Right or not? Sure. So whenever the plug is inserted, if there is any excess current already existing within the socket, this excess current, this excess current will take the way of earth and will get earthed and hence the appliance will be saved. Clear? This is the same reason why we have it a bit longer than the other two terminals. Reason being this earth terminal will have to at least go inside first. Right or not? If there is some extra current already within the socket and the phase and the neutral terminals are going first, then these two will receive the current and which will lead to the appliance and the appliance may get damaged. That's why we also make it a bit longer so that that goes into the socket first. Easy? Sure? Clear? So now let's discuss some numericals and other types of questions which can be asked from this chapter, electricity. Clear? I hope I have made it quite clear to you through the revision. One by one, I'll be writing the question. See a very good bouquet of questions is already in the process to be made available to you as soon as possible which is a collection of previous ear salt questions for many maths that you have already seen might have already written as that mathematics they are doing in routine. Even physics I have done, at least for electricity it is over. Okay? That will be made available to you very soon. Sure? Just take some questions and understand it. Very first question, very easy. Okay? Clear? No doubt. If a wire of resistance 10 ohm, if a wire of resistance 10 ohm is compressed its length and then two equal parts, what will be the resistance one such part? Simple? So, step one of the question, there is a resistance R which is equal to 10 ohm. Now, as you have compressed it, which cycle compressed? It to L by 2 half. Okay? Clear? So, you know that the R new R dash I'll write will be equal to R initial by 4. You know it. So, 10 by. Now, this R dash is for the cut. 2 L by 2. So, R double dash will be equal to half of that. So, that will be 10 by 8. Clear or not? Easy? Sure. They may also ask what is the ratio of final to initial resistance? Your answer will be 1 is to 8. Simple? Clear? Very good. Next question please. Sorry for the wrong flow. There is some problem here. Sorry, sorry, really sorry. This is a battery. Okay? This is 5. This is 4 and 4. Clear? Sure. This is 3, 6. Clear? Sure. If there is a 40 volt battery connected, there are some questions. Okay? Question number one. What is the current drawn from the battery? Question number two. What is the current in two ohm resistor? Question number three. What is the voltage drop? Okay? What is the voltage drop at any of the four ohm? Clear? What is the ratio of power in two ohm to that of four ohm? Simple? Sure. Let's do that one by one. In any such cases, I have taken a bit bigger case. Okay? You won't get there is least possibility that you will get this kind of big case only. But sure. The first thing you are going to do is calculate R equivalent. Clear? Now, R equivalent in the circuit can easily be calculated by these three are in parallel, this one and these two. Right or not? As four and four are in parallel, the answer will be two ohm. If three, two and six are in parallel, sure? Clear? Then three and six will make a parallel combination whose answer is two ohm. Right or not? How come? R1 into R2 upon R1 plus R. Right or not? 18 by 9 is two. Clear? Now, this two is in parallel with the other two. The answer will be one ohm. Already, the five one is single. So, equivalent resistance is eight ohm. Easy. Net, which is going to be the answer of your part one is equal to V net by R equivalent. V net is 40. R equivalent is eight. So, I is five ampere. Clear or not? Simple? Okay. The third part. Now, as you know the current, you have to know the current in two ohm, which is this one. So, now you have to consider the flow. The same current of five ampere will pass through it. At this junction, the current will get divided to three verticals. One, two and three. Yes or no? Again, from here, it will be back as five and now we'll get divided into two verticals. Now, it's quite easy here. Why? Because, because, because, because these two are equal. So, 2.5 and 2.5. Yes or no? Not talking about the current in these three. For sure. Again, as three and six are making it like two and two. So, from here, the current passing is nothing but 2.5. Got it? Why? Because these two will create a two ohm resistance and now the current in that part of two ohm and this ohm has to be equal. So, 2.5 ampere is the current flowing through this one. Easy. So, the current through this is 2.5 ampere. This part is also done. The fourth one. Ratio of power. So, power can be calculated as i square r. Clear? So, ratio of power. Power in two ohm resistor is i square r that is 2.5 square into r. The ratio of these two. So, the power in four ohm resistance is 2.5 square into four. Easy question. Straight answer one is two. Why? Because these two parts will directly get cancelled. i square r and i square r. Was that fun doing this? Easy approach. Good to understand. Very good. So, this is another type of question here. So, next question. From terminal one of wire to terminal two. From terminal one to terminal two. Clear? 5000 electron passed in two seconds. What is the current? Simple. As you know that current is q by t. Instead of q what you will write is n e by t. Now n is 5000. Charge in an electron is 1.6 into 10 to the power minus 19 coulomb. By given time is 2. Quite an easy stuff. These three will make this as minus 16. This is nothing but 0.8 5s are 40. So, 4 into 10 to the power minus 16 ampere. Clear? Easy. This is the way questions are passed. One or two markers. Clear? Cool? Next question. Simple question. Next question. Two bulbs. One of 60 watt. Another of 100 watt. Rated to 220 volt each are connected across a voltage supply of 220 volt. Simple? Sure. Which one will glow brighter? Which one will glow brighter? So, simple. P1 equal to 60 watt. So, R1 will be equal to V square by P that is 220 square by, as they are rated to 220 by 60. Similarly, P2 is given as 100 watt. So, R2 will be equal to V square by P that is 220 square by 100. Just analyzing we know that R1 is greater than R. Now, power as I said when you are talking about a series arrangement just consider the power by I square R. So, power 1 is equal to I square R1 and power 2 is equals to I square R2. As they are in series I and I are equal. So, P1 and P2 will be compared on the grounds of R1 and R2. As P1 is P2 R2 to be converted and we know R1 is greater than R2 so do P1 will be greater than P2. That means the 60 watt will glow more easily. So, this is one of the disadvantages of connecting appliances in series. Simple? Now, consider the reverse case and do the same thing. Very good. See 220 is quite an obvious thing now. This is 60 and this is 100. Both are on 220 volt. Both are of 220 volt. Both are receiving the same. So, 60 watt will glow lesser and 100 watt will glow higher comparatively because both of them are actually glowing to their best efficiency. 60 and 100. But by comparison itself 100 is brighter than 60. So, simple. Power is very simple case. Now, talking about the last vertical from where the question may arise is there the consumption. So, suppose in my home their age now I will get a bit richer. There is one bulb, one fan. Now, if I have a stated fan I won't use AC. Okay, sure. So, one bulb, one fan, one refrigerator and one washing machine. Clear? The bulb is of 60 watt. The fridge is of 140 watt. The fan is of 140 volt. The refrigerator is of 20 watt. And the washing machine is of, now, boom. Okay, let's make it 180 for easier valuation but let it be. Now, this one is used per day usage, I am per day usage. Bulb for 4 hours. Fridge for 24 hours. This is fan confusing. For fan it is 8 hours. For refrigerator let it be 24 hours. And for the washing machine let it be half hour per day at an average. So, daily though we don't use washing machine. So, the question is if the rate of power is 8 rupees per unit what will be the monthly bill of a month of 30 days? Simple. In one day what amount of power the bulb is using? 240. Here, watt hours. Cool, you are going good. Right or not? 140 into 8 watt hours. 480 by the refrigerator, watt hours and 100 watt hours by the washing machine. These are the watt hours per day in a day. So, in 30 days the watt hours will be just add them all. Okay. So, this is 100, 240 is 340. Right or not? Just rough work I am doing here. Okay. 820. 820 plus 1120 is 19040 watt hours in one day multiplied by 30 such days. So, double zero I am keeping here. 340 are 24. Am I correct? No, 340 are 12. 390 are 27 and 28. 3 into 5. These are watt hours. What is the unit kilo watt hours? So, divided by kilo so it is really 58.2 kilo watt hours. Multiplied by 8 will be the answer. Easy in rupees. Oh, shit. Clear? Easy, sure. Very good. Okay. One or two questions just for the advantage of understanding the topic. Simple question, answer this. Two copper wires. Two copper look like this. Length L, length L, area A, area 4. What is the ratio of resistivity 1 to resistivity 2? Yes, anyone? Shout aloud. Hmm. Don't answer me. Don't answer me anything. Exactly. Right? I told you now by all the twists what they'll do is they'll ask the resistivity. All the twists are there. It's a one marker. One is to one because just by changing the shape and size. Okay. Just by changing the shape and size, we cannot change the resistivity. For changing the resistivity, temperature, etc., has to be changed. Clear or not? Sure. Very good. Easy. Sure. If they would have asked for R1, H2, R2 then, then it's easy. Right? Rho and L are same by A1. Okay? By Rho and L by same by A2. So the answer will be A2 by A1. That is 4 is to 1. Simple. Sure. Clear? No doubt. Very good. Sure. Simple question. Just answer. Okay. This is 1. This is 2. And this is 3o. Clear? Okay. Sure. Should be V supplied. This is V. Okay. Sure. What should be V supplied? Such that the V at 2 will be greater than V at 1. The potential drop at 2 will be greater than potential drop at 1. I have kind of damaged it. So let's make it like 4. Let's try. I'm just kind of experimenting and meeting up a question. So let's check in this case, what is the potential drop at 2 and at 1. Clear? See. The total, the total resistance R equivalent is 1 is to 8 by 6 plus 3. I don't know. 1 R1 R2 upon R1 plus R2 plus 3. I don't know. Clear? 4. 24 or 8, 32 by 6. So the current being drawn from the battery will be V by R. This is 6 not 2. So 6 V by 32. Clear or not? Simple. Now. So the voltage drop at 1 ohm resistance is 6 V by 32. Equation number 1. Now we have to know the voltage drop at 2 ohm resistance. Clear? Sure. Okay. Now you know that the voltage drop at 2 ohm will be equal to the voltage drop at 4 ohm resistance. Why? Because they are parallel. Now voltage drop at 2 ohm resistance will be equal to I into R. Now what is this I? Okay. Clear? So one part of the 6 V by 32 will go to V4 and one part will come to 2. If we have said that the part coming to 2 is I then the part going to 4 is say for example this is I net is equals to I net minus I. Okay. But instead of doing this you can directly apply current division rule which I have explained you in class. Current division rule says that the current in 1 is equal to resistance 2. Current in 2 is equals to voltage upon R equivalent into resistance 1. Simple. Clear? So similar way the current in 2 ohm is equal to the total voltage. Sure. Upon R equivalent R1 plus R2. Not R equivalent. Sorry. R1 plus R2. Okay. That is 6. Into R2. What is R2 for I1 which is this R2 will be 4. Simple. Sure. Clear? So now for all values this will be greater than this. Easy. So it was a made up question you can ignore it. I have kind of messed it up. Okay. Sure. In order to construct a new concept and all that it was very simple when I created in series for any value of voltage supplied as the current is same. Okay. Ignore this part what I was trying to state is for any value of voltage supplied if 3 resistances are connected in series. Okay. Voltage of R big will always be greater than voltage of R small. Clear? So this was what I was going to state. I kind of messed it up all over here. Okay. Clear? Sure. Fine. Next question which is going to be the last one also. This is 1. This is 3 and this is 6. Okay. Sure. A 6 volt battery is applied. Sure. The question is P1 ratio P3 ratio P6. You have to calculate this. The ratio of the powers in 1 ohm, 3 ohm and 6 ohm resistances. So simple again the ratios will be based on the current and voltage is whatever you want to take. Clear? So what I will do is simple. First R equivalent. R equivalent is 1 plus R1 R2 upon R1 plus R2 that is 3 ohm. Why? Because this is 2. Clear? The current being drawn from the battery will be 6 by 3 that is 2 ampere. Simple? Sure. So the power in 1 ohm will be equal to I square R that is 4 volt. Now for power in 3 ohm you got to know the current in 3 ohm. Right or not? So what will I do is as the power consumed by 1 is known. Now what I will do is the star line here V consumed by 3 and 6 is equal to V supplied minus V consumed by 1. Now V is equals to I into R. So V consumed by 1 is 2. V supplied is 6. So total voltage is 4 here. Right or not? Clear? So on that ground as these two are parallel I can write their power as P3 equal to V square by R and P6 equal to V square by R. Yes or no? Sure. So now when finally we have to calculate the ratio. So we have P1 ratio P3 16 by 3 ratio P6 16 by 6 whole got multiplied by by by 6. We get 24 raise to 32 raise to right or not? Clear? 16. Now if you want you can take 4 common so you will have 6, 8, 4. Further you can have 2 more common so you will have 3 ratio 4 ratio 2. Yes or no? This was a good one from me. Sorry I messed it up but yeah this was a good one. A good question. I hope the explanation is also correct. Sir can you repeat the part of power of 3? Okay much. See power can be calculated by V into I, V square by R or I square into R. Right or not? As I had to compare the two powers there were two ways. If required I would have calculated the individual currents in this and would have multiplied the I square and R. Right or not? Instead I used V square by R and for calculating the voltage drop at this box what have I used for calculating the voltage drop at this box? What have I used is the voltage drop at this box will be equal to a supply voltage minus voltage utilized by 1 ohm. Right? So the voltage utilized by 1 ohm is I into R 2 into 1 so 2 volt. Right or not? Clear? Supplied voltage is C 6 minus 2 so total voltage falling at this box is 4. Clear? As these two are in parallel so their individual voltages will remain equal. Power at the 3 ohm is V square by R. V is 4 so 4 square by R that is 3. Similarly power at 6 ohm will be equal to V square by R. V is 4 so 4 square by 6. Easy much? Thank you sir. Okay. So further is mathematical simplification taking 4 common and all that. Okay? Sure. Best of luck. So signing off sorry for messing up with one or two numericals I think one at least the last or second last one I have messed it up. Hope the chapter is thorough with you. Clear? We will shortly attach a list of previously asked questions and numericals along with the chapters they are ready and will be available very soon. Clear? So if any question it's not open house you can throw it up now. Clear? Okay. Thank you guys. See you in the next lecture. Thank you sir. Thank you sir. Okay dear.