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
later in the year.
when we start off thinking about electricity, one of the really common metaphors we use
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
we have in the 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
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.
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.
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
symbols used in schematics.
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.
it's given by a straight black line and that line can bend or twist or go in any number
of directions.
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.
There are two symbols commonly used, the one that I've drawn here is the one that we'll
be using.
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.
there's a reason for that.
Light bulbs in a circuit create resistance.
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.
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.
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.
The symbol for a switch can be shown 2 ways.
The first way shown here is the open 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
flowing through the circuit.
A switch is turned on when it is in the closed position, and electrons can flow through the
entire circuit.
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
parallel to each other.
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.
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.
This is a schematic pf a very simplified direct current circuit.
We have a battery located here.
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.
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
because it's closed now, through the bulb, and back to the area of low potential, completing
the circuit.
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?
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
within that piece of wire.
Because it's got such high resistance, it generates heat.
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
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.
Any source that does not have those elements will not conduct.
Here's your first quiz question!
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?
Okay, let's talk briefly about resistance.
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
is attempting to flow.
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.