Alright this will be your crash course into electricity and DC circuits aiming to get
Alright this will be your crash course into electricity and DC circuits aiming to get

you ready for Physics Olympics and to introduce you to these concepts that we'll then see
you ready for Physics Olympics and to introduce you to these concepts that we'll then see

later in the year.
later in the year.

when we start off thinking about electricity, one of the really common metaphors we use
when we start off thinking about electricity, one of the really common metaphors we use

is to compare an electrical circuit to a river.
is to compare an electrical circuit to a river.

And in that analogy, the current the electricity that's flowing is the amount of water that
And in that analogy, the current the electricity that's flowing is the amount of water that

we have in the river.
we have in the river.

Current in an electrical circuit is a lot like current in a river.
Current in an electrical circuit is a lot like current in a river.

The electrons are like the drops of water and one stream of current or one stream of
The electrons are like the drops of water and one stream of current or one stream of

electricity is made up of many many many many electrons or many many drops of water.
electricity is made up of many many many many electrons or many many drops of water.

Electricity is simply equal to the flow of electrons, which you probably already knew.
Electricity is simply equal to the flow of electrons, which you probably already knew.

In order for there to be a flow of electrons, they have to have some place where they can
In order for there to be a flow of electrons, they have to have some place where they can

flow and that's what we call a circuit.
flow and that's what we call a circuit.

And that's what we're going to talk about now.
And that's what we're going to talk about now.

On page 731 in your Holt Physics book, you'll find a table that shows you the basic diagram
On page 731 in your Holt Physics book, you'll find a table that shows you the basic diagram

symbols used in schematics.
symbols used in schematics.

So the first one you should be familiar with is the wire.
So the first one you should be familiar with is the wire.

And this is just the path in which electricity flows through the circuit.
And this is just the path in which electricity flows through the circuit.

it's given by a straight black line and that line can bend or twist or go in any number
it's given by a straight black line and that line can bend or twist or go in any number

of directions.
of directions.

but when you see a single line given in a schematic diagram, that's a wire.
but when you see a single line given in a schematic diagram, that's a wire.

the next symbol you'll need to know that is really important is the symbol for a resistor.
the next symbol you'll need to know that is really important is the symbol for a resistor.

There are two symbols commonly used, the one that I've drawn here is the one that we'll
There are two symbols commonly used, the one that I've drawn here is the one that we'll

be using.
be using.

the next symbol you'll need to know is that for a bulb, if you notice that the symbol
the next symbol you'll need to know is that for a bulb, if you notice that the symbol

for a bulb looks a lot like a tiny resistor inside a globe.
for a bulb looks a lot like a tiny resistor inside a globe.

there's a reason for that.
there's a reason for that.

Light bulbs in a circuit create resistance.
Light bulbs in a circuit create resistance.

The symbol for plug is one that we will not be using in this breif unit.
The symbol for plug is one that we will not be using in this breif unit.

Because plugs are a feature of AC circuit,or an alternating current circuit.
Because plugs are a feature of AC circuit,or an alternating current circuit.

We'll only be dealing with direct current circuits.
We'll only be dealing with direct current circuits.

So, no plugs for us :( A symbol we will use frequently is the symbol for a battery.
So, no plugs for us :( A symbol we will use frequently is the symbol for a battery.

This is a battery for a single cell, while this one is a battery with multiple cells.
This is a battery for a single cell, while this one is a battery with multiple cells.

This is the place where the electrons are going to flow from and return to.
This is the place where the electrons are going to flow from and return to.

The symbol for a switch can be shown 2 ways.
The symbol for a switch can be shown 2 ways.

The first way shown here is the open position.
The first way shown here is the open position.

While the second one is in the closed position.
While the second one is in the closed position.

when the switch is open on a circuit, electrons cannot flow and therefor there's no current
when the switch is open on a circuit, electrons cannot flow and therefor there's no current

flowing through the circuit.
flowing through the circuit.

A switch is turned on when it is in the closed position, and electrons can flow through the
A switch is turned on when it is in the closed position, and electrons can flow through the

entire circuit.
entire circuit.

A capacitor is our final symbol, is a device used for storing current.
A capacitor is our final symbol, is a device used for storing current.

And a capacitor is actually a structure made out of two plates of material that are set
And a capacitor is actually a structure made out of two plates of material that are set

parallel to each other.
parallel to each other.

This is a standard capacitor notation, while this is one that can only be used on a direct
This is a standard capacitor notation, while this is one that can only be used on a direct

circuit and the polarity has to line up at that battery.
circuit and the polarity has to line up at that battery.

Notice that the symbol for a capacitor bears some resemblance to a battery.Battery's store
Notice that the symbol for a capacitor bears some resemblance to a battery.Battery's store

current, they store electrons or charge, so does a capacitor.
current, they store electrons or charge, so does a capacitor.

This is a schematic pf a very simplified direct current circuit.
This is a schematic pf a very simplified direct current circuit.

We have a battery located here.
We have a battery located here.

And a charge will flow from the area of high potential to the areas of low potential.
And a charge will flow from the area of high potential to the areas of low potential.

right now, however, no charge can flow because this switch is open.
right now, however, no charge can flow because this switch is open.

If we want charge to flow we have to do something.
If we want charge to flow we have to do something.

That's better, now charge can flow from the area of positive potential through that switch
That's better, now charge can flow from the area of positive potential through that switch

because it's closed now, through the bulb, and back to the area of low potential, completing
because it's closed now, through the bulb, and back to the area of low potential, completing

the circuit.
the circuit.

the other part of the circuit that I hope you noticed was the light bulb.
the other part of the circuit that I hope you noticed was the light bulb.

why does the light bulb light up when charge flows through it?
why does the light bulb light up when charge flows through it?

When current flows into the light bulb, remember that we said that center part of the light
When current flows into the light bulb, remember that we said that center part of the light

bulb is a lot like a resistor, it's an area of high resistance to the flow of electrons
bulb is a lot like a resistor, it's an area of high resistance to the flow of electrons

within that piece of wire.
within that piece of wire.

Because it's got such high resistance, it generates heat.
Because it's got such high resistance, it generates heat.

And you have heat and light coming off the light bulb hence, it glows!
And you have heat and light coming off the light bulb hence, it glows!

SO the big primary thing to remember about circuits is...any circuit in order to work
SO the big primary thing to remember about circuits is...any circuit in order to work

must have a source of potential difference, and it must have a complete and continuous
must have a source of potential difference, and it must have a complete and continuous

path back to the other side of that source of potential difference.
path back to the other side of that source of potential difference.

Any source that does not have those elements will not conduct.
Any source that does not have those elements will not conduct.

Here's your first quiz question!
Here's your first quiz question!

Write it down on a piece of paper, it's due when you walk in tomorrow.
Write it down on a piece of paper, it's due when you walk in tomorrow.

Which of the diagrams below shows a circuit that will conduct current?
Which of the diagrams below shows a circuit that will conduct current?

Okay, let's talk briefly about resistance.
Okay, let's talk briefly about resistance.

Resistance is just the opposite of the movement of charge through the material.
Resistance is just the opposite of the movement of charge through the material.

think of it like friction inside a wire or inside some other material where flow or current
think of it like friction inside a wire or inside some other material where flow or current

is attempting to flow.
is attempting to flow.

Any circuit, no matter what material it's made of, whether it's copper or gold or anything
Any circuit, no matter what material it's made of, whether it's copper or gold or anything

else we'll have some native resitance wire itself will.
else we'll have some native resitance wire itself will.