This is a prologue to the electromagnetic
induction lab. I just want to point out
when I first, the first version of this
lab, it worked out beautifully when I did
in my office. And then when we actually
did the lab, I thought that would follow.
The students and I recognized what my mistake
was later, sort of. The ten thousand
percent error was not uncommon, and so
this really struggled with why it was so
far off, and I'd spent hours trying to
resolve it. What happened in my office
would have worked out so nicely, was I
think I did circular logic, where I used
an experimental value to ultimately come
up with a theoretical value, which
matched the experimental value. So it was
a boneheaded mistake, and so after I
think two years of people doing the ten
thousand percent error, I revamped it, and
so when I did this one I got really
excited because I was under 100 percent
error. So from, relative to the first
version of this lab it works out
beautifully.
Relative to, let's say the AC circuit lab,
it does not work out as well. So I would
expect it to be under 100 percent error.
I, you know, I'll have the same numbers
you have from in order to do this lab,
so we'll just find out what happens. So,
but, I just want you to know that you
know it gets good results only when you
compare it to the really horrible
results from the previous version. This
lab is the electromagnetic induction lab.
It says 152 there, but probably can be
used for 252 as well. We will see when we
get there. So anyway, so step one we're
talking about two solenoids, and the
solenoids we're talking about are right
here. And so we have the, what is going to
be referred to as the large solenoid, and
what's going to be referred to as the
thin solenoid. So just be aware of that.
This video is also going to be sort of
cut and paste, and so we're just going to
see how well it does. So sorry about, for
the jump cuts, but it's sort of the
nature of the beast. What I'm going to do
for measuring the number of coils, or
distance for the number of coils, so I'm
just going to take a series of photos which
will be sort of spliced after this part
of the video.
For the thin and then for the large, so
there's not going to be any commentary.
Notice that the metric is on the bottom
side here. So see how close I can get and
still be in focus, and that's looking
pretty decent right there. So what I'm
going to do is just take a series of
pictures, and do the measurements from
there. So over the series is the next
couple of pictures that up, and one of
the upper or lower part of the picture
it says option, like thin option one and
option two, large option one large option two;
pick one of the options for counting
the number of wires and using the
measurement there, so that's what it is.
That's what the choices are coming up.
 
All right, so we measured the, the various
thicknesses there, and the, the number of
wires across would be... So what we're
looking at right there the number of
wires across. That is the number of coils
that you would have counted between the
the two ends, or the the two inner pieces,
of the Vernier caliper. The width would
be what's measured on the caliper, so
width right there.
Length of coils, this is going to be a
measurement that I'm going to do now. I'm
going to interject that into the video, and
then outer hole diameter, inner hole
diameter. And then I'll tune back in for
the resistance. So the next several
measurements will be for the length of
coils, L sub sol, d sub hole, and d sub
coil for thin and large. We're going to
interject a little bit here. It's going
to look like that I didn't measure it
properly, but there is an issue of
parallax when I'm dealing with a camera
here, and so I have very carefully lined
up the the inner pieces right here, inner
pieces to match up with the end of the
coil here and the end of the coil here. So
I'm just going to zoom in on the
measurement of it.
And now I'm going to do the
for the large coil, and this one should
actually be a little bit easier. Let's
see if I can get an actually decent
picture going.
 
As you'll notice what I'm doing is I
took a picture of basically of what I'm
measuring, followed by a zoom in of the
actual measurement. And so that's the
pattern I'm going to maintain for at
least a short while.
 
On that last shot, what I was doing is I
was measuring the... what I want is the, I
said outer diameter of hole. Recognize
there's a ring there. What I really care
about is the inner diameter of the coils.
And as a quick and dirty, I put down
outer diameter of hole. So I'm not
actually measuring from inside to inside
here, but outside to outside here. And so
that's what I was actually measuring. And
so there requires a, you know, very
careful measurements there. And probably
doesn't make a huge difference in the
long run considering the percent error
for this lab, but that just so you know
that that's why I was did the
measurement I last did, and I am going to do
the same for the other one. For the four
large.
 
Now I'm measuring the resistance, and so
I have it hooked up to the multimeter.
And it's not a lot of resistance here.
And so it is fluctuating, at least
between 0.0 and 0.1 there
for a moment now.
So the actual resistance is going to be
somewhere in between those two. It's sort
of settled between it. So you can sort of
do an estimate by concentrating on how
much time it spends on zero versus how
much time it spends on one. The more time
it spends on zero, the closer it is to
zero. So don't put down zero there, but
put down an estimate based upon that. I'm
going to try different wires just to see if
I get a different measurement, and we're
going to see how that goes.
Here's with a different set of wires,
here's with a different set of wires for
resistance, and we are getting now a
resistance. It was at 0.2. I think
the camera caught it, and so we're
concentrating more on 0.1.
Now is that a matter of the wires? It
quite possibly is. It would make sense
that the wires is the only difference
between the two. Does one of wires have
more resistance than the other? Again it
looks like it's fluctuating between
0.0 and 0.1, and do an
estimate based on how much time it
spends on each. Again, the more time it spends on one..
oopsy, up to 0.2, and haven't, don't. So
I'm going to make sure the wires are in
tightly. Push in. Push in.
All right, so based upon the the evidence
there decide what you are going to use.
Now for the big one. So finding the
resistance across the large, and this is
many fluctuations have much less
significant impact. You can see it is
still it was fluctuating right there. It
does seem to be fluctuating; however, it's -
this one is not a huge impact if you're
a little bit off. The other one,
unfortunately, yeah,
there is. Now we are going to try a
different way of actually finding the
resistance, but that way it doesn't seem
to be as effective. And I haven't a hundred
percent sure why, but there is an
alternative method for finding it. All
right, and so while we're here I just
want to point out that this bottom
section down here, notice that there's
the asterisk down here. It means that can be done after you've actually collected all
the data, but since you're doing this at
home you can do it slightly differently.
This is just a metric, a unit conversion of,
the measurements that you have up
here, so just be aware that's all that
that is. Also resistivity of copper.
There's so, and don't forget to cite the
source. Some people are still forgetting
to cite sources when I asked them to. All
right, so I'm going to set up for the
next part. The way we have to set up for the DC, the current's coming out of the red
side, that's the high side. It's going to
go through into here, this is my
multimeter measured on currents, in
microamps at the moment, and then
through here into thin, and then from
thin back into the power supply here.
This is measuring the voltage of the
power supply, and this is measuring the
current coming out of the power supply.
It's obviously not a lot of current
right there. The actual value is not as
important as the slope that you're going
to get from the graph, and so I'm not
worrying about the zeroing or trying to
figure out what the base is.
It is turned on, but it is, the voltage
here is right now 124 millivolts,
negative 124 millivolts.
That's just because it's not zeroed
properly. So I'm just going to add just
touch of voltage right there. So now give
it a chance to settle some.
All right, it seems to be slowing down.
We're going to come back to that, just in
case. And the current. Notice the units. It
is microamps.
And at some point, looks like it backed
down, so it's now in sort of the range
where it's going to be, and the voltage
is in the range. And notice that it is
millivolts and that is microamps. So now
let's adjust it again, so we're now going
to adjust it just a little bit. We now
have a different voltage there, and we
have a different current. Notice that on
the table I have that in milliamps, so you
will need to move the decimal point to go
from micro to milli. You'll need to move
it over three places so that would be 0.497,
at least the way it's just, or six,
whatever you decide for the current. And
then our voltage, still roughly what it
was, I think, when we left. All right, so
now I'm going to adjust the voltage just a
little bit more. Ultimately I need five
different voltages, so this is the third
one.
And as that settling down, let's come
over here,
again it's still displaying microamps, and
that's because I actually have the
setting on microamps right there. That
seems to come close to settling. Back
over here for voltage, and I think that's
probably close enough to settling right
there. And then back over here. All right,
so let's adjust one more time, or another
time.
All right, that seems that you to be slowing
down over here. Here's the current. Notice
the current is increasing as we increase
the voltage. And that's what it should be
expected. Also going to do a quick touch
of the thin here, and make sure it's not
too warm, and it's not. All right, it seems
to be oscillating back and forth there.
And that seems to have settled down. Yeah. All right, so what I'm going to do is we're
going to adjust it. This would be the fifth
time. I know I do a sixth one, just so
that you have some options.
All right, that seems to have slowed down. And
then back over here, that is our current,
and that seems to have stabilized there. And
back over here, and it's now oscillating
back and forth, and let's see if we can
get a fifth one in here. At 1.6.
All right, we have not blown the, the
circuit on the power supply, so I think
we're good here. The instructions say 1.5
Volts only. Good, I think it says around
1.5 Volts. Yeah, so that's, this is good
enough. Okay, it's slowing down, and going to
look at the current, and we have current,
and that's looking rather stable there.
And I'm going to zip back over to the
voltage. All right, and I'm now going to
stop this. Set it for the next part. All right,
so we now have the power supply hooked
to the large right here, and I cranked the
voltage adjusts all the way up, and that
is the voltage when it's at 100%. So you
should be able, to I'm hoping that you
can see that. That is the voltage, and
again it's oscillating back and forth,
because that's what we do in physics. So
I'm going to stop it here and set up for
the next step. But we now have sort of
panning back, looking at the whole thing
here, we have current's now going to be
running from the high side here, it's
going to go through the current probe
that's hooked to the LabQuest, and then
through large, and then back into here. So
that's the setup right there. Because we
want a very, very quick glimpse. We, you
know, 10 samples a second is just way too
long in between samples, and so we need
to up that to 10,000m and so that's going
to produce, if you look right there, one
hundred, one hundred eighty thousand and
one samples, and so we need to really cut
that back to five seconds. Really don't
need more than five seconds, but just
want to point out that's where we're
setting this. And then click
okay. The five seconds is just gives a
little leeway. Hopefully it'll just start, stop.
We only need a second, but just in case,
we put in five seconds there. All right, so
we now need to know which way is North,
because we might have to switch
something around here, and so what we're
going to use is the magnetic probe
right there, which will hook through the
LabQuest, and so I'm going to stop this,
and hook that up. Magnetic field sensor hooked
into it. Now the Earth does have its
magnetic field, and there's also a matter
of zeroing. But the Earth does have its
magnetic field, and so that's why you
should be expecting to see something
there, and a picture my thumb very
briefly. And notice at the end of this,
there's that silver dot. Basically I want
the magnetic, it's going to measure the
magnetic field that's running
perpendicular to that hole right there.
And so since I want to know the magnetic
field coming out of the large solenoid
here, I'm going to point it towards that.
Now, what's going to happen is if this is
the North end right here, the North, the
magnetic field is going to be flowing out this way, and assuming going towards, basically,
it's going to be going into this if I'm
pointing towards the North end. If the
magnetic field is going into the sensor,
in that direction, it's going to show up
as negative. And so that's how we know
that the magnetic field is North on this
end, by whether we get a negative reading
over there. So I am going to turn this on
hold this up next to it and notice we
are getting a positive value there, and
does increase as we get closer, and it
decreases it we get farther away. So I
need to flip something around, and
probably the simplest thing to flip
around will be the leads onto this, and
so I'm going to stop this, flip the leads,
make sure I've got to set up right, and
then we will come back. All right so I flipped
the two leads there. The current still
should be going through in the same
direction through the probe, but it now
should be going the opposite direction
in through the sensor here. And so as I
hold this up, notice we now have a
negative value, so that means the North
end is on the right. Again, it
doesn't really matter which side the
North end is, other than just
standardization. It helps me realize the
some values later on. And so that's set
up. I'm going to stop this and set up for
the next part.
So we are about to do this next part, and
what I do want to comment on, being able
to sort of guess which way the magnetic
field is going to be. In the old coils,
that we, the ones that we we still have
some of them, but in the older ones it
was much easier to see. We didn't have
the black tape around here, and it was
very obvious which way the wire was
coming from here, going either... going that
way or that way, and so we could have
actually made a prediction with the
right hand rule. So if the current was
flowing that way, was flowing around like
that, we would wrap her fingers around,
and the North Pole would be out that
side. If the current was flowing around
like this, we could do wrap it around
like that, and the magnetic field is
pointing that way. So, but it's not easy
to tell with these, and so that's one of
the reasons there's, it's part of the
procedure to sort of take a shot at it,
but we don't know for sure. So now we're
going to find minimum and maximum
current. Because we're doing minimum and
maximum, we don't have to zero it, but
zeroing it always just feels good.
And so we have zeroed it. And now I'm
going to run it, and oh, start with that
off.
And now let's zero it, and so now I'm
going to start this, turn that on, turn
that off.
The fact that was not holding steady is
not crucial right there. Also that's not
10,000 samples a second. So let's back up
here. That's still 20 samples a second. Oh,
when I plugged in the new sensor. So
10,000. Done. Change that to five seconds.
Done. Okay. All right, so now let's try
that again. So I'm going to start that.
Turn that on. Turn that off.
Stop. And that's the flower pattern that
shows up when the LabQuest is taking,
it's basically pulling in more data than
it can present, and so it just needs time
to catch up. You'll also see that in the
AC circuit lab as well. And I'm going go
ahead and stop this, and bring it back after
it's finished for this pattern. I just
want to comment a little bit on the
sensor, and while I'm thinking about it.
The, to find the maximum-minimum curve, we
could have used the 10 samples a second,
and really wouldn't have taken that long.
And it would have been nice and easy
But what we really care about is the
rate at which the current is changing,
because the rate at which the current
changes affects the rate at which the
magnetic field is created inside the
solenoid. The rate at which the magnetic
field changes affects the rate at which
the magnetic flux changes. And the rate
at which the magnetic
flux changes affects the induced current
in the thin which we'll measure later. So
that's one of the reasons why we need
10,000 samples a second is because I
really want to know that steep, I want to
figure out how steep that rise is
initially. and it's still going on. I had
to redo it, because there was a glitch in
there. So I'm going to
keep, I'll keep doing it until I get the
non-glitch, but you know, again it's physics.
So not only do we rejoice, but we do
expect things not to work as perfectly
as we hope. So until this thing comes
back with results that look nice. All
right, that is some nice-looking data
right there. All right so what I'm going to
do is first off, let's only look at graph
one, and that steepness right there,
there's a slight slope there, then we
need to narrow that down, so let's zoom
in on that. And let's zoom in again. Oh
man, this is just really nice data. That
is so much better than what I usually
get. All right, so we want to know where
the steepest change is, so I'm going to
highlight the steepest change. It looks
like that is the steepest right there.
That looks slightly steeper than it does
down here. So I'm going highlight that.
Maybe slightly less than that. There that was
a little it better. And curve fit, current,
do have some glare, there seeing if I can do this
without glare. Notice that we do have the
brackets there and there, so that we know
what it's going to be fit, and I want to
do a linear fit. And there we go.
So that is the data that we, you need to
use for number 19, and again don't forget
the units here. That is current in the
vertical axis in amperes, and time in
the horizontal axis in seconds, and the
RMSE, that's the root mean square
error, the correlation there the 0.9993.
That is R in when we do graphs using
Excel or OpenOffice spreadsheet or
Google Docs the correlation. We can
post R-squared, which is just this value
squared, and so to give you some idea of
how the goodness of fit. All right, I'm
going to stop it here, and set up for the
magnetic field bit. After going through
all that I forgot to actually record the
minimum maximum current, and you could
pull it off of the table, so it looks
like a zero and in about 0.15, and that's
all well and good, but I went back the
next day and I recreated that aspect.
I made sure that the
voltage was still the same, and recreated
it, so the next slide, or next couple
slides are basically what I went back
and recaptured in order to get the
maximum of minimum current, so look
forward to it.
 
All right, so this is a basic setup right
here. You're not going to see it when I
actually do it, because I am missing some
extra hands here. So we have the magnetic
sensor right there. I did zero it just to
try to eliminate the effects from the
Earth's magnetic field, and I'll zero it
again just before I start. I'm going to
start with the, this, 10 centimeters out
with the magnetic field 10 centimeters
out then 9, then 8, 7, and then
I'm going to go in and then I'm going to go in
by half centimeters as we go in. Now
there is a maximum amount. This thing is
set on 6.4 milliTesla, so that
should be the maximum. We will get
readings above that, but it becomes
questionable anything above 6.4,
but I'll read it until, you know, either
it just pegs out, doesn't change anymore,
or it just seems, you know, or it we get
to the halfway point. So I'm basing the
the distances based upon this table
right here this is Table four,
and so I'm going to start at 10 centimeters
out, and that's the ten centimeters out
right there. And then go until I am five
centimeters in at most. I'm not
necessarily going to fill in all of it,
and then the theoretical over here, there
is a formula that's given. So, that, you
know, that believe it's written in there
which equation to use. So yep. Equation
six. All right, so what I'm going to do is
I'm going to put it at the, I'm going to tell
you the measurement, or let's see if I
can set this up properly. I'm going to stop
this, and try to set this up properly, and
then we'll run this part of the lab.
All right, so not the best setup, but here
we go. All right, so I have to turn this
thing on.
So 10 centimeters out. 9 centimeters out.
8 centimeters out. 7 centimeters.
6 centimeters. 5 centimeters. 4 centimeters.
3 centimeters.
2 centimeters. 1 centimeter. 0 centimeters.
So we're, this right at the entrance.
And so, oops, it's something like let loose
there. So now we're about to go in half.
Okay, we're... ran. All right, so half centimeter
in 1 centimeter in. One and a half
centimeters in. Two centimeters in. Two
and a half centimeters in. Three
centimeters in. Three and a half. Four.
Four and a half centimeters.
Five centimeters.
For the the next part, we're going to
basically run this trial five different
times, and the main reason we're going to do
it five different times is that even
though we're doing 10,000 samples a
second, we have changes here that are
taking place really fast, on the order of
microseconds, and so we're trying to
capture it. And so, we're going basically
do this five times, hoping that we get
close to actual good goal here. I'm going to
start and stop a couple of times, just
because once I start it, it just takes a
while for it to catch up, and then we'll
do the analysis, and then we'll run the
next one. So, and also the setup over here.
So you come back here, so you can sort of
see the whole mess. We do have the power
supply is hooked up to the large right
here, and then the current probe is
hooked up to the thin. So it's been
talked about before. What's going to
happen is we're going to turn the power
supply on, that's going to in pull, make a
current come through here. As the current
comes through here, it's going to induce a
magnetic field. Inducing the magnetic,
creating the magnetic field that's
created, it creates a magnetic flux, and
the magnetic flux is going to induce a
current in this. Once this reaches a
steady current, there's no change in
the magnetic field, therefore no change
in magnetic flux, and therefore the
current should be zero. So what should
happen is when you turn that on, it's
when the current ramps up, that was the
whole point of that last exercise, when
the current ramps up we will induce a
current in this, and then the current is
steady, no induced current and then we
will, and then should go back down to
zero. When I turn that off, if, it depends
on which I turn off first, but if I
turn the power supply off first, then you
should see a spike showing up again as
the magnetic field starts to collapse,
and then this will induce the current
trying to bolster that up. So, and there
it is. So let's go for trial number one
here. So first we need to turn this on.
Then I'm going turn the power supply on.
Turn the power supply off, and turn that
off, and now we wait. So I'm going to turn
this off till it comes back. All right, so
what we have right there is the spike
that happened when the current was
induced, and I want to get maximum and
minimums value, so I don't need to zoom in,
but I highlight a certain area there, and
I go to statistics, current. So after I
had done that recording, I realized that
there are times when you turn on the
power supply, and you get a big spike, and
then you get the big current, so for some
reason there's a just a glitch in the
power supply. So you get a big spike, goes
back to zero in the current, and then you
get the the current like we saw earlier.
Now when we did the trials earlier, and
we had that huge spike before we had the
normal looking curve, I threw those out.
Now apparently what happened here is
that I had a couple of trials where we
had that huge spike, and the current
sensor pegged out, and so there was a
series of trials which were just bad
data. So I went back the next day, and I
recreated that part of the experiment. So
the next couple of slides are just
pictures of the data that I got from,
from normal operations, and so that's
what you're about to see
 
Oh, I do want to point out over here
where it says calculate the experimental
induced current by subtracting the
smaller from the larger. This is in case
it just didn't get zeroed properly. And so
it's establishing what zero is by doing
that. And enjoy.
I think. The oh, enjoy. What am I talking
about. Don't forget, rejoice, because
this is physics.
