WEBVTT

00:00:00.060 --> 00:00:01.859
On the bottom because I can
see that you couldn't see it.

00:00:02.890 --> 00:00:07.480
Okay, when we first started this
problem we were given Vs Is and that

00:00:07.480 --> 00:00:12.950
the resistances and we were asked to find
all of the currents which we just did.

00:00:12.950 --> 00:00:16.950
Now we'd like to be able to find
the power from this particular source.

00:00:16.950 --> 00:00:18.610
Well, how do I find power?

00:00:18.610 --> 00:00:23.130
Let me look in my toolbox of
possible equations to use.

00:00:23.130 --> 00:00:25.190
Here we used Kirchoff's Law.

00:00:25.190 --> 00:00:29.960
And here is how we, and
this is how we calculate power.

00:00:29.960 --> 00:00:34.310
So when I had Kirchhoff's Law I
knew my current source and

00:00:34.310 --> 00:00:38.440
my voltage source and my resistance and
I was able to calculate current.

00:00:38.440 --> 00:00:42.390
Now, if I want power,
I need to have one of these three things.

00:00:42.390 --> 00:00:45.020
I need to have voltage
difference in the current, or

00:00:45.020 --> 00:00:48.520
voltage difference in resistance,
or current in resistance.

00:00:48.520 --> 00:00:52.840
Here I have,
can I have voltage difference and current?

00:00:52.840 --> 00:00:57.130
I certainly have current, I've got I but
I don't have voltage difference.

00:00:57.130 --> 00:00:59.450
So how can I get voltage difference?

00:00:59.450 --> 00:01:02.210
Well, there are several tools that I
have for getting voltage difference.

00:01:02.210 --> 00:01:04.540
And this is actually the one
that I'm going to use.

00:01:04.540 --> 00:01:07.880
If I have, oops, is that the one I want?

00:01:07.880 --> 00:01:11.900
Sure, voltage difference is
current times resistance.

00:01:11.900 --> 00:01:14.180
So I have current, and I have resistance.

00:01:14.180 --> 00:01:17.440
Right here I have current and resistance,
so I can get voltage difference.

00:01:17.440 --> 00:01:20.180
So watch how I'm going
to solve this problem.

00:01:20.180 --> 00:01:25.410
I'm going to use Kirchoff's Law with
my known sources to find current.

00:01:25.410 --> 00:01:32.340
And then I'm going to use my current and
resistance to find voltage difference.

00:01:32.340 --> 00:01:34.817
And then, kind of here in a line,

00:01:34.817 --> 00:01:41.000
I'm going to use my voltage difference and
my resistance to find power.

00:01:41.000 --> 00:01:42.550
So let's see how we do that.

00:01:46.083 --> 00:01:46.855
Let's flip this over.

00:01:48.512 --> 00:01:53.500
Okay, now I know I one,
two, three, and IX.

00:01:53.500 --> 00:01:55.250
I also know my resistances.

00:01:55.250 --> 00:01:56.770
So the next thing I'm going to do.

00:01:56.770 --> 00:01:59.340
Remember I use my
Kirchoff's Law to get those.

00:01:59.340 --> 00:02:02.670
Now I'm going to use Ohm's Law to
find the voltage difference, and

00:02:02.670 --> 00:02:05.790
the voltage difference
is going to be V3 here.

00:02:05.790 --> 00:02:09.720
So V3 is going to be I3 times R3.

00:02:10.810 --> 00:02:15.890
That's the same voltage difference
that is across this current source, so

00:02:15.890 --> 00:02:22.730
if I had V current source, let's call
it VS2, that would be equal to V3.

00:02:24.340 --> 00:02:28.170
Now, I've used my Kirchoff's Law
to find my current.

00:02:28.170 --> 00:02:31.240
I've used my Ohm's Law to
find my voltage difference.

00:02:31.240 --> 00:02:35.510
And now, I want to use my Power
equation in order to find the power.

00:02:35.510 --> 00:02:40.761
So, the power is equal to VS2 times Is,

00:02:40.761 --> 00:02:45.245
which is equal to I3R3 times Is.