and if the pipe is small and has a very large flow resistance And a very small

flow. If I have the same situation with a much

larger pipe. Then the same pressure difference or the

same tensile difference is going to give you a much larger current or a much

larger flow. Okay, now that you've been introduced to

Ohm's law, to start building circuits we need one other thing.

We need a battery. So a battery is just a source of voltage.

And the representation of a battery is is this, showing the, the The cathode and

anode plates of the battery. The positive side of the battery is the

higher potential, this is lower potential side of the battery.

So a typical AA battery has a potential difference of about 1.5 volts between the

plus terminal and the minus terminal. So we can take that battery and we can

connect it with a resistor across it and a very simple circuit here.

So by this battery is going to establish a potential difference across the

resistor and a current's going to flow. And so the voltage across the resistor is

v. So using ohm's law, the current flowing

through the resistor, and that's also the same current has to flow through the

battery so that current is coming from the battery.

So the current coming from the battery flowing through the resistor is just v

over r Now this suggests a a method for solving a circuit like this, and what

this really is is a very simple illustration of Kirchoff's voltage law.

Kirchoff's voltage law says that the sum of the voltages going around a closed

path in a circuit Has to sum up to 0. So it's the sum of the voltage across

every element. If I add them all up and follow a closed

path, it's 0. So in this case, if I start at point A

and I go through the battery this direction, so I'm traversing the circuit

in the direction that I've defined. The current flow to be positive.

So I start at point a and I go through the battery from the low side to the high

side, and I picked up a voltage v and then I dropped a voltage r.

There's a voltage drop across the resistor.

I'm losing energy. And the sum of the VI pickup and the V

lost across the resistor has to be zero. So, you can think of this, really, as

kind of a roller coaster. So, if I start at some point in the

roller coaster and I follow the closed loop with ups and downs, I come back to

the same point And the change in my potential, I go up to a higher potential

energy and then and where I he, hit the top of the hill I have maximum potential

energy and I'm, I'm barely moving in the car and then the car goes down the, down

the hill and the potential energy's converted into kinetic energy.

But if I take and I keep track of how much potential energy I have at every

point going around this closed loop, when I come back, all of those gains when I go

up hills, and loses of potential energy when I go downhill, they all have to add

up to zero because after all I ended up back at the same point that I started at.