0:11

So, let's talk a little bit about basic property properties of electrical

Â circuits.

Â Start with voltage.

Â So, we got our circuit on the right, on the left side it's green rather.

Â And to the circuit in this case has got a battery on the left.

Â On the right, it's got that squiggly line there, it's called a resistor, and

Â we'll talk about that in a few slides,

Â but a resistor basically provides resistance to the current flow.

Â So, that could be a number of things, and

Â we'll talk about that in a couple of slides.

Â But that's our circuit.

Â And current's flowing from the positive through that resistor to the negative.

Â 0:41

Now, on the other side over there next to it, we have the water,

Â the analogous water circuit.

Â Now, the water, they've got a pump, it's pushing water, and

Â notice that I put some rocks inside the pipe.

Â So, these rocks are providing resistance to the water flow.

Â So there, I'm gonna call those resistance.

Â Those are similar to the resistance inside the,

Â to the resistor inside the electrical circuit.

Â 1:03

So, this concept of voltage,

Â voltage is called the potential difference between two points in the circuit.

Â So, what this means, potential difference is, think of voltage as the pressure.

Â So, voltage is just like the pressure in the water system.

Â That pump provides pressure on the water that you can measure with, say,

Â a pressure gauge, right?

Â But note that, pressure is what actually pushes the water through.

Â So voltage, that battery in our picture is actually providing some voltage.

Â Providing essentially the pressure on the carriers on the electrons to

Â push them through the circuit.

Â So, think of voltage like that.

Â Now note that, pressure difference is what counts.

Â So, what I mean is.

Â There's pressure but current only flows if there's a difference in voltage.

Â Like in water.

Â It's like water.

Â Just start with water.

Â Let's say, you got a pipe.

Â There's two ends of the pipe, right.

Â Water flowing through, but there's two ends of the pipe.

Â And both of them,

Â there's a high pressure you put, it's a powerful pump on one end, right?

Â So, the high pressure there.

Â You put a powerful pump on the other end, same pressure.

Â So, there's high pressure on the other end.

Â How much current is flowing?

Â If they're equal pumps with equal pressure, then there's no current flowing,

Â even though, you've got high pressure on one end, high pressure on the other.

Â The pressure different between the two end points of the pipe,

Â there's no difference in their pressure.

Â So, there's no flaw.

Â So, even though, there's high pressure, the pressure difference is what counts.

Â And voltage is the same way.

Â There has to be a difference in voltage, and that's a different thing.

Â That you put that out, what they call potential difference,

Â difference in Potential.

Â So, between the positive and negative terminals of the battery,

Â you have a potential difference of whatever amount of voltage the battery is.

Â So say, that battery is rated at five volts, then that means, there's five volts

Â potential difference between the positive and negative terminals.

Â Which means, that if you wire those two together,

Â current will flow from the positive to the negative.

Â 2:53

So, it's measured in volts.

Â And I should note that the voltage on anything that is connected by a wire, like

Â just a plain wire, positively conductive wire, they have the same voltage, right.

Â There's no resistance in between.

Â Of course, in our circle we have resistance in between.

Â 3:12

Okay, so that's voltage.

Â Current, another important property of a circuit.

Â Current is what you think of it as,

Â is the rate at which the carrier flows past the point in the circuit, okay.

Â So, if you look at the water, the rate at which water is flowing past the point in

Â the circuit, you call that the current flow or the current rate.

Â And you get the same thing In our electrical circuit.

Â Now, current flows from positive to negative.

Â That is the standard.

Â That is what people say.

Â Now, that's not exactly what happens.

Â So, in current,

Â with electrical current our carriers are actually electrons, right?

Â And that, well we don't need to know this for the class, but

Â I should throw this in because sometimes it's confusing.

Â But, understand that electrons are negatively charged characters.

Â So, they don't actually flow from positive to negative,

Â they flow from negative to positive.

Â So, even though, we say that current flows from positive to negative,

Â 4:03

in reality the electrons are flowing from negative to positive.

Â Okay?

Â Just be aware of that.

Â But still, when people talk about current flow, they always say oh its going from

Â positive to negative so always think of it that way.

Â I just wanted to mention it to you, because sometimes,

Â if you know anything about electrons, then it can be a contradiction in your head.

Â So, that's there, but

Â just understand that everybody says positive to negative current flow.

Â They're talking about the holes, the lack of electrons is moving

Â from positive to negative, you can think about it like that.

Â 4:42

All right, resistance.

Â So, resistance is basically and obstacle to current flow.

Â So, in terms of our water system, I put some rocks in the pipe and

Â that's a resistor effectively.

Â It's providing resistance.

Â It's slowing the water flow and reducing the rate, right?

Â So, that's resistance.

Â There are a lot resistance you can put in there.

Â You could put a sponge in there, right?

Â And that would, you know, water could flow past it.

Â But it would be, it was hard to flow past it.

Â So, that's a resistor.

Â Now, for us, in an electrical circuit.

Â 5:10

So, for water, just a rock or a narrow pipe.

Â If you make the pipe narrow, that adds resistance, right?

Â It makes, it's harder to push,

Â though pumped to a very narrow pipe, as compared to a big wide pipe.

Â So for water, that could be the case.

Â For a circuit, it's basically a bad conductor [LAUGH], okay?

Â A sub-optimal conductor.

Â So, if you just have pure copper wire, there's very little resistance in there,

Â it's very good for conducting.

Â But, if you use some other material that doesn't conduct as well,

Â then it has a certain level of resistance.

Â Now then, you can go to an extreme and use an insulator,

Â just something with extremely high resistance, like the air, right?

Â Regular air, at regular humidity levels, it's an insulator, right?

Â It has a very high resistance between any two points in the air.

Â So, but there's a gradation, right?

Â You can different types of materials that have different levels of resistance

Â per unit length.

Â 6:00

Also a narrow conductor.

Â The narrower the conductor is, the more resistance there is.

Â So, if you take a wire, you have a big fat wire,

Â that's less resistance than if you have a really thin wire.

Â And actually, this is important with high power electronics.

Â You have to use big fat wires because there's so

Â much current the resistance will produce a lot of heat, so you need big wires to

Â drive a lot of current or else you'll get too much resistance.

Â So, that's what resistance is.

Â So, we've got voltage, current, and resistance are simple ideas and

Â principles, it's different aspects of electrical circuits that we need to

Â be aware of a little bit.

Â And resistance is measured in Ohms.

Â Thank you. [MUSIC]

Â