[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:01.09,0:00:05.12,Default,,0000,0000,0000,,Okay now we want to find Thevenin\Nusing the external voltage method, so
Dialogue: 0,0:00:05.12,0:00:10.25,Default,,0000,0000,0000,,our Thevenin is going\Nto be equal to Vex/Iex.
Dialogue: 0,0:00:10.25,0:00:12.34,Default,,0000,0000,0000,,We do is we go back to our circuit, and
Dialogue: 0,0:00:12.34,0:00:16.25,Default,,0000,0000,0000,,we add in an arbitrary\Nvoltage source we can Vex.
Dialogue: 0,0:00:16.25,0:00:19.08,Default,,0000,0000,0000,,Since it's arbitrary,\Nwe can say it's equal to 1 volt, and
Dialogue: 0,0:00:19.08,0:00:23.53,Default,,0000,0000,0000,,that makes our equation very\Nsimple Then we will have an IEX.
Dialogue: 0,0:00:23.53,0:00:25.40,Default,,0000,0000,0000,,We don't know what that is yet.
Dialogue: 0,0:00:25.40,0:00:28.50,Default,,0000,0000,0000,,We solve the problem in much the same\Nway as we did before, so watch for
Dialogue: 0,0:00:28.50,0:00:29.88,Default,,0000,0000,0000,,the differences.
Dialogue: 0,0:00:29.88,0:00:34.60,Default,,0000,0000,0000,,Our first equation is going to\Nbe VC minus 68 volts divide by
Dialogue: 0,0:00:34.60,0:00:40.04,Default,,0000,0000,0000,,6 ohms plus Vc minus 4 IX
Dialogue: 0,0:00:40.04,0:00:44.63,Default,,0000,0000,0000,,divided by 2 omes plus vc minus va,
Dialogue: 0,0:00:44.63,0:00:49.85,Default,,0000,0000,0000,,divided by 6 omes and that's equal to\N0.No change in our first equation.
Dialogue: 0,0:00:49.85,0:00:54.46,Default,,0000,0000,0000,,The second equation is going to\Nbe va A minus by VC divided by
Dialogue: 0,0:00:54.46,0:00:59.74,Default,,0000,0000,0000,,six ohms plus VA minus zero\Ndivided by four ohms plus
Dialogue: 0,0:00:59.74,0:01:04.69,Default,,0000,0000,0000,,alright if I had done BA minus BEX I would\Nof had to divide by zero because there's
Dialogue: 0,0:01:04.69,0:01:09.38,Default,,0000,0000,0000,,zero resistance in this arm instead what\NI'm going to do is I'm going to add in
Dialogue: 0,0:01:09.38,0:01:12.61,Default,,0000,0000,0000,,the outgoing current the current\Ncoming were going to subtract it out.
Dialogue: 0,0:01:12.61,0:01:14.92,Default,,0000,0000,0000,,Iex =0.
Dialogue: 0,0:01:14.92,0:01:19.89,Default,,0000,0000,0000,,Our third equation is going to be the same\Nwe had before in order to find our Ix
Dialogue: 0,0:01:19.89,0:01:25.30,Default,,0000,0000,0000,,unknown, which will be Vc-Va\Ndivided by 6 ohmes=Ix.
Dialogue: 0,0:01:25.30,0:01:30.54,Default,,0000,0000,0000,,Now let's take stock of our knowns and\Nunknowns.
Dialogue: 0,0:01:30.54,0:01:36.05,Default,,0000,0000,0000,,We have an unknown voltage Va and\NVa and unknown current Ix and Iex.
Dialogue: 0,0:01:36.05,0:01:38.10,Default,,0000,0000,0000,,So I need one more equation.
Dialogue: 0,0:01:38.10,0:01:41.86,Default,,0000,0000,0000,,Well since this is a current I'm looking\Nfor let's just put a note right here and
Dialogue: 0,0:01:41.86,0:01:45.26,Default,,0000,0000,0000,,I can add up my ingoing and\Noutgoing currents.
Dialogue: 0,0:01:45.26,0:01:50.19,Default,,0000,0000,0000,,So Ix is comming in, Iex is comming in and
Dialogue: 0,0:01:50.19,0:01:53.26,Default,,0000,0000,0000,,then what's going out is this current\Nright here, let's call it I4.
Dialogue: 0,0:01:54.71,0:01:56.59,Default,,0000,0000,0000,,And that is going to be.
Dialogue: 0,0:01:56.59,0:02:01.46,Default,,0000,0000,0000,,Sorry, that's going to be equal\Nto Va divided by four ohms.
Dialogue: 0,0:02:01.46,0:02:04.52,Default,,0000,0000,0000,,These are the incoming currents,\Nthat's the outgoing current.
Dialogue: 0,0:02:04.52,0:02:06.59,Default,,0000,0000,0000,,Then we put this together\Ninto a matrix equation,
Dialogue: 0,0:02:08.41,0:02:11.15,Default,,0000,0000,0000,,it's going to be a four\Nby four matrix equation.
Dialogue: 0,0:02:11.15,0:02:17.47,Default,,0000,0000,0000,,So equation one, two, three,\Nand four for unknowns Va.
Dialogue: 0,0:02:17.47,0:02:23.23,Default,,0000,0000,0000,,Vc, Ix, and Iex.
Dialogue: 0,0:02:23.23,0:02:27.78,Default,,0000,0000,0000,,My unknowns will be Va, Vc, Ix, and
Dialogue: 0,0:02:27.78,0:02:32.38,Default,,0000,0000,0000,,Iex and And\Nthat will have a set of four constants.
Dialogue: 0,0:02:32.38,0:02:35.34,Default,,0000,0000,0000,,So my first equation,\Nwhat's multiplied by Va?
Dialogue: 0,0:02:35.34,0:02:37.28,Default,,0000,0000,0000,,It's minus one-sixth.
Dialogue: 0,0:02:37.28,0:02:38.98,Default,,0000,0000,0000,,What's multiplied by Vc?
Dialogue: 0,0:02:38.98,0:02:43.10,Default,,0000,0000,0000,,It's one-sixth plus\None-half plus one-sixth.
Dialogue: 0,0:02:43.10,0:02:45.04,Default,,0000,0000,0000,,What's multiplied by Ix?
Dialogue: 0,0:02:45.04,0:02:46.40,Default,,0000,0000,0000,,Minus four halves.
Dialogue: 0,0:02:46.40,0:02:48.30,Default,,0000,0000,0000,,And what's multiplied by Iex0?
Dialogue: 0,0:02:48.30,0:02:49.96,Default,,0000,0000,0000,,What's my constant?
Dialogue: 0,0:02:49.96,0:02:50.92,Default,,0000,0000,0000,,Take that over there.
Dialogue: 0,0:02:50.92,0:02:53.63,Default,,0000,0000,0000,,It'll be 68/ 6.
Dialogue: 0,0:02:53.63,0:02:59.65,Default,,0000,0000,0000,,Ok second equation,\Nlets multiply Va 1/6 Vc
Dialogue: 0,0:02:59.65,0:03:04.69,Default,,0000,0000,0000,,1/6, I left out a 1/4 here.
Dialogue: 0,0:03:04.69,0:03:09.80,Default,,0000,0000,0000,,Then minus one times I ex and\Nnothing times no constants
Dialogue: 0,0:03:09.80,0:03:14.58,Default,,0000,0000,0000,,Third equation minus one sixth,\NVc is one sixth and
Dialogue: 0,0:03:14.58,0:03:19.94,Default,,0000,0000,0000,,Ix is -1, the zero basically brought\Nthe Ix over, zero right there.
Dialogue: 0,0:03:19.94,0:03:24.73,Default,,0000,0000,0000,,Fourth the equation 1 times Ix,\N1 times IEx, let's bring this over here,
Dialogue: 0,0:03:24.73,0:03:30.37,Default,,0000,0000,0000,,it will be minus one fourth and\Nnothing times Vc and again no constant.
Dialogue: 0,0:03:30.37,0:03:35.69,Default,,0000,0000,0000,,When I solve this What I will find\Nis that Iex which will come out my
Dialogue: 0,0:03:35.69,0:03:39.88,Default,,0000,0000,0000,,vector is going to be equal\Nto be equal to 0.196.
Dialogue: 0,0:03:39.88,0:03:47.22,Default,,0000,0000,0000,,Then, when I take our Thevenin which is\Nequal to Vex which was 1 divided by 0.196,
Dialogue: 0,0:03:47.22,0:03:52.39,Default,,0000,0000,0000,,I will find our Thevenin Is equal to,\Nlet me just invert that-
Dialogue: 0,0:03:56.64,0:03:59.45,Default,,0000,0000,0000,,five wholes.
Dialogue: 0,0:03:59.45,0:04:04.40,Default,,0000,0000,0000,,So that's how we find the Rth Thevenin\Nusing the external voltage method.
Dialogue: 0,0:04:04.40,0:04:07.18,Default,,0000,0000,0000,,Again we could measure,\Nwe could simulate or
Dialogue: 0,0:04:07.18,0:04:09.05,Default,,0000,0000,0000,,we could calculate as we did in this case.