Hello, Integrated Science class.
So now I want to talk
about how the understanding
of electricity changes.
So Benjamin Franklin had
thought about electricity
as a kind of imponderable fluid.
And if you remember from
our discussions of heat,
that was also how people
in the 18th century
thought about heat at the
time, as a kind of fluid
that they called [INAUDIBLE].
But you'll remember that this
understanding was abandoned
as heat became to be understood
in terms of this broader
category of energy
that gets developed,
and you'll see something similar
happening with the history
of electricity.
So you see the study of it
going from this qualitative
descriptions based on
fluids to a much more
quantitative,
mathematical description
in the 19th century,
and you also
see it going from being this
isolated phenomenon-- that
is, this sort of strange effect
that was study by itself--
to being unified with the
rest of physical forces,
to being part of a much
bigger explanation.
So now we'll head
to France, where
a man name Charles Coulomb
invented a device called
the torsion balance,
which was able to measure
these electrical forces much
more precisely than they've
been able to be measured before.
So the way the balance
works is that there's
a long silk string within this
sort of long glass section
that you can see.
So hanging at the end of that
string, then, would be a rod,
and at the end of the rod
was a little metal ball.
So you put an electrical
charge on that ball.
You could see that there's
another small ball there,
and that one, too, could have an
electrical charge on it, which
would mean that
these two balls would
be sort of either
attracting each other
or repelling each other.
So what Coulomb
wanted to do, then,
was to be able to measure
how much they repelled
each other by
measuring how much,
then, that force was
twisting the string, sort
of what angle that bar
was turning through.
He was able to get very precise
data, and what he concluded
was that the force between
these two electrical charges
was an inverse square law,
much like the force of gravity
that Newton had uncovered.
So you can see the
formula here that I'm
sure you've seen
before in your book.
So the force between
these two charged
walls was equal
to k, a constant,
with the q1, the
charge of one ball,
and q2, the charge
of another ball,
multiplied by one another,
and then all of this
was divided by the square of
the distance between them.
What I want to do next is run
through a series of experiments
that changed the way that
people thought about electricity
and showed that electricity was
connected to things that they
hadn't thought that it
was connected to before.
So the first of these was done
by an Italian, Luigi Galvani,
in 1792.
What he did was he
looked up frogs' legs--
so he took dead frogs,
cut off their legs,
but left the nerve
endings coming out--
and then he hooked up
these nerve endings
to an electrical apparatus.
So what you see here,
you see the wheel
which is used to
sort of generate
a bunch of static
electricity, you
see the sort of
disembodied hand which
is drawing the
electricity off of that,
and then that electricity
is being put onto the nerves
that are hanging out
of the frog's legs,
and what he found when he did
this is that the legs would
start kicking in such a
way that it looked exactly
as if sort of the frog was
alive and kicking its leg.
So what this indicated
to him is that there
was some sort of connection
between electricity
and the processes of life.
This, by the way,
was the fact that
inspired Mary Shelley
to write Frankenstein.
So it has all sorts
of repercussions,
but the one we'll
focus on here is
that it pointed that
electricity was not just
this isolated phenomenon, but
was connected to other things,
like whatever it was
responsible for life.
It was in the 19th
century that people
began to figure out the
electricity was also
somehow related to magnetism.
So magnetism was
this other force
that had been known for
hundreds of years by this point.
People were very familiar
with the lodestone,
as they called it, which was
this stone which sort of always
directed itself
towards the north.
This was the basis of compasses.
People have been using
compasses for a very long time
to help navigate by
this point, but it
only in the 19th
century when they
began to figure out that
electricity and magnetism were
somehow connected.
So the first hint came in 1820
with a Dane Christian Oersted,
and what he figured out is
that if he had a magnet that
was placed near a wire
and whenever he set up
a current that would start
going through the wire,
the needle in the magnet started
to wiggle back and forth.
Eventually, he figured out
that what was going on,
whenever you had a current
going through a wire,
it was setting up this circular
magnetic field around it.
Meanwhile, over in
France, you also
had a French physicist,
Andre-Marie Ampere,
who was inspired to start
working on similar things,
and what he figured out is that
if he had two parallel wires
and he sent currents
through them,
they essentially acted as
magnets towards one another.
That is, they attracted
and repelled one another
the same way that magnets would.
So you have with all this
work a clear indication
that electricity and magnetism
are two separate things,
as had been thought all
along, but actually seemed
to be connected to one another.
So Oersted and Ampere
had figured out
how to use electricity to
create magnetic effects,
and a few years later, an
Englishman, Michael Faraday,
figures out how to do
the opposite-- that
is, he uses magnets then to
create electrical effects.
So what he does is he builds
two large magnetic coils.
You see them over here.
So one is very big and
has a hole in the center,
and the other one is smaller
and actually fits inside.
And so he starts moving this
smaller coil inside the bigger
one, and as long
as those two coils
are moving with
respect one another,
he actually created a
current going through a wire.
So just by having two
magnets moving with respect
to one another, it created
an electrical current.
So this goes on, then, to
be the basis for generators,
transformers, motors.
It really has an enormous
practical component to it,
as well.
