WEBVTT

00:00:01.700 --> 00:00:05.346
Okay, now, there's another little
part V2 and that's right here.

00:00:05.346 --> 00:00:10.988
Notice that I forgot to do V2 and
so we go 6 minus 4 across there,

00:00:10.988 --> 00:00:15.823
and so we can see at that
voltage V2 is equal to 2 volts.

00:00:15.823 --> 00:00:17.390
So let's just write that one down also.

00:00:17.390 --> 00:00:22.337
So V2 = 6- 4 volts, okay great,

00:00:22.337 --> 00:00:25.720
so that's 2 volts.

00:00:25.720 --> 00:00:29.417
Now, we need to use that down
in the next one right here.

00:00:29.417 --> 00:00:31.640
So I've already written V2 as 2 volts.

00:00:31.640 --> 00:00:33.900
So I've written the voltage
differences across here, and

00:00:33.900 --> 00:00:39.940
what we want to find are Va, Vb, and
Vc with this being our ground location.

00:00:39.940 --> 00:00:41.790
Okay, so how do we do that?

00:00:41.790 --> 00:00:46.910
Let's just go from maybe we can even just
do the same tracks that we did before.

00:00:46.910 --> 00:00:52.750
But let's just go from Va down to ground
like this and let's just calculate it.

00:00:52.750 --> 00:00:56.470
So we would say Va and
that would be minus grounds.

00:00:56.470 --> 00:01:01.943
So Va- 0 =, okay plus V2 which

00:01:01.943 --> 00:01:08.588
is 2 volts plus V3 which is- 8 volts,

00:01:08.588 --> 00:01:13.287
so now Va = 6 volts, okay?

00:01:13.287 --> 00:01:19.921
Now, let's see what Vb is,
let's go from Vb down to ground,

00:01:19.921 --> 00:01:24.650
well Vb- 0 = plus V3 which is- 8 volts.

00:01:26.390 --> 00:01:27.500
Now, let's get Vc.

00:01:27.500 --> 00:01:31.640
Okay, to get Vc, let's go,
here's an easy way.

00:01:31.640 --> 00:01:34.590
We can go Va to Vc cuz
we know what Va is now.

00:01:34.590 --> 00:01:37.765
But I'm just gonna go Vc down to ground,
this route right here.

00:01:37.765 --> 00:01:42.925
So Vc minus ground 0 is equal

00:01:42.925 --> 00:01:50.020
to plus 20 volts plus a -32 volts,

00:01:50.020 --> 00:01:55.180
so that's = -12 volts.

00:01:55.180 --> 00:01:58.630
Okay, now what we can observe
about this circuit is,

00:01:58.630 --> 00:02:03.530
if we move the ground around,
the node voltages will in fact change.

00:02:03.530 --> 00:02:07.510
However, the voltage differences
between any two parts of the circuit

00:02:07.510 --> 00:02:11.690
are going to stay exactly the same
even as we move the ground around.

00:02:11.690 --> 00:02:16.340
Okay, now problem 126 has you re-do
this problem with the ground right here.

00:02:16.340 --> 00:02:19.720
So why don't you stop the video, see if
what you could do with a ground right

00:02:19.720 --> 00:02:23.394
there, and check it against
the solution for problem 20