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there's one more thing we need to do now
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before we begin to solve electric
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circuits we need to define what is an
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electric circuit and what are the
0:21
components of a circuit that's what
0:23
we'll do in this clip and then we will
0:26
begin to solve electric circuits the
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electric circuit is a pathway for
0:32
charges to flow and there are three
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components you need a power source or a
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voltage source some kind of electric
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device and a switch let's look at each
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in turn for the voltage source we use a
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battery now this is the symbol here that
0:55
we use and this represents actually the
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first one here a cell when you have a
1:02
single cell that's the symbol when you
1:05
put several of these together you have
1:07
what they call a battery will use either
1:10
in our practice problems now notice that
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the longer side will be positive and the
1:17
smaller side is negative so here's the
1:20
positive and the negative and the
1:23
current only flows in one direction when
1:26
we use a battery and so it's called DC
1:30
current or direct current all of that
1:34
must be memorized now the battery
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supplies a potential difference and as
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I've said before this is often called an
1:41
electromotive force or an EMF and it's
1:46
given the symbol E as shown now the
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problem is it sounds like then potential
1:52
difference is a force but it isn't now
1:54
sometimes it is helpful to think of it
1:57
as a force like quantity that pushes
2:00
charge you know through the wire but it
2:03
is not a force now next we need an
2:07
electrical device now I've already
2:11
mentioned before that this converts
2:13
electrical energy to other forms of
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energy now what do we mean by this well
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you might use a light might be in the
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circuit as the electrical device maybe
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you'll have some kind of a heater maybe
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you'll have mechanical energy I got a
2:31
motor or a buzzer making sound but what
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we do when we use these electrical
2:36
circuits we will use a resistor to
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represent these electric devices and
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that's the symbol for the resistance and
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it will stand for these devices finally
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we have the switch as shown here a
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switch and if it's open that means the
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path is broken and the charge will not
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flow now there are two kinds of circuits
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broadly speaking there's the series
3:04
circuit and that means there's only one
3:07
path for the charge to follow and the
3:11
path starts from the positive terminal
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we actually have from the positive
3:18
terminal always to the negative terminal
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and notice there's only one path for
3:23
that charge to follow now when we have
3:27
this flow of if you will positive charge
3:30
it's called conventional current if the
3:33
flow of positive charge now we know in
3:35
truth it's actually electrons that flow
3:37
but for historical reasons we use the
3:40
flow of positive charge everything works
3:42
out fine and this is what most
3:44
university textbooks use and a parallel
3:47
circuit has more than one path the
3:51
current again flows from the positive
3:54
terminal comes to the junction splits up
3:58
goes through different paths there's
4:00
more than one path to follow and then it
4:03
comes back to another Junction and then
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it'll flow back to the negative terminal
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a parallel circuit has more than one
4:11
path for the current to flow
4:17
so you need to know the definition of an
4:20
electric circuit a path for charges to
4:23
follow DC current flows in one direction
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only conventional current flows from
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positive to negative flow of positive
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charge a series circuit only one path
4:37
for the charge parallel circuit more
4:40
than one path for the charge
