hello and um welcome to this video in this uh video we'll be talking about um two subjects that is the voltage sources and the current solar sources and we will see how we draw their symbol so the objectives here is the uh walter sources of course with their symbols and current sources and their symbols and then we will do examples so on this one here we will looking at the voltage and current sources we have two types of sources one of them is the most familiar to you you've seen it most likely and that is the independent sources independent sources um we um we drew we have two uh sources and that is the voltage sources and current sources the way we draw the current source by convention and as a standard is we will have a circle and there's two terminals of course for the voltage source the positive terminal and negative terminal so it's just like a circle and then we will for the positive terminal with a plus inside of the circle and negative terminal we will put a negative inside of this circle and of course then we will put next to it the uh that's whatever that voltage source we've just put v to say this is a voltage source and of course if we know the value we would put like 10 volts 5 volts 2 volts whatever that 40 whatever that value so that is the voltage source as you can see two terminals do it with positive and negative and the circle that is a symbol to represent it and then we will have the current source and the same way we will have it as also a circle and we have the two terminal going in and coming out and with instead of putting a terminal uh like a positive and negative here we will just put an arrow to represent that there this is a current source and so there's just like the current is going through and this is the direction the error points the direction of the current so it's it's going in from the negative terminal and going going out of the positive terminal and so we'll just put that the value that is i to say this is a current source and the current could be one amp one milliamp um whatever that value is and so a voltage source this is so this is the common way we we have it another common way we might have this is to um draw it like we draw it for uh battery so it depends on the um the company that is using this dropping the circuit we could draw it as in this uh symbol with this symbol or we can draw it as just like a battery we will draw for a battery and that is uh in this fashion so this is the symbol for a battery and of course we will designate the positive terminal and this is usually the negative terminal and the same thing we will say this is the volt so this is just another common symbol for voltage so that either one some some companies they will just choose in circus they will use this to represent just batteries usually and but it can be this one can be used for like a bench dc supply or um or just another um battery or like an outlet so it depends how we want to draw it so we can draw it in this fashion if we want to designate it as just a battery we'll just draw draw it like this so you will see the two uh conventions here um being done like that so this is the the symbols for the voltage source and the symbol for the current source let's let's do an example on this um here we have given this circuit below we have the circuit in which we have again this is the power supply positive negative and its value is 3 volts and so we will designate this is the positive this is the negative we don't have to do that but just for the beginning that's um that's good to start there uh just putting where the positive and negative so you can make it easier for you to understand and then we are connecting it to some load and we designate that load since it is unknown load we usually designate it as a box empty box you could say this is the load writing l as node and then this is connected to the battery or whatever that power supply that we have and and then we can designate this is the positive and this is the negative of this terminal and let's say this is v1 so now in this fashion we want to find so this is the load this load can be anything can be the outlet it can be the appliance like refrigerator whatever that uh load or another circuit that we might have or is just another element like a resistor or capacitor or inductor or another circuit so that that's the so here in this case we want to find question we want to find v1 so you will see that now looking at this setup how that this is um this is parallel uh setup in which we will see that the positive terminal is connected to the positive terminal so um so you can see here the positive with the positive and then the negative with the negative so this is a parallel uh setup and said so that is the case if we put a probe then from the battery across this load um i mean if we want to prove it and we want to measure what's what's in here we will measure what's the voltage across the um across this voltage supply or power supply so in this case we will see that that v1 is actually equivalent to 3 volts it's the same thing so all the voltage is going to be dropped we will see it across this this load now if you want to do it maybe well put the probe in the um opposite way so let's say we want to say this is the negative and this is the positive and this is let's call this v2 same thing it's just uh instead of so here what we have we have the positive is with the negative and the negative with the positive so just like we're seeing it was going to be the same potential 3 volts but in this case since they are opposite um the the way we are uh putting the probe in so we're going to see the negative 3 volts so then in this case then v2 is negative three volts so that's that's um that's how we will measure the voltage it can be positive can be negative it depends how we are putting the probe to read it so that that's for the powers of life all right let's um let's see um if we uh have so the so we usually assume that the voltage source can supply as much current as we need to or as needed so [Music] let me look at this so we assume a voltage source can supply as much current as we need so in this case if we look at this example here again we have the power supply it's a circle symbol positive negative and let's say it is five volts and then we're connecting it to some load designate as a box empty box and so obviously the current is going to flow out of the positive uh terminal so it's going to flow in this direction i so that is the current so the current like we said it it will be as much as we will usually need it depends of course on the load that we are putting um across um so it can be uh if of course if the current is becomes too large if we're drawing too much current out of this voltage supply it might make it less than 5 volt if we drawing too much out of it but usually if we um draw within the range of this water supply then the current then will depend on whatever the circuit is needing so the current here is going to be um based on whatever the circuit needs if it happens that we are drawing too much current the voltage may not be it's not able to supply all of that current and hence we will see that its value may be less than 5 volts could be 4.5 or or 4 volts and so forth so um it we we have to draw what the voltage supply can eventually uh uh provide so that that's the in the in the practical um sense so the current supply have as high of potential of voltage potential as needed so a current really source it is not a common um element to have or it's not common component to have but um it it can be of course uh needed in that sense we can say we want to buy and we can buy um a current supply let's send and i want to supply 1 amp 2 amps 10 milliamps whatever that we want to supply to the circuit so it is usually it is possible to have it but it is not common to have a current supply we will usually have voltage supply all right so then we talked about the we said two types of uh sources and we said they are the independent the second one and we talked about the independent now the second one is the dependent dependent uh power supplies and with dependent power supply what does it mean it means that the the source depends on another circuit element so that's what it will usually uh means it depends on another circuit element okay so the so then the value in this case of this power supply value depends of this power supply depends on another a circuit element and we will do an example to see that so one of them and the symbol we will usually draw for dependent power supply is the diamond shaped so that's when you see a diamond the it is it means that it is a dependent uh power supply the voltage supply i mean independent they are circle or just for the battery in that case we just have like the two um plates uh one larger than the other to designate positive negative terminal for the um battery so in this one here we will have and the same thing we will have a positive or negative so that is a terminal this is another the other terminal and since i put bypass the negative means that we have a voltage uh source and this voltage source can depend on another element so let's say k k is like a constant that can be any value and then let's say the x so this k v x i should rather draw it next to it so k v x just k is just a value a constant value and v x is just another source so we'll say this voltage source so this is a voltage source that depends on the value of x so it's a voltage source um voltage dependent we can we will use designated as that voltage source voltage dependent means that depends on the value in this case of vx which could be somewhere in the circuit that we are maybe we are looking at or we are examining another so this is one of them another one it can be a voltage source but maybe a current dependent so it's it's somewhere depends on a current going through a circuit element so if you want to draw the same thing diamond shape yeah this is so so here we will say this is a voltage source and so i draw the positive and negative terminal within this source so this is a voltage source and then whatever i put next to it that designate whatever what does it depend on in this case if i put k i x it means that it is dependent on a current somewhere and in the circuit that is called i x so this is voltage source current dependent so this is a voltage source current dependent in this case depend on the value of ix another one another diamond shaped and if i drew an arrow inside of it it means that this is the a current source so it so what is this one this is a current source and now it depends maybe on another current so we can say this is k i x so this is our current source current dependent so it depends on i x again k is just a constant value the last one that we will we might encounter with dependent sources again a diamond shape which means that it is a dependent source and since i put the error so this is a current source and that it can depend on um in this case voltage source so that's k and maybe we have vx so then this is a current source voltage dependent so it depends on voltage somewhere else in the circuit so these are the four different dependent sources we might encounter either voltage source that depends on a voltage element somewhere in the circuit or depends on a current somewhere in the circuit we have a current source that depends on a current in the circuit or can depend on the voltage so these are the four different ways we might have now you might ask do we really encounter these dependent sources are they in practical term we can encounter them yes um usually most of the time we will encounter them by for example in um and transistors so transistors are or behave as dependent sources you're not going to encounter this transistors and in this course but you will in the electronics uh classes you will see that um transistors you will see a lot of that uh in those so that that can then occur in uh some circuits like uh transistors so that's where we'll see a lot of these uh dependent uh sources all right let's let's um let's do another example on this to show how we use the dependent source so we have as an example let's say we have this circuit that i'm going to draw given circuit below we have um this is a voltage source since i drove it like that and its value is 9 volts and it is connected to another element can be a resistor or any element you can call it a load or whatever so that is connected in that fashion so this is and this one here we designate the voltage across of it is vx and then this is continuing this is usually your encounter something like that and electronics like transistors this is how we model the circuit for a transistor something like that so and this is here we can see this is a dependent source and it is voltage source and it depends on a voltage element vx and so it is its value is the 3vx so see it depends on vx it's a voltage source that depends on the x which we have in this under this element here in this circuit and then it is connected also to a load um calling this so this is a positive negative and we call this vl and we have the current here that is flowing out of this dependent voltage source call this i so this is what is um given and the and of course in the questions we have uh for it we want to find what is the value of vl and then want to ask what is the power across the load case vl if the current i is two milliamps so now the current then is given to us as two milli amps so that we can right next to it here two milliamps since that it is now provided to us okay so now we want to find so when you what is uh what is it we are looking for we're looking for we want to find from this first question we want to find vl so when we look at vl it is in parallel across this here but we have this dependent voltage supply so that is here we see the positive of the positive terminal negative with the negative so it is a parallel in parallel so it is the value is going to be the same thing as whatever that value of 3x vx so so then v l we see is equivalent to 3 v x and what is the value of vx so here we were kind of like looking at this part of the circle i mean the circuit like that so that's when we find vl so this is like another part so this is how it is connected just through this wire and like this is you will see like i said a lot and when you're doing electronics transistors and so forth that's when you see circuits like that um now the uh we will see now vl we said is 3vx but what's what then we need to know what's the value of vx we don't know the value of vx so we need to look at the circuit this is where vx is and hence we will now we need to find what's the value of v x we see that in this part of the circuit that v x is in parallel with the power supply the nine volts power supply so it is the same thing so this is the positive this is the negative the positive potential to the positive potential negative with the negative so that's in parallel so then we will see that all the nine volts are going to go across it's going to be seen across this vx so then in this case vx is equivalent to um 9 volts so then since that is the case then vl is 3 times the x we said is 9 volts so times 9 so that is going to be 27 volts so then that is the answer to the first value now if we want to find the power of the second question the power across the load here so that is the power across here what's the power is going to be v times the current so the power is equal to the current and the current i is provided to us times the voltage across the load right so so in this case the current is provided to us as two milliamps and then multiplied by vl which we just found which is the 27 volts and multiplying the two that's 2 27 that's 54. and since this is milli and this is also that's going to be milliwatts so that's 54 milliwatts so now the question we want to ask is this um supplying voltage is it the power is supplied or is it absorbed of course any any time you will see that since this is a positive value anytime we have positive it means that it is going to be absorbing power so this is an absorbing power since it is positive so always uh positive if the value we we calculated is positive it means that it is absorbing power if it is a negative it is delivering power or supplying power okay so then can uh power supply absorb power can we have a parcel because here we were saying what is the power across can we can can a power supply absorb part of course we're talking about power supply and that that might kind of like being tricky or confusing because we're saying power supply but at the same time we're saying cannot be observed it's just it's just a name we're using the name power so we can just say the power supply so can the power supply absorb that's just a question power is there situations in which we have that do you think yes we do there situation in which we have batteries in which they are rechargeable when they are the batteries and when we use them they are supplying power and then when they run out and then we recharge now they are absorbing power so that's that's the case when we will have um that's an example of having a power supply absorbing power and that is the case when we have a rechargeable battery so a recharging power supply can have that just like your um your cell phone when you use it when it's the battery is full it is supplying power and then when you run out and you put it to recharge it you um you're charging it um your cell phone you're charging your phone you're recharging the battery in this case the uh battery now is um absorbing uh the power okay so so that is the uh case so we can say always if um as as a norm if power computed is positive then it is absorbing always it is absorbing power or consuming power if power computed is negative then we will say it is supplying or delivering power so that's always the case all right that's it for this video and thank you for listening