0:11

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

circuits.

Start with voltage.

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

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

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

we'll talk about that in a few slides,

but a resistor basically provides resistance to the current flow.

So, that could be a number of things, and

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

But that's our circuit.

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

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

the analogous water circuit.

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

notice that I put some rocks inside the pipe.

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

So there, I'm gonna call those resistance.

Those are similar to the resistance inside the,

to the resistor inside the electrical circuit.

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So, this concept of voltage,

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

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

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

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

a pressure gauge, right?

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

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

Providing essentially the pressure on the carriers on the electrons to

push them through the circuit.

So, think of voltage like that.

Now note that, pressure difference is what counts.

So, what I mean is.

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

Like in water.

It's like water.

Just start with water.

Let's say, you got a pipe.

There's two ends of the pipe, right.

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

And both of them,

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

So, the high pressure there.

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

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

How much current is flowing?

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

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

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

there's no difference in their pressure.

So, there's no flaw.

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

And voltage is the same way.

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

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

difference in Potential.

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

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

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

potential difference between the positive and negative terminals.

Which means, that if you wire those two together,

current will flow from the positive to the negative.

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So, it's measured in volts.

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

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

There's no resistance in between.

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

3:12

Okay, so that's voltage.

Current, another important property of a circuit.

Current is what you think of it as,

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

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

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

And you get the same thing In our electrical circuit.

Now, current flows from positive to negative.

That is the standard.

That is what people say.

Now, that's not exactly what happens.

So, in current,

with electrical current our carriers are actually electrons, right?

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

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

But, understand that electrons are negatively charged characters.

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

they flow from negative to positive.

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

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in reality the electrons are flowing from negative to positive.

Okay?

Just be aware of that.

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

positive to negative so always think of it that way.

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

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

So, that's there, but

just understand that everybody says positive to negative current flow.

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

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

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All right, resistance.

So, resistance is basically and obstacle to current flow.

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

that's a resistor effectively.

It's providing resistance.

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

So, that's resistance.

There are a lot resistance you can put in there.

You could put a sponge in there, right?

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

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

So, that's a resistor.

Now, for us, in an electrical circuit.

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

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

It makes, it's harder to push,

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

So for water, that could be the case.

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

A sub-optimal conductor.

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

it's very good for conducting.

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

then it has a certain level of resistance.

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

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

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

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

So, but there's a gradation, right?

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

per unit length.

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Also a narrow conductor.

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

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

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

And actually, this is important with high power electronics.

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

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

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

So, that's what resistance is.

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

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

be aware of a little bit.

And resistance is measured in Ohms.

Thank you. [MUSIC]