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so I hope you can see this one
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series-parallel
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you want to calculate R T given R 1 R 2
00:00:13
R 3 it's been parallel part series part
00:00:17
and here are our values here first step
00:00:21
to work out just the parent apart ignore
00:00:24
that part and just work out these two
00:00:27
so calculate parallel resistance total
00:00:33
of this bit here okay we'll call Rt
00:00:37
actually because it's part series
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parallel R 4 becomes 1 over 2 plus 1
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over 3 we put figures in
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like so these we can do when I cannot
00:01:05
glare can be done a lot easy I know
00:01:08
because the figures I've chosen the
00:01:12
button we press on our calculator is the
00:01:15
X to the minus one so what you want to
00:01:17
do is on your calculator 1350 press X to
00:01:21
the minus one button you press plus 50 X
00:01:25
the minus one equals and then X to the
00:01:29
minus 1 again to give you the correct
00:01:32
answer and if you do all of that it will
00:01:35
come to some of you probably hope you
00:01:37
already noticed should come to 25 hours
00:01:41
this happens to me guys because I've
00:01:43
chosen it that when you have the same in
00:01:45
parallel you just take one of them and
00:01:47
then find PI the number up so there's
00:01:49
over 50 there are two of them so 50
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divided by 2 is 25 again if we do the X
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to the minus 1 so that's 50 X minus 1
00:01:58
plus 50x on equals x the nice one your
00:02:03
answer that will give you 25 ohms that
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then breaks the circuit down so what
00:02:13
we've now got is this r4 which we now
00:02:19
know is 25 and r1 which was 25 as well
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so we've now broken this circuit down
00:02:29
into just a basic series circuit and we
00:02:32
can now find our T so our T becomes oh
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one plus r4 and r4 is this combination
00:02:41
here if we put these figures in so RT
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for the entire circuit it's 50 ohms and
00:02:58
that can again can be drawn simplified
00:03:00
into that entire circuit
00:03:08
as so we've started off as a series
00:03:11
parallel come to a series down to one
00:03:14
these are our three steps we've taken to
00:03:17
get to our final answer Artie okay now
00:03:23
we've made the circuit into three broken
00:03:27
down pieces effectively we know Artie is
00:03:30
50
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oh we now must do is calculate these
00:03:33
three currents this possibly makes it
00:03:37
easier to work these out this because
00:03:42
this is the total of the circuit from
00:03:45
previous the examples I T is equal to vs
00:03:53
divided by RT which is Ohm's law we put
00:03:57
these figures in 100 because this is the
00:04:01
total divided by RT just 50 is not
00:04:06
difficult to understand
00:04:10
two amps this two amps it would be the
00:04:13
same two amps that flows around in this
00:04:15
circuit here for a poorly it's this two
00:04:23
amps over here these two empty flows out
00:04:27
must come back so that's gonna to
00:04:29
amplify pass through the arm well I
00:04:32
guess at this point here it will split I
00:04:34
can split into i1 and i2 depending on
00:04:37
the value of these resistors will
00:04:39
determine which current how much current
00:04:42
goes each direction so how do we work
00:04:46
that one out
00:04:48
well to be honest there's not much to
00:04:50
work out this one because we know these
00:04:53
two are equal they're both fifty so
00:04:57
they're equal the current has to split
00:04:59
evenly therefore it will divide by two
00:05:02
so I already know and hopefully it will
00:05:04
recognize that every one and pass
00:05:06
through each one but if we need to work
00:05:09
it out we'd have to do a calculation so
00:05:13
we'd have to work out all right one
00:05:16
first hold a phone we use for that his
00:05:19
own law PV the
00:05:21
I did by ah the difference being now
00:05:25
though we want to calculate blackcurrant
00:05:28
so this step formed in this Holmes law
00:05:30
but it's wheat voltage do we apply
00:05:33
because what it isn't it isn't vs
00:05:35
because we yes is not across that
00:05:38
resistor and that's what we're trying to
00:05:40
find the current flowing through that
00:05:42
resistor there so in order to work that
00:05:45
one out
00:05:45
we've got to find the volt drop across
00:05:49
this resistor and that's easier to work
00:05:52
out from over here so to work this bolt
00:05:55
it help let's call it the one just to
00:05:59
really confuse matters to work out that
00:06:05
voltage there leave one trying to work
00:06:09
out it is Ohm's law r again I times ah
00:06:17
well looking at this circuit to find
00:06:20
that voltage there because this one is
00:06:23
all of that okay and we know from a
00:06:25
parallel circuit that voltage in a
00:06:27
parallel circuit will stay the same so
00:06:30
to work this one out it's the current
00:06:32
passes through that so this one here
00:06:34
it's two amps because it's a combination
00:06:36
of those two so becomes my teeth over
00:06:41
here times are four okay we know he's 25
00:06:56
so that becomes 2 times 25 50 volts okay
00:07:04
numbers now to be simple so that becomes
00:07:07
one that's one will be an only divided
00:07:15
by R well there's actually one two three
00:07:18
four five different hours on here
00:07:21
because we want to find the current
00:07:23
through that one its car to so that
00:07:27
becomes r2 which is 50 55 50
00:07:34
is one amp that's occurring there this
00:07:38
one can be done exactly the same way if
00:07:41
you needed to calculate it because it
00:07:43
would be I 2 is equal to V 1 this time I
00:07:48
divided by R 3 so they wanted curd it's
00:07:51
the same thing becomes 50 again and it's
00:07:54
divided by 50 and that is also why back
00:08:00
then means is 2 amps will come up it
00:08:03
will split evenly 1 amp goes without 1 1
00:08:06
it gets one and there's your answers to
00:08:09
those things there okay let's try it
00:08:14
again with a different set of values
00:08:17
Maurice Nicoll suppose in a sense it's
00:08:20
harder to work out 10 25 33 so as before
00:08:27
we will need to calculate the parallel
00:08:30
part first and remember two plus one
00:08:41
over r3 put calculators ultimately 33 as
00:08:55
well this way we can use that calculator
00:08:58
and remember the bottom we use the exit
00:09:02
- 125 X -1 + 33 X the minus 1 equals
00:09:13
okay set fractions most calculators need
00:09:16
to do that now we must to X the mods 1
00:09:19
your answer excellent 1 again press the
00:09:22
equals come down a fraction yesterday
00:09:25
comes out there 14.2 okay
00:09:47
you
00:09:49
our original one was 10 so we can then
00:09:54
work out Artie Artie becomes R 1 plus R
00:10:02
4 because we're now looking at the
00:10:04
series part and if we put these figures
00:10:07
in 10 plus
00:10:18
don't read the unit so that is now Artie
00:10:33
how can we now do we can now work out
00:10:35
the currents for these ones here
00:10:39
okay so work out the currents then and
00:10:42
work out my t i1 and i2 as before so
00:10:47
let's start with my tea
00:10:49
that's nice simple one because we can
00:10:52
just look at this here Emma IT is here
00:10:59
here because these are the same circuits
00:11:03
I've been working out here therefore
00:11:06
mighty fusing vs divided by RT so total
00:11:14
total and a total 20 2,400 divided by 2
00:11:32
and if we did it into the calculator we
00:11:34
will get 4 point 1 3 amps so that then
00:11:43
is the current flowing through in all
00:11:45
these locations so mighty four point 1 3
00:11:52
amps we can now work out I 2 and I 1
00:12:01
they are done exactly the same way as we
00:12:04
did before so let's do I 1 which will be
00:12:08
Ohm's law they divided by R but it's
00:12:12
which V so it's not vs remember because
00:12:14
it's not a total which one I work out it
00:12:16
has to be the voltage that is in this
00:12:18
section of the circuit so we'll call
00:12:21
that 1 V 1 and we want to find that
00:12:29
current there so he's r2 so we've got to
00:12:34
work out V 1 which the moment we don't
00:12:36
know r2 we do know what that is that is
00:12:40
25 so we've got to find V 1 so let's
00:12:43
find V 1 V 1
00:12:46
is I times R from straightforward law
00:12:50
but is which current or we only know
00:12:52
that current can't use this because we
00:12:54
got current through that we can look at
00:12:56
this circuit because this here is all of
00:13:00
that so that becomes I T times our force
00:13:05
look at the series we made up so that
00:13:09
becomes four point one three times our
00:13:13
four G's fourteen point two two and if
00:13:20
we pull out to a character later via
00:13:31
fifty eight point seven three rounded up
00:13:36
and this will be volts so that then
00:13:41
these are V 1 so that is what goes up
00:13:44
here fifty eight point seven three we
00:13:50
then do 58.7 3/25 yet 2.35 amps in that
00:14:04
part we can now work out what I 2 will
00:14:07
be the last time we did I draw again
00:14:11
however weekend is we can apply
00:14:13
Kirchhoff's current law and that I T
00:14:17
minus I 1 so we know I t's 4.13 we take
00:14:26
away the upper current which is two
00:14:27
point three five
00:14:37
is 1.78 so there's our three currents
00:14:46
flow around in this circuit
