Kind: captions
Language: en
So today I'm at the University of Sydney
with Dr. Phil Douly and we're talking
about how our idea of the atom changed
from a tiny little hard sphere to
something more complicated and this
apparatus has something to do with that.
Exactly. Exactly. It was quite a quite a
landmark historical experiment. Uh it's
just made of a tube of glass connected
to a a vacuum pump. And in the tube of
glass, there are two pieces of metal
connected to a high voltage power
supply. So
Okay. So we can suck the air out of
here.
That's right.
And then apply high voltage to two metal
plates.
Yes.
Okay.
Normally with high voltage in air, we
don't get anything except maybe a big
spark. But what we what uh Gistler found
who did this in 1857 was something quite
different. So should we have a look?
Let's do it. Okay, let's turn on the
pump and the high volts.
Um, turn off the lights so we can see
what's going on. As you can see,
something's happening now.
Yeah, I see a bit of a a pink glow in
there.
That's right. So, imagine Geistler, the
first person to ever see this. It's
pretty surprising. That started people
thinking, what is this stuff that's
coming from the cathode? Seemed to be a
ray emitted from this negatively charged
one, which they called the cathode.
Therefore, it's called a cathode ray.
And it became the topic for uh research
for the next 40 years as all the big big
wigs of physics and science basically
tried to work out what was going on.
So, what did they figure out? I mean,
what is going on? What's producing this
uh this glow here?
There were two main camps. One thought
that it was waves and uh the second
thought that the electricity was being
carried by a stream of charged
particles. over the next 40 years they
basically came to the conclusion well it
was JJ Thompson in 1897 who came up with
the idea that uh there is a stream of
very small charged particles negatively
charged they're smaller than an atom so
the smallest atom hydrogen atom they're
about 1,000th of the size of that and it
doesn't matter what material it's the
metal is it's always the same particle
So this particle appears to be in
everything. Um and yeah, this electron
as it was as it was known is what's
carrying the electricity.
So Thompson came to the conclusion that
all atoms had this particle as one of
their constituents.
That's right. That's right. So it wasn't
a billyard ball. There had to be
something inside the billyard ball.
So how do I picture like a billyard ball
with bits inside it? I mean,
well, you should probably think about a
pudding.
A pudding.
Yeah. Well, that's what his idea was.
That it was a plum pudding. very dear to
every British person's heart
that uh and inside the pudding you have
uh plums and plums can come out of that.
So when you apply high voltage then a
negatively charged electron which
Thompson pictured as a plum comes out
and leaves behind positively charged
pudding. Mhm.
Are you a fan of plum pudding? Uh
for research purposes definitely.
All right. Well, let's see if we can
research this a little further.
Okay, that sounds like fun.