- In this video, we're going to talk about
some terminology that we use to talk about
how circuits are put together.
In previous videos, we've talked about
the components or elements that are used
to make up circuits, so for example,
resistor, capacitor, and inductor
are circuit components, we also call those elements.
In addition, we have some sources
like a voltage source or for example, a current source.
Those would be the components
or elements of a circuit, el-e-ments.
Now we're going to start assembling these things
into circuits, and we need a few more words to talk about.
Here's some circuit components that are laying
out on the tabletop,
and we're going to connect those up with a wire.
For example, I could connect this one to this one
with this yellow ideal wire, and an ideal
wire has zero resistance and is perfect everywhere,
and this forms a junction between these two components
and that is called a node.
Node is the word for junction, meaning the same thing.
And that's what a node is.
If I connect up these two other components,
I still have one node because I have one junction
that's the same voltage everywhere,
so that's what a node is.
We're going to go over to this circuit here
and we'll identify the nodes.
This is a little more normal-looking, tidy circuit.
Here's a junction right here between
a resistor and this voltage source,
so that's one node.
If I move over here, I see resistors
connected together by ideal wires,
so that forms one single node like that.
So that's our second node, and down below,
same sort of thing, I see an ideal wire
connecting the resistors and the source.
So I can color that in and that's
node number three.
So this circuit has three nodes.
Now what's connecting the nodes?
The thing that's connecting the nodes is called a branch.
And a branch is the same thing as an element.
We'll cap the... the branches are elements in this thing.
This voltage source connects the third node
to the first node, so that's one element.
This resistor connects node one and node two,
so that's the second branch.
This resistor connects node two and node three,
so there's the third branch, and this resistor
with a separate current also connects those two nodes
so that's the fourth branch.
So this circuit has one, two, three, four
elements in it, and it also means it has four branches.
Four branches, so that's what a branch and a node are.
I can move the picture over a little bit
so that we can do this again on
a little more fancy circuit.
So the first thing we're going to do again
just to repeat the process, we're going to count the nodes.
Here's a junction between a resistor
and a source, here's three resistors
connected by a perfect wire.
So that's the second node.
Here's three more resistors, connected
by a perfect wire, there's a third.
Down here we have, there's a junction
between two resistors, so that's our fourth node.
And finally we have this node here
connecting these four elements
with one node.
This is sometimes called a distributed,
a distributed node when it's all spread out
on the page like that, but it's still just one node.
So this circuit has five nodes.
And if we count up the elements,
that will tell us how many branches there are.
One element, two, three, four,
five, six, seven.
Seven elements.
All right, there's our two, two key words.
Elements and nodes.
Now I'm going to quickly move again
down, bring in another circuit here.
Now we're going to talk about the idea of a mesh.
And the other thing we're going to talk about
is the word loop.
The word mesh comes from screen doors
or screens that you put on your windows
to keep the bugs out.
If I draw a screen like this, this is what
it looks like, a bunch of crossing wires
and this little space right here, that little gap
is called a mesh, that's what that word comes from.
So we're going to find the meshes of our circuit,
and what we look for, here's the branches,
and the mesh, it is a kind of a loop
that fills up this open space.
This circuit has one mesh,
two mesh, three meshes.
That's how that looks.
To draw a mesh, you start on a node,
you go through elements until you come back
to where you started.
That's how we did those three,
and they fill the open windows of the circuit.
So this circuit has three meshes.
Now a mesh is a loop, and we can have
other kinds of loops too.
They don't have to be just the ones
that fill the windows, so in general,
this circuit has other loops, and we'll identify
some of those, let's just start at one of these nodes here,
and go around like that and this is a loop.
And I could draw other loops in here.
We'll make them all different colors.
There's a loop if I start right here,
I can draw a loop through these elements.
And finally, if I have a sharp eye,
there's one more loop in this circuit.
Let's just start right here, and it actually
goes all the way around the outside.
So this circuit has three, actually,
if I add them together, this has three loops
that I drew here plus the three loops
that were the meshes, so this circuit has six loops.
Circuits always have a lot of loops,
and so usually we don't talk about these.
More often, it's more organized and straightforward
to talk about how many meshes are in a circuit.
All right, so that does it for this video.
We got mesh and loop, we talked
about components and elements.
And we finished up with the idea
also of nodes
and branches.
So that'll do it, there's our new vocabulary
for talking about circuits.