Do you want to touch it after I charge it up?
Yeah.
Really?
Yeah!
You'd just do it?
Yeah!
OK.
Go for it.
Go, go, go-- before it leaks off!
Hi.
I'm Diana.
You're watching Physics Girl, and we're
going to show you how to make a 200,000 volt capacitor.
The one that she made me burn my finger on.
It didn't burn your finger.
No, it didn't burn.
Come on.
But it sounded a lot more dramatic.
It was-- it didn't hurt.
I mean, I didn't have to do.
This is a DIY homemade capacitor.
We first created a wand by taping wire to a cake pan.
We made the end of the want with giant round screw,
with a spherical neodymium magnet on it,
a plastic washer for a spark gap,
and smaller metal ball on top--
threaded all of that through PVC pipe,
placed polycarbonate on the cake pan, cut a smooth circle
from a metal sheet, taped that to the bottom of a metal bowl
with the conducting metal tape, put the bowl
on top of the polycarbonate, taped it all together,
and viola!
OK it's done.
It's done!
It's done.
Now what?
Now you can charge up the bowl by rubbing a paper
towel wrapped around a long PVC pipe,
with some insulating grip from foam and a t-shirt,
and then discharge it with the wand,
to create a spark like this.
That is the contraption Ashley agreed to touch.
You seriously-- you have to just go for it, though.
Because--
I know!
Because if you go slowly--
I'm not going to look!
--it's going to make it fizzle.
I'm not going to look.
Just like--
Should I do my pinky or my index finger?
Whichever one you think will hurt the most.
Ha, ha!
Go for it.
Go, go, go, before it leaks off.
[LAUGHING]
But you touched it.
I bet there's still some on there.
Oh!
[LAUGHING]
The reason the spark doesn't look as epic when Ashley touch
the bowl is mainly because she's not
connected to the lower plate of the capacitor like the wand is.
What we made here is a capacitor.
What's a capacitor?
Well, if charges are like cars, then a capacitor
is like a parking lot.
It's like a tiny battery.
But this is not small, you say.
Well, it would only power a light bulb
for a fraction of a second.
So by that measure, it's tiny.
Our capacitor is two metal plates--
the cake pan on the bottom and the metal sheet on top,
connected to the bowl, separated by polycarbonate or Teflon
or some other dielectric.
We charge up the capacitor by dumping charge onto the bowl.
The charge spreads out, and onto the sheet metal
too-- because metal is a conductor.
And like charges repel, so they spread out where they can,
you know?
Like fancy cars taking up lots of space in the parking lot.
Keep charging up the metal, and eventually charge
starts leaking off, because it gets too crowded
with those like charges.
That's why we have the lower plate,
and the dielectric material in between.
The lower plate gets an induced positive charge,
which acts to kind of hold more negative charges
on the top plate, because it pulls on them.
And the dielectric is a magical material.
Inside a dielectric, polarized molecules
get aligned with the electric field
caused by the charged plates.
So it gets its own electric field going,
and then passes along its electric pull,
keeping more charges on the top and bottom plate.
But the dielectric itself doesn't allow
any charges to flow through.
So it's like a store next to the parking lot that
keeps the cars there for its great discount sales,
but doesn't actually let any cars drive-through.
So then we can build up enough charge
that the high voltage breaks down air.
And the charges leap through the air,
and we see that as a giant spark.
After many days of trying, the length of our longest spark
was 10 centimeters-- which tells us we
built up to 200,000 volts on the ball
as a conservative estimate, because the dielectric strength
of air is about 30,000 volts per centimeter,
depending on humidity and temperature and so forth.
But this was after many days of trial and error.
The PVC pipe is an insulator.
So one of the key differences between an insulator
and a conductor is that when were creating charge
on the insulator, the charge doesn't move around evenly.
It kind of stays put.
Yeah.
So when we were first trying it,
we were just trying to rub the PVC pipe
and get that charge build up, and then
just tap it to the bowl.
But it's only going to pass the charges from that one
little area that touched the metal.
You need to touch the entire PVC pipe across the metal.
I was going to wait to tell you on camera,
but I told you earlier, that I deleted
like all of the footage.
Ugh!
We did this for three days!
Yeah, we did this for three-
You deleted all three days of footage?
I mean-- two out of three.
This contraption--
Yeah.
[SHOTGUN COCKING NOISE] So first, we just had this.
And we realized that as we were charging it up,
we were hearing a lot of static electricity being built up,
but we also felt on our arms.
And first, we were like, wow, that's cool.
My arm hair is standing up like a porcupine.
This foam wasn't a very good insulator.
So the help that, we wrapped this piece
of fabric around, which did the job.
So you watched us make an awesome capacitor.
I definitely encourage you to try this at home.
It was super fun to go through the process--
to get the materials, to test things out,
to fail for four days.
[SPARK NOISE]
Ugh.
[SPARK NOISE]
No.
[SPARK NOISE]
Oh, man.
[SPARK NOISE]
Ooh.
Add that to the things that hasn't worked for us.
[SPARK NOISE]
That wasn't as big.
It wasn't as big.
Day three.
[SPARK NOISE]
Whoa.
Whoa-ho!
[SPARK NOISE]
Whoa!
OK.
Well, that didn't work like you expected it.
Meh.
That's disappointing.
But then, watch Ashley get shocked.
Best part.
Yeah.
I'm pretty pleased.
Honestly, what was fun was literally
like the trial and error.
It was very maybe like fifth-grade-science-project-y.
No, honestly.
Like--
Yeah!
No, it was--
--you know what I mean?
Like siblings, cousins, neighbors, doing a science
project--
like this is this going to get you first place.
Yeah, thank you for watching this video,
and come back for more physics.
Hey, if you liked this video, hit the Subscribe button--
and also the little notification bell next to it,
so you're updated when I have a new video.
And the physics-ing.
!
Hey!
So right now, with me right here,
I have Matt from PBS Space-time--
Hey guys.
--which is an awesome show.
You should definitely check it out.
I've got a link to the description,
and in the cards somewhere.
Well, Diana, thank you for having me on Physics Girl.
This is amazing.
You know, Matt, one thing I really like about your show is
that you go really in-depth on topics.
Like you don't hold back.
There's the great series of videos
that have on different quantum mechanics topics.
You know, one thing I really like
about Physics Girl is it explains complex stuff
in such understandable ways--
I try.
--using such simple language.
But I'm a kind of jargony kind of guy.
I love those long sciency words.
But it's hard to keep track of them sometimes,
so I have a challenge for you.
OK.
I would love you to do an episode in which you
explain the five most jargony and commonly encountered
modern physics words in simple English.
Done.
But I want you to use only the 1,000 most
common words in the English language to do that.
That's going to be a little harder.
Yeah.
But challenge accepted.
Keep watching Physics Girl, because we're going
to hold you to this, Diana.
[MUSIC PLAYING]