L1 3B series and parallel

ECE1250 University of Utah. How to tell if circuits are in series and parallel (color code method)

In our last video we stopped, we talked
about color coding your nodes, and

color coding a node starting at one point,
one element, and moving all the way,

filling in the color to the next element.

Now, let's actually use that.

So here is a circuit diagram.

We show a battery,
an ammeter connected to a resistor so

that we can measure the current, might
watch measure the current in this circuit.

And here is the voltmeter measuring
the voltage across that battery.

That's a picture of what the circuit
would look like if we built it, but

down here is the circuit representation.

I'm going to show you how to color code
the nodes, so let's start with the red

node going from here all the way through
our ammeter and over to our resister.

I want to make a note that if
you are using ammeters and

voltmeters in your circuit,
basically ignore them.

You draw your line through the ammeter,
and you ignore or

just kind of remove the voltmeter.

So there's one node.

Here is another node.

Okay.

Now there's an important
feature of these nodes.

The voltage along the black is
the same every place on that node and

the voltage on the red is the same
every place on this node.

That's how nodes work.

Now let's use that idea to define
things that are in series and parallel.

When I fill in my node like this,
There is one part of my battery node,

here is another node and
here is one more node.

Are those nodes ordinary or extraordinary?

They're all ordinary, because they
only have two wires, not three.

So let's see how we can tell
when something is in series.

If, two elements share one color such
as these two, they are in series.

So bulb number one is in
series with bulb number two.

How about bulb number two and the battery?

It shares only this black line, so bulb
number two is in series with the battery.

How about bulb number one and the battery?

Well, they only share one color, so the
battery and this bulb are also in series.

In fact, all of the elements
in this circuit are in series.

Now let's look at a contrasting circuit.

This is the parallel circuit.

So fill in our node,
color coding it like so.

All the voltage is the same.

Let's fill this one in, color coding it.

All right, we have two
extraordinary nodes, a red one and

a black one, in this circuit.

Now, if we want to know if
something is in parallel, any two

elements that share the same color,
such as red and black, are in parallel.

Well, this bulb is red and black and
this one is red and black, so

they are in parallel.

This bulb and the battery are both red and
black, red and black, so

they are also in parallel.

All the elements in this
circuit are in parallel.

Compared to this, compared to the other
one where they were all in series.

Now in a series circuit the current
is the same throughout the circuit.

So the current comes out of the battery,
goes through both bulbs and comes back.

And the current is
the same everywhere there.

Even if these bulbs are resistant,
the current is not used up in them.

The current moves through it and comes out
and it's the same current the whole way.

Remember that we color-coded these.

Here's the path for the current that's
moving along through the red node and

then it goes to the bulb into
the blue node through the next bulb.

And finally into the black node.

And we could tell that this circuit was in
series by noting there was only one color

between any of these elements and
low behold,

the currents are the same
throughout this circuit.

Now in a parallel circuit, the voltage
is the same throughout the circuit.

So remember this red node?

We said that voltage was the same
every place on the red, and

the voltage is the same
every place on the black.

And we said that if two elements
shared the same two colors,

they were in parallel,
red black, red black, red black.

This is a parallel circuit.

Now the voltage is the same.

What does that mean?

That means that if I hooked
up my voltmeter, right here.

And I connected my red lead right here.

And I connected my black lead right there,
oops, I need the black lead, come on.

I would measure the same
voltage from red to black here.

As I would from here and from here.

So the voltage is the same every
place in a parallel circuit.

Now let's take a look at
several of these circuits and

decide what's in series and parallel.

This circuit right here,
how many nodes does it have?

It has one ordinary node.

It has another ordinary node,
that's two ordinary nodes.

Here's a third ordinary node.

Four ordinary nodes and
finally five ordinary nodes.

All right,
let's see what's in series and parallel.

If two elements share one color,
they are in series.

So the battery is in series
with the first resistor.

The first resistor shares only one
color with the second, that's blue.

So R1 and R2 are in series.

So we can say R1 is in series with R2.

Well R2 and R3 only share brown.

They're also in series.

And R3 and R4 share only green,
they are in series, and

finally back to the battery.

So R1 is in series with R2, which is in
series with R3 and in series with R4.

This is a series circuit and
the current is constant throughout.

Now let's go over to our next circuit.

Out of the battery I'm going to fill in

all of the node until I get
to all of the elements.

There is my red node,
that's clearly an extraordinary node.

Let's fill in this.

Okay, there's a blue extraordinary node.

That's two extraordinary nodes and
finally.

Here is the third extraordinary node.

Okay, elements are in parallel if they
share the same two colors such as

red to blue, and red to blue.

R1 is in parallel with R2.

Similar, blue to black, blue to black,
R3 is in parallel with R4.

Okay, now how about this combination,
which was R1 in parallel with R2,

and this combination,
which was R3 in parallel with R4.

If I looked at this combination, I would
say that they share a single collar,

this blue right here, they are in series.

So I can say,
the parallel combination of R1 and

R2 is in series with the parallel
combination of R3 and R4.

Now let's look at this
more complicated circuit.

Right here, is that an ordinary node or
an extra ordinary node?

It's ordinary.

This one right here,
ordinary or extraordinary?

It's extraordinary.

There are more than two wires
coming out of this node.

And right here, how about this one?

That's an ordinary node.

There is another extraordinary node.

That's an extraordinary node.

And finally here's one more.

There's yet another extraordinary node.

Okay, let's see what's
in series in parallel.

Here are two resistors
that share one color.

So I can see that R2 is in series with R3.

Right here, I have two resistors
that share two colors so

they're blue to yellow.

So I can see that R4 is in parallel
with R5, let's go right here R2 plus R3.

Alright, now let's start
putting these in combinations.

So there's the parallel
combination of R4 and R5.

Here's the series combination of R2 and
R3.

Well I can see that the parallel
combination of R4 and

R5 is in series with R6 because
it shares only one color, yellow.

And I can see that this combination,
that I just described is in

parallel with a series combination with R2
and R3 because they share blue and brown.

So this combination is in parallel with
this series combination of R2 and R3.

And finally, that whole combo,
Is in series or

parallel with R1, it's in series,
because they share only one color, blue.

This is what we'll be doing
throughout our circuits.

We'll practice it some today, and

we'll continue to practice it
throughout the next couple of weeks.

Here's a Wheatstone bridge.

Let's decide what's in
series in parallel here.

The way a Wheatstone bridge works is,
that we have an unknown resistance.

Typically a sensor right here.

Maybe it's a thermister that
changes with temperature and

we'd like to know what its resistance is.

The way we can do that is we can
take this variable resistor, and

we can change its resistance.

We can actually dial the resistance or

tune it, until this voltage
right here is equal to zero.

Then we know that the variable resistor
is equal to the unknown resistor.

Okay, let's decide what's in series and
parallel, in a Wheatstone bridge.

Here is one node.

Right there.

And here is a second node, right there.

What do I do about the voltmeter?

Remember, the voltmeter, I just remove,
just take it out of there.

It's as if it didn't
exist in this circuit.

Why doesn't it exist?

It's because the impedance
of a voltmeter or

the resistance of
a voltmeter is really high.

It's as if it was an open circuit,
so we treat it that way.

Okay, there's another node.

Right there and
finally here's one last node right there.

Okay, so what do I have?

I have two extraordinary nodes,
a red one and a black one,

and I have two ordinary nodes,
a blue one and a brown one.

Now let's see what we have for
our circuit.

Here I have two resistors
that share only one color.

R1 is in series with R2.

Here are two other resistors
that share one color.

Rv is in series with R unknown.

And if I consider these one group, and

these a different group, then I can see,
see there are my two groups?

I can see that this series combination
of of R1 and R2 is in parallel

because they share red and black with
the series combination of Rv and Ru.

So here is my set of resistors.

Now let's talk about series and
parallel battery charging and

the application of the idea of series and
parallel.