 Let's explore the idea of potential difference. Potential difference between any two points in a circuit is basically the energy gained or lost per coulomb. So it's basically energy gained or lost per charge and so its units becomes joules per coulomb which we call volt. Let's take an example and we'll make things clear. So we have a circuit over here. Let's say we say that the potential energy of the battery is 10 volt. What does that mean? Well it means that when charges move across the battery, they gain energy, right? So the 10 volt is saying that the charges gain 10 joules of energy per coulomb. So every coulomb that moves across the battery gains 10 joules of energy from the battery. That's all it means. So if you have two coulombs going by, it would gain 20 joules of energy and so on and so forth. Now what happens to that energy that the charges gained? Well as it goes through the circuit, when it goes through an appliance, it dumps all of that energy, transfer that energy to the appliance which means as charges go across this bulb, they lose that 10 joules of energy. So every coulomb as it goes from here to here loses all of that 10 joules and so even here across these two points, we will say that there is a potential difference of 10 volt because the same thing is happening. Here it is gaining 10 joules. Every coulomb is gaining 10 joules and as it goes from here to here, it is losing 10 joules. Does that make sense? But what about let's say between these two points? Well the charges are not losing or gaining any energy between these two points. Now of course in a real circuit, of course the charges will lose energy because it gets converted to heat but if we ignore that, then there is absolutely no energy gained or lost and therefore the potential difference between these two points is zero. There is no potential difference between these two points. So between these two points, we have zero volt potential difference and same is the case between these two points. There is zero volt potential difference because there is no energy gained or lost by the charge. Now can you think about what would it mean if you had a battery which had a 100 volt? Well it just means that that battery transfers 100 joules of energy per coulomb. Makes sense right? That's all what potential difference is. Now let's do a couple of more examples. So here's the first example. It's given that five coulombs of charges move through the battery and the battery does work of 20 joules on them. What is the potential difference across the battery? How do we figure this out? Well can you pause and try yourself first? All right. We know that potential difference is energy gained per coulomb. So per charge. Now it's given that the battery does 20 joules of work. Remember when you do work, you transfer energy. So since battery did 20 joules of work on these charges, these charges gained 20 joules of energy. Even though it's not mentioned directly, work does represent how much is energy gained or lost and so the energy gained in this case is 20 joules. It really doesn't matter whether it gained or lost. All that matters is how much that energy is per coulomb. So per five coulomb and so that gives us four joules per coulomb which is four volt. So the potential difference between these two points is four volts. Okay let's try the other one. We have given that the potential difference across a bulb is seven volt. Now if two coulombs of charges pass through it, the question we need to figure out is how much energy is gained or lost by these charges? Can you pause and try to do this yourself? Okay. This time we're given the voltage which is the same thing as potential difference and the charge is given to us. Two coulombs is flowing. So we need to find what the energy transferred or energy gained or lost is. So if we rearrange the equation, what is equal to? Well we can multiply by q on both sides. So we'll get equals v times q. That gives us seven, seven volt times two, giving us 14 joules. So 14 joules of energy was transferred. We know that the 14 joules of energy must have been lost by these charges and you can even directly think and do it without the formula. Seven volt represents seven joules per coulomb. It means that one coulomb lost seven joules of energy. So two coulombs would have lost 14 joules of energy. So you could have directly done it as well.