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so today and i'm at the University of Sydney with Doctor Phil Dooley 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 Phil: exactly, exactly it was quite a
the landmark historical
experiment
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 high-voltage power supply
so we can suck the air out of here Phil: that's right
and then apply a high voltage two metal plates Phil: yes
Normally with
high voltage in air we don't get anything except maybe a big spark
but what we what Geissler found who did this in 1857
was something quite different so shall we have a look?
Derek: let's do it Phil: ok, let's turn on the pump
and
the high volts
turn off the lights so we can see what's going on
as you can see
something's happening now
yes I see a bit of a pink
glow in there. Phil: that's right so imagine Geissler, the first person
to ever see this, it's pretty surprising
that started people thinking 'what is the stuff that's coming from the cathode?' There seems to be
a ray emitted from this negatively charged one which they called the cathode so therefore
it's called a cathode ray
and it became the topic for research for the next forty years since
all the big big wigs of physics in science basically tried to work at what was going on
So what did they figure out? I mean what is going on? What's producing this glow here
there were two main camps
one thought that it was waves
and the second thought that the electricity was being
carried by a stream of charged particles. Over the next forty years they basically
came to the conclusion - well it was JJ Thomson in eigteen ninety seven
who came up with the idea that uh... there is
a stream of very small charged particles
uh... negatively charged
they're smaller than an atom so the smallest atom
a hydrogen atom
they're about one thousandth of the size of that
and it doesn't matter what material it -
the metal is
it's always the same particle, so this particle appears to be in everything
and this electron as it was as knownn is what's carrying the electricity
so Thomson came to the conclusion that
all atoms have this particle as one of their constituents
that's right, that's right so it wasn't a billiard ball, there had to be something inside the billiard ball
so how do I picture like a billiard ball
with bits inside it? Phil: Well you should probably think about a pudding
A pudding? Phil: Yeah well that's what his idea was, that it was a plum pudding
very dear
to every British person's heart
Derek: right Phil: and inside the putting you have 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 putting
are you a fan of plum pudding?
For research purposes definitely
All right, let's see if we can research this a little further sounds like fun