WEBVTT
1
00:00:00.340 --> 00:00:02.839 A:middle L:90%
for the first item off. This question we use
2
00:00:02.839 --> 00:00:06.320 A:middle L:90%
for it is law which states that induces electro motive
3
00:00:06.320 --> 00:00:10.199 A:middle L:90%
Force is given by minus that derivative off the flux
4
00:00:10.199 --> 00:00:14.230 A:middle L:90%
of magnetic field with respect to time. The area
5
00:00:14.289 --> 00:00:16.859 A:middle L:90%
that we have to use them for these law is
6
00:00:16.859 --> 00:00:19.750 A:middle L:90%
this area is the area off the circuit, and
7
00:00:19.750 --> 00:00:22.519 A:middle L:90%
that area is changing because this part of the circuit
8
00:00:22.519 --> 00:00:25.609 A:middle L:90%
is moving to the right. Then we can calculate
9
00:00:25.620 --> 00:00:28.660 A:middle L:90%
the flux as follows. The flux off magnetic field
10
00:00:28.940 --> 00:00:32.810 A:middle L:90%
is given by the integral off D A, which
11
00:00:32.810 --> 00:00:36.950 A:middle L:90%
is an area element times the magnetic field. Be
12
00:00:37.820 --> 00:00:43.280 A:middle L:90%
now notice the following the orientation off that surface A
13
00:00:44.170 --> 00:00:46.329 A:middle L:90%
is given by your vector that is normal to the
14
00:00:46.329 --> 00:00:49.479 A:middle L:90%
surface. A factor that is normal to the surface
15
00:00:49.490 --> 00:00:52.899 A:middle L:90%
is a factor that is pointing either our ports or
16
00:00:52.909 --> 00:00:56.100 A:middle L:90%
in words. We can choose the orientation of that
17
00:00:56.109 --> 00:00:59.350 A:middle L:90%
factor. It is conventional to choose, eat as
18
00:00:59.350 --> 00:01:03.200 A:middle L:90%
pointing outwards. So the vector e should be something
19
00:01:03.200 --> 00:01:07.750 A:middle L:90%
like this. Then I'm going with this convention.
20
00:01:08.200 --> 00:01:11.560 A:middle L:90%
The reform. You can see that A and B
21
00:01:11.569 --> 00:01:15.900 A:middle L:90%
are untie parallel so we can write it as minus
22
00:01:15.900 --> 00:01:21.170 A:middle L:90%
the integral off D A times be where now we
23
00:01:21.170 --> 00:01:25.219 A:middle L:90%
are working with magnitudes The magnitude of the magnetic field
24
00:01:25.230 --> 00:01:27.670 A:middle L:90%
is constant So we have miners b times the integral
25
00:01:27.670 --> 00:01:30.500 A:middle L:90%
off the A which is just the area. So
26
00:01:30.500 --> 00:01:34.400 A:middle L:90%
the flux is minus B times a The area off
27
00:01:34.400 --> 00:01:38.140 A:middle L:90%
that rectangle is given by the product off its size
28
00:01:38.150 --> 00:01:41.969 A:middle L:90%
. So the flux is my news. Be times
29
00:01:42.219 --> 00:01:47.260 A:middle L:90%
l which is these side times is more l which
30
00:01:47.829 --> 00:01:52.430 A:middle L:90%
is disorder site Now we can take the derivative respect
31
00:01:52.439 --> 00:01:56.920 A:middle L:90%
Time to get the following Mine has been times l
32
00:01:56.930 --> 00:02:00.489 A:middle L:90%
They are constant times the l divided by the teeth
33
00:02:00.890 --> 00:02:04.799 A:middle L:90%
The LTTE is the reach off change off l which
34
00:02:04.810 --> 00:02:07.129 A:middle L:90%
is the same as the velocity off this bar search
35
00:02:07.139 --> 00:02:12.500 A:middle L:90%
results in minus b times l a times we there
36
00:02:12.500 --> 00:02:16.590 A:middle L:90%
afford induce it e n f is minus minus beat
37
00:02:16.770 --> 00:02:21.150 A:middle L:90%
LV which results in B times L A times.
38
00:02:21.150 --> 00:02:29.699 A:middle L:90%
We therefore plugging the numbers we get 0.75 times 0.65
39
00:02:29.710 --> 00:02:31.689 A:middle L:90%
times five, which results in an e m F
40
00:02:32.240 --> 00:02:39.409 A:middle L:90%
off 2.4375 which can be rounded to 2.4 votes.
41
00:02:39.460 --> 00:02:43.090 A:middle L:90%
And this is the answer to the first item before
42
00:02:43.090 --> 00:02:46.259 A:middle L:90%
proceeding. Let me clear my board. Okay.
43
00:02:46.270 --> 00:02:49.310 A:middle L:90%
The second item has three super items in all of
44
00:02:49.319 --> 00:02:50.689 A:middle L:90%
them. We have to do to remind what is
45
00:02:50.689 --> 00:02:53.650 A:middle L:90%
the direction of the current, but using different methods
46
00:02:53.240 --> 00:02:57.550 A:middle L:90%
, The first item would have to use the magnetic
47
00:02:57.550 --> 00:03:00.699 A:middle L:90%
force that is acting on the current. So you
48
00:03:00.699 --> 00:03:04.349 A:middle L:90%
let us suppose that there is a charge seating right
49
00:03:04.349 --> 00:03:07.840 A:middle L:90%
here? Discharge is a charge Q. Then the
50
00:03:07.840 --> 00:03:13.620 A:middle L:90%
magnetic force acting on these charge is given by cube
51
00:03:13.860 --> 00:03:17.780 A:middle L:90%
times V cross beat. We can see that in
52
00:03:17.780 --> 00:03:23.110 A:middle L:90%
the situation V is pointing to the right while B
53
00:03:23.389 --> 00:03:29.120 A:middle L:90%
is pointing inside the board like this. Then using
54
00:03:29.120 --> 00:03:31.750 A:middle L:90%
the right head who we conclude that the magnetic force
55
00:03:32.300 --> 00:03:38.389 A:middle L:90%
we will be pushing the charge upwards. So the
56
00:03:38.400 --> 00:03:43.069 A:middle L:90%
magnetic force pushes the charge in this direction, which
57
00:03:43.069 --> 00:03:47.080 A:middle L:90%
means that they induce a current is a counterclockwise current
58
00:03:47.250 --> 00:03:52.780 A:middle L:90%
like this. Now, in the second soup item
59
00:03:52.780 --> 00:03:55.150 A:middle L:90%
, we have to use foreign Desslok Well, you
60
00:03:55.150 --> 00:04:00.069 A:middle L:90%
noticed that the flux is negative and it's negative and
61
00:04:00.069 --> 00:04:04.069 A:middle L:90%
decreasing the reform. We have the derivative off the
62
00:04:04.069 --> 00:04:09.439 A:middle L:90%
flux off magnetic field beings. Moledet Zero before to
63
00:04:09.439 --> 00:04:13.039 A:middle L:90%
compensate for that we need an e M F that
64
00:04:13.039 --> 00:04:16.230 A:middle L:90%
is bigger than zero. It means that, according
65
00:04:16.230 --> 00:04:19.930 A:middle L:90%
to the orientation that we had chosen that the electric
66
00:04:19.930 --> 00:04:25.060 A:middle L:90%
current should run counter clockwise. So this is how
67
00:04:25.209 --> 00:04:28.949 A:middle L:90%
you use for a these lot to solve these questions
68
00:04:29.490 --> 00:04:30.689 A:middle L:90%
. Now for the last item, we have to
69
00:04:30.689 --> 00:04:35.029 A:middle L:90%
use lenses Low Liz Low is very similar to far
70
00:04:35.029 --> 00:04:39.019 A:middle L:90%
these law, but instead of treating the E.
71
00:04:39.019 --> 00:04:41.750 A:middle L:90%
M F, it treats the magnetic field directly.
72
00:04:42.410 --> 00:04:44.850 A:middle L:90%
So you you have to think about the same things
73
00:04:45.470 --> 00:04:46.949 A:middle L:90%
. Something has to happen in order for the flex
74
00:04:46.949 --> 00:04:49.550 A:middle L:90%
. Two becomes motor. Two things can happen.
75
00:04:49.879 --> 00:04:53.389 A:middle L:90%
They are quite equivalent. From a general point of
76
00:04:53.399 --> 00:04:56.560 A:middle L:90%
view, these two things are there. Should there
77
00:04:56.560 --> 00:05:00.319 A:middle L:90%
must be a positive IMF more. On the other
78
00:05:00.319 --> 00:05:03.360 A:middle L:90%
hand, some magnetic field should be induced in the
79
00:05:03.360 --> 00:05:06.870 A:middle L:90%
opposite direction off the doctor on magnetic field in order
80
00:05:06.870 --> 00:05:11.959 A:middle L:90%
to lower the floods off magnetic field lines. In
81
00:05:11.959 --> 00:05:15.310 A:middle L:90%
order for this to happen, these inducing magnetic few
82
00:05:15.310 --> 00:05:17.259 A:middle L:90%
to shoot points to an opposite direction with respect to
83
00:05:17.259 --> 00:05:20.779 A:middle L:90%
the background magnetic field. So we have a background
84
00:05:20.779 --> 00:05:26.230 A:middle L:90%
magnetic field pointing in wards, the reform, these
85
00:05:26.240 --> 00:05:30.379 A:middle L:90%
reducing magnetic future point outwards and the magnetic field pointing
86
00:05:30.389 --> 00:05:34.500 A:middle L:90%
our parts is induce it by a current that goes
87
00:05:34.509 --> 00:05:40.930 A:middle L:90%
in this direction in that circuit so that outwards pointing
88
00:05:40.930 --> 00:05:45.350 A:middle L:90%
magnetic field is endings that by a counterclockwise current,
89
00:05:45.790 --> 00:05:47.350 A:middle L:90%
and this is how you can use lenses low to
90
00:05:47.350 --> 00:05:51.389 A:middle L:90%
justify the answer for the second item. Finally,
91
00:05:51.470 --> 00:05:54.860 A:middle L:90%
we have to calculate the current from the resistor.
92
00:05:54.870 --> 00:05:57.689 A:middle L:90%
For that we can use orders. Law homes Low
93
00:05:57.689 --> 00:06:00.769 A:middle L:90%
tells us that the voltage difference is equals to the
94
00:06:00.769 --> 00:06:04.110 A:middle L:90%
resistance off that resistor times the current. So the
95
00:06:04.110 --> 00:06:08.970 A:middle L:90%
current is the voltage divided by the resistance on these
96
00:06:08.970 --> 00:06:15.439 A:middle L:90%
results. In chu 0.4375 divided by 25 noticed that
97
00:06:15.449 --> 00:06:17.180 A:middle L:90%
I'm using the voters. We wrote approximations to get
98
00:06:17.180 --> 00:06:20.540 A:middle L:90%
a more accurate results and then the results in a
99
00:06:20.540 --> 00:06:28.220 A:middle L:90%
current that is zero 0.975 and this could be rounded
100
00:06:28.230 --> 00:06:34.660 A:middle L:90%
to 0.0 98 which is 98. Milli amperes uses
101
00:06:34.660 --> 00:06:36.069 A:middle L:90%
the answer to the last item