Last month I made a video about an exploding can.
It was an electromagnet that cut a can in half
and it was like boom.
And that was awesome.
But what you guys were really interested in was this.
It's a tiny little quarter.
Look, it's a itty bitty George Washington.
Yeah, I made it into an earring.
We shrunk a quarter, or rather the performance group ArcAttack
shrunk a quarter using an electromagnet.
But you guys were really curious on how that worked.
How do you do this?
So I'm going to get more into that, like an elf gets
into the hobbit hole.
Is there going to be a bang?
I'll tell you, there's going to be a bang.
There's going to be a bang.
It is going to be a bang.
Oh, geez.
OK, it's ready.
Oh, it's ready?
You guys ready for this?
Everybody good?
Whoa, that was a huge explosion.
Oh, my gosh.
Oh, there he is.
Ouch, ouch.
Is it a little hot?
Look at that thing.
That is how you shrink a head.
Wouldn't it b e cool if you could see the coin shrinking?
Oh wait, the group Hackerbot Labs is setting up
a quarter between two clear dowels in this video
with a Phantom high speed camera to capture the process
at 180,000 frames per second.
And that's it.
Here's a euro being shrunken.
It's that fast.
Only seven frames at 180,000 frames per second.
Then the coil explodes.
Another cool thing, you can actually
do this with all different kinds of coins.
It doesn't have to be a quarter.
So I came across this website called CapturedLightening.com,
Bert's Quarter Shrinking and Can Crushing Gallery.
He's got all kinds of different coins, even the ones
with the circle in the middle so you
can see what happens when you shrink
all different kinds of currency from different countries.
And with this one, you can really
see that you're shrinking from the outside.
Like you can see how the band of the outside of the coin
is smashed inward and the coin gets a lot fatter.
To explain how that works, I'm going
to talk again to Joe Diprima.
He's a member of ArcAttack that you saw the video.
And he's going to tell us how it works.
It's plugged into the wall, which
is coming in at 110 volts.
First it goes to the high voltage power supply.
It's basically a transformer that you
can put in a low voltage at a high current
and you get a high voltage at a low current.
So then this high voltage power supply
charges up a capacitor, which is basically like a battery.
But this one is huge.
It weighs 160 pounds and gets charged up to--
8,000 volts.
It's 8,000?
Yeah, 8,000 volts.
Wow.
Only 72 times higher than your wall electricity voltage.
So then the operator triggers the switch to close.
When the switch closes, two brass balls
get really, really close to each other,
but they don't actually touch.
The voltage potential between that
causes the air to break down.
And the spark that forms between the two contacts
is what actually completes the switch.
Which to me, that's one of the craziest parts of this,
is that the switch is not actually
two metal pieces touching.
They just come close enough that they can break down the air.
Yeah, exactly.
But the reason that we do this is
that if we actually touch those contacts together,
they would just get hot and fuse together.
What?
Yeah, I mean, it would just be like using
a welder to weld pieces of metal together.
So the last step is a bleeder resistor connected
to the capacitor in case it didn't discharge all the way
because for one--
The work coil gets obliterated during the process.
So the capacitor didn't discharge all the way.
And so that bleeder resistor just
makes sure that is no longer a lethal situation.
Disclaimer, this is not a how-to.
There are so many safety features in addition
to what I've included in this video
all the way down to safety switches making sure
that the steel blast chamber is on.
So never, ever try this at home.
So now I'm going to get into how physics does
this, because I love physics.
So you've got your coil wrapped around a coin.
And then you run current through it.
And the current is key.
Because current flowing through a wire
produces a magnetic field.
You get a magnetic field that's pretty much
straight and parallel on the inside of that coil.
And that's where our coin is.
So the quarter will feel that magnetic field.
We can get the computer to predict what the magnetic field
is going to look like.
You use the FEM software to model the coil and the coin.
Yeah, and the initial condition.
The reason why we use FEM to figure this out
is because pretty much every part in the system
is measurable except for the coin.
Right, because during operation it's a very dangerous space.
Yep.
So according to this simulation,
the highest magnetic field density is 18.86 Tesla.
Which is crazy.
It's pretty high.
That's a magnetic field two times stronger
than what you need to make a frog levitate,
and frogs aren't known for their magnetic properties.
Now one of the reasons that our coil doesn't
make a stronger magnetic field is that it eventually explodes.
But before it does so, the current in the coil
ramps up to about 50,000 amps.
50,000 amps is like lightning bolts.
Typical lightning bolts are somewhere around 10,000 amps.
That's an incredible amount of current.
While the current is ramping up in the coil,
that also means its magnetic field is ramping up.
And the thing about increasing or just changing
magnetic fields is that they can induce currents
in nearby conductors.
So some currents start to flow in the quarter.
This is known as Faraday's law of induction.
The current on the coin that I have calculated
should be around 138 kiloamps.
130,000 amps?
Whoa.
The FEM simulation told us what the voltage across the coin
should be.
Oh, interesting.
So we can figure out the wattage
just by saying volts times amps.
What is the voltage in the coin?
So it says that our coin voltage is 192 volts.
So we can figure out the wattage by saying 138 kiloamps
times 192.
Wow, 26,496,000 watts.
Yeah.
That's a lot of watts.
26 megawatts?
That's like two million 10 watt light bulbs.
You could say it like that.
You could say it's x number of toasters or television sets
or whatever.
All right, so you've got this super strong current,
this 100,000 amp current running through the quarter.
And most of that current stays on the outside of the coin.
Now current or moving charges inside of the magnetic field
are subject to a force.
This is known as the Lorentz force.
So you've got that magnetic field produced by the coil
and then you've got these moving charges in the coin, which
because of the direction of the magnetic field,
feel a force inward, making the coin shrink.
That's how it works.
But there's one more side to this coin.
Oh yes, I did.
There's a current moving through the coil as well.
But it's current is flowing the opposite direction.
So it's going to feel a force in the opposite direction which
makes the coil explode outward in a super violent event
with tons of copper shrapnel and vaporized metal.
And it's just crazy town.
So anyways.
There are a number of groups that actually do this coin
shrinking.
There's a group called the National Mag
Lab that does it and they make coins for kids.
There's the group Hackerbot Labs that
let me use the slow motion footage of the coin shrinking.
And then there is that website CapturedLightning.com,
definitely worth checking out.
So thank you so much for watching and learning
all about how we use an electromagnet to shrink
currency.
And I hope you subscribe for more physics.
And as usual, happy physicsing.
One last shout out to ArcAttack and especially
Joe Diprima for having us at their warehouse
and providing so much information for this video.
You can check them out on Facebook
at Facebook.com/arcattack.
And check out their Tesla coils with Joe Hanson on It's
OK to Be Smart.
Links in the description.