Oh, hello.
Welcome to Michael's Toys the first and only show on YouTube made by, of, and for teenagers who like to cook
I'm your host Michael Stevens and today
We are going to be talking about magnets, specifically the strongest magnetic field my body has ever been inside
The 3 tesla MRI at UC Irvine
Which I guess kind of makes this an episode of UC Irvine's toys because they own the MRI, I don't.
Anywho, I had a lot of MRI scans done of
My brain for MindField season two and I learned a lot about them, and they are... just beautiful and wonderful.
Here's a question how strong are different magnets?
Well, one way of measuring a magnet's magnetic field strength, really its magnetic flux density, is the tesla.
Alright now to put a tesla into perspective, our planet is a big magnet, really.
It's not a really strong magnet though– its magnetic field strength is just about maybe 31 microteslas.
In comparison and everyday ordinary refrigerator magnet has a magnetic flux density of about maybe like five milliteslas.
A typical sunspot can have a magnetic flux density of around a third of a tesla, but the surface of a neodymium
rare-earth magnet can have a magnetic flux density around 1.25 tesla.
The MRI machine I got in many many times for MindField season 2 was a 3 tesla machine
Which means you can do some pretty weird things with it. You have to be very very careful:
No ferromagnetic metals are allowed into the room it is in, or even near it in the room outside because it attracts
ferromagnetic materials so quickly that they could be pulled from your hand race through the air at an ever-accelerating rate
until they strike the machine at, like, super-lethal and at least very dangerous speeds.
There are videos on YouTube where people show off just how dangerous the
magnetic power of an MRI can be: it can lift chairs off the ground, but what about metals that aren't attracted to magnets?
Well, they exhibit some v ery strange behaviors and Craig Stark at UC Irvine
was kind enough to allow me to bring in a giant block of aluminum
(chuckles wickedly)
Now I'm gonna have to just talk over this clip because we obviously couldn't bring cameras or microphones
into the room to pick up our voices we had to set the camera far away and then zoom into myself pause
Let's just take a brief moment to appreciate the tan line on my face caused by my glasses
But here's an aluminum block and I'm gonna set it up on its side, and then let it fall okay, pretty easy
That's a great demonstration of gravity
But watch what happens when I set the aluminum block near the inside of the MRI and let it go
Anti-gravity
But not really. It's actually a demonstration of Lenz's law
Veritasium has a fantastic video on the topic and I see it coming up on Reddit
Quite frequently so I had to do it myself, it's really fun these are very powerful magnets
And I'm gonna drop them so that they fall
Only due to gravity. Here we go: three, two, one
there it is 9.8 m/s^2, for those of you counting at home, but now I'm gonna drop them through a copper pipe.
Copper has no interest in magnets, or maybe magnets don't care about them
Or do they? Well we're gonna find out. Notice that if I try to stick the magnets magnets to the copper, it not
Doesn't work, but if I drop them through
watch what happens. Three two one
They fall really slowly. Here we go one more time three two one
Something's slowing them down. You can hear that they are hitting the sides of the copper
But they don't have to do that if my magnet was a better shape it wouldn't happen, and they would just glide right on down
They really are more slowly. Let's look at it from above.
Here are the magnets being dropped by themselves.
That's how long it takes for them to fall to the table
three two one
That's it
But now let's drop them through this copper pipe. Okay ready three two one
Look at that! Let's try it one more time.
Three, two one, and they hit. Much much slower.
To see what's going on, let's play around with magnets. One of my favorite magnetic fun recipes is a one that I learned from Science Bob
Fantastic guy.
It involves breakfast cereals and a bowl of water.
So here's my bowl of water now what I need to do is grab myself one little flake of this corn flake-like cereal
Now many breakfast cereals are fortified with iron
And it's not iron in any kind of compound. It's literally just elemental iron.
If I float a little piece of cereal there in the water looks pretty boring
But now let's bring a magnet near it.
Ohhhh! Look at that! It follows the magnet! I'll come in from the other side so you can see that
it wasn't just some sort of property of the water
C'mon, little cereal flakey. Yeah.
Look at that! I'm able to move the cereal across the water by attracting the iron inside it with a magnet.
When you eat many foods you're eating just straight-up elemental iron like the kind
We make nails out of just like a lot less than would be in a nail. Oh I love that
I hope it's clear for you guys to see this demo wasn't really related to MRIs
I just thought it would be really fun to do to really start talking about why that block of aluminium fell
So slowly around that strong magnetic field we need a more advanced recipe
but I think you guys are ready for it what we're gonna need for this recipe is a
really
nice
big
nail
You're also going to need... let's see this one looks good
Oh, perfect, yeah.
You're gonna need some copper wire that's thinly insulated.
You might need more than this, but what you're gonna want to do is take your wire and coil it around your nail.
Make the coil nice and tight
Keep them all bunched together, so you get as many wrap arounds of the wire around the nail as you can get and then
When you're done
You'll want to connect the two ends of the wire to a battery now
That might take a while so because of the magic of a TV cooking show I prepared an electromagnet earlier
Oh yeah it's ready, this is good this is really good.
Okay...now...
Perfect. Ohh yeah.
Hey...!
Just like mom used to make. Um, we've got here a big battery,
and we've got a nail that is just coiled with lots and lots of wire. I think that
We let the paperclip simmer long enough. I'm gonna go ahead and put them
There on our aluminum foil and I'll demonstrate that at this moment
Because the wires are not completing a circuit the nail
Is not magnetic, has no effect on the paper clips
But now let's connect this wire to the negative terminal and see what happens
Ooh, OK, we're live, and...
Yeah!
Now let's turn off the current.
Oh! Hoohoohoo!
All right, so what we've learned is that current flowing creates a magnetic field.
What's even more fascinating is that a moving magnetic field can
also generate electric current there are fantastic videos online showing you how to do this.
By simply spinning a magnet around a coil of wire. You can light a light up
This is how electric generators work. All you need is something to keep the magnet spinning, like wind or falling water, and
Your coil will supply electric current
There's a very interesting loop going on here: electric current produces a magnetic field
but a moving magnetic field can produce electric current
Now, this is key to why the block of aluminum falls so slowly near a strong magnet.
It's also why even things like living frogs can be levitated if your magnet is strong enough
Not all materials are attracted to magnets this nail is made of iron and
Well the magnet loves it a whole lot but this copper tube...
Nothing. The magnet just doesn't care at all.
But what copper *can* do is conduct electricity
and since a moving magnetic field can induce electric current in a conductor
If we put these together and move one of them well then we should be able to produce some current
But we also know that electric current creates a magnetic field
Which means we could make the copper act like a magnet by inducing current in it.
Let's try that using this conveniently positioned ribbon I'm gonna take these
Neodymium disk magnets and very carefully slide them apart
It's very important to be safe with magnets
They are attracted to each other so much more strongly the closer they get
that they can easily pinch you, so please be careful with strong magnets.
Okay, here we go... Perfect.
If I bring this nail near the hanging magnets, ooh they love it. They love it.
But the copper they don't really care much for.
Not much interest. Hello? Wake up! No, they don't care.
Watch what happens if I move this copper pipe quickly near the magnets,
oooh
Look at that! Now they're not touching at all, but I'm able to get the magnets moving because
As I move the pipe across the magnets- look at that! well
This is really fun- as I move the pipe
across the magnets the magnetic flux density at each point along this piece of copper changes that creates
an electric current and that electric current, by Lenz's law, will produce a magnetic field
That is opposed to the magnetic field of these magnets causing the hanging magnets to move.
Now the faster you move the materials, the more dramatic the effects.
Oh, yeah!
Beautiful!
This is why the magnets fall through this copper tube so
slowly
By Lenz's law the magnetic field they induce in the copper pipe is
counter to their own magnetic fields you can think about this phenomenon in terms of conservation of energy
Where does the energy come from that produces the electric current in the pipe and the magnetic field? Well it comes from the falling magnets.
They fall more slowly because some of that energy is being converted into electric current.
The currents created by a moving magnetic field are called eddy currents, and if you want to become more eddy-cated about them,
there are links down below where you can learn more.
Now let me address a quick question
You might be having why is a video like this on the DONG channel and not on Vsauce1?
Well I answered this question on Reddit yesterday and
The long and the short of it is that in my opinion both channels have sort of different goals. My goal on Vsauce1 is
to upload videos where I get to share the things and the new framings that caused a concept to finally click in my head
Concepts that I never thought I'd be able to wrap my head around before
Now doing that can take a long time
I've been working for a while on an episode about rotational phenomenon specifically some counterintuitive ones
And I'm not happy on Vsauce 1 just using vocab words like torque and moment of inertia to describe what's going on
I want to define what those words mean and ask why
over and over again so far back that we're left with nothing but
Geometric principles and symmetries of the universe that can take a while, so thank you for your patience
I hope that you you share my passion for the topic when the episode comes out and think that it's worth it
But on the DONG
channel, I'm able to share things really quickly without disappointing people who expect something deeper in fact in this year
So far in just 2018. I've already made now 10 episodes on DONG
That's more than I made on Vsauce 1 all of last year so I love DONG
But I remain steadfastly committed to
Both
Channels
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And, as always, thanks for watching.
That MRI at UC Irvine by the way is a giant electromagnet, but it doesn't take a huge amount of power to run because
It's really cool
Cold, like, really cold.
It's cooled by liquid helium near absolute zero so it becomes a superconductor
And there's almost no resistance
You literally throw some charge in there, some current starts going through, and it gets so cold that it becomes a persistent charge.
And it just remains an electromagnet unlike my nail which is not a superconductor and well when the currents turned off it
stops being a magnet
In fact, if you want to turn off the magnet in their MRI, you have to quench the MRI
There's this big emergency button you can push if some emergency happens
And the liquid helium is shot out of a big vent, probably on the roof of the hospital building; it's this big plume of
Helium gas and condensed liquid water from the air because it's just so cold and it's well
It's very dramatic
There're videos on YouTube where you can see MRIs being quenched
That will cause resistance to come back into the coil and it will cease to be an electromagnet.
But I love the fact that they just kinda plug it in once,
Power up that electromagnet, end then after that is the energy to keep the helium cool.