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At this point

Wefve learned a lot about electricity

We know about forces and charges and voltages

and electric currents and so on,

and the question arises,what's all that stuff?

what's really important about all that stuff?

let me give you an example.

remember van marum's giant machine

that was made at the end of 18th century.

it could develop a voltage of 100,000 volts.

it used a bank of 100 leiden jars to store energy in,

and it could store 2,000 joules of energy.

and so the question is, is that impressive?

and the answer is really no.

2,000 joules of energy

is about 1/2 of 1 food calorie.

or to put it in pruely electrical teams.

this little 9-volt transistor radio battery

can atore 10 times as much electrical energy

as van marum's bank of 100 leiden jars,

and yet, that machine could hurl a lightning bolt

a distance of 2 feet,

and the battery certainly can't do that

and so the question is, what really is important?

voltage, or electric potential,

such as, for example,

the electrons that make up the atoms in your body.

you might ask the question,

what is the potential binding electrons to your body?

it better be much more than ican develop with that machine

because if it isn't,

the machine would be devestatingly dangerous.

it could rip us to shreds.

so, are electrons bound to your body

mach more strongly

than I can develop a potential with that machine?

the answer is no.

the binding potential of an electron in your body

is only 3,4,5 volts

I can develop 100,000 volts with that machine.

once again, we've left with confution

about what's important in electricity

the basic elements of electricity are very simple.

if I can imagine point electrical charges

in a vacuum,

then there are positive charges,

and they attract or repel each other

with a force that varies inversely

as the square of the distance between them.

that's all it is,

and yet it took thousandas of years

to figure that out.

even today,wheb we understand it well,

it's still confusing to learn.

the reason that's true

is because these elements of electricity,

point charges in a vacuum,

never exist in the real world.

electricity always exists in matter,

and so in order to understand electricity,

we must first understand matter.

but matter is essentialy electrical in nature,

and so in order to understand matter,

we must first understand electricity,

and that's the crux of the dilemma

that we want to speak about today.

at first glance,

tylying to see electricityin its true light

seems as risky as a night out on the las vegas strip.

electricity has numerous quantities

change,potential,and field,to name a few

and with such a bewildering variety,

it's hard to know which quantity to bet on.

what's needed is a way to explain

how everything fits together,

a way to stack the deck

in faver of good sense and clarity.

what's needed is a sure-fire method behind this madness,

the cause behind the effect,of electricity.

what's needed is a change of scene.

on the surface,the electrical connection

between las vegas and these nevada hills

isn't immediately obvious.

for one thing,surveyors don't ganble.

there's nothing random

in the detailed presition of their maps,

nor in their measurements

that determine the height above sea level

of each point on a predetermined grid.

a line is drawn,cinnecting all points

a certain height above sea level

and then repeated for other heights

at regular intervals.

to a practiced eye,

the resulting contours of constant height

give a clear representation of the real landscape.

by the same token,

the contours on this map

give a clear representation of an electric field.

these are contours of constant electric potential

that has its ups and downs.

when real ground gose up and down,

the prudent traveler wants to know about it

because  going uphill can be hard work,

and exactly the same is true for electric potential.

moving up the incline of potential is hard work.

and the steeper itis, the harderit is climb.

of caurse, if the potential isn't changing,

it takes no work at all,

and if the potential decreases,

the field is downhill all the way.

in this analogy,electric potential is elevation,

and electric field is the downward slope,

to put it in more mathematical terms,

the electric field is a negative derivative

of the potential

or,in other words,

the potential is manus the integral

of the electricfield.

the electric field of a single point change

is proportional to 1/r-squared.

so its integral is proportional to 1/r.

foe a single point change,

the direction of the field is pretty obvious,

but what about more complicated situation?

what does the electric field for this potential look like?

because it takes no work to move a change

along a curve of constant potential...

there's no component of field in that direction.

so the field is perpendicular to each equipotential

at every point

and that's how is assumes its familiar shape,

the familiar shape of even  the most rugged terrain

isn't all peaks and valleys.

some regions are perfectly flat and horizontal.

a lake is a region

of constant height above sea level,

jast as a region of constant electric potential

is created by a conductor in an electric field is always perpendicular

to that surface.

out in the hills,it's hard to find much

that's perpendiclar to anything,

but in the city,it's easy.

here it's easy to find electricity at work and at play.

although this proliferation of light and color

is probablynot what the poineersof electricity

had in mind

they nevertheless laid the foundation for it.

Ben Franklin did his part by bringing electric potential

out of the heavens and down to earth.

Thomas Edison,thinking more about work than play,

captuned electricity is glass an made it yield light.

the eventual proliferation of neon sings

was probaby not even imagined by georges claide,

the french physicist

who developed a practical neon light in 1909.

those first neon lights

were put to work in the grand palais in palis,

not as decoration,but as houselights.

the reddish glow of those lights

was seen as a drawback by everyone,

everyone but jacques fonseque,a publicist.

in that red glow,he saw great possibilities.

he persuaded claude to sell him the rights,

and by 1912,

paris had the world's first neon sign,

and the work had barely begun.

electric potential is the ability to do work

by making electric charges flow,

and no matter where they go,

their potential

is measured in volts.

but how big is a volt?

and how many volts does it takes

to do a job?

a flashlight battery is rated at 1 1/2 volts.

with only 2 of them,

one can do work worth millions.

when necessary,

12 volts is enough to start the getaway car,

and 110 volts,enough to light a bulb or two,

or send a crock fleeinginto the night.

however,crime doesn't pay.

even with a one-armed bandit,the game can go too far.

[gunshot]

when that happens,nobady wins.

non august 6,1890,at 6:40 a.m.

at auburn state prison,new york,

Mr.William Kemmler was the first person in the world

to die by electrocution.

it took approximately 17 seconds

and several thousand volts,

but the electric chair

wasn't the first use of high voltage.

in the 18th century,

van marum's giant electrostatic generator

could generate100,000 volts.

so could the smallerand the van de graaff
    generator,

and in the modern
physics laboratory,

this tandem van de graaff
particle accelerator

uses 3 million volts.

But high voltages

are not confined
to exotic laboratories.

Every day, power lines
carry electricity

at hundreds
of thousands of volts

to do their work,

and part of that work
is to hold this town together.

Occasionally, they even 
help bind people together.

But electricity
is also responsible

for an altogether 
different type of binding.

The atom itself,

the basic building block 
of everything

we see, feel, or smell,

is held together 
by the force ofelectricity.

And that bond between 
the electron and the atom 

has a definite voltage

That boltage
holds the world together.

And so what is the voltage
of the atom itself?

In every atom,

the electric force binds
negatively charged electrons

to a positive nucleus.

The nucleus is so small,

it can be thought of
as a point positive charge,

even though it really consists
of neutrally charged neutrons

and positivelly charged
protons.

To balance the positive charge
of one proton.

The result may be
a perfectly neutral atom.

This picture,
or any picture of an atom,

is only a model,

but as a model,
it is a guide to fact,

and one such fact
of great importance

is that the distance
from the nucleus

to the outermost electron 
of any atom

is always 
about 1 angstrom unit,

100 millionth
of a centimeter

from the point of view
of that outermost electron,

the other electrons virtually
balance the electric charge

of all the protons 
in the nucleus except one.

So, the outermost electron

detects very nearly
the electric field,

and the electric potential
due to one proton,

about an angstrom away.

It's electric potential
works out to just a few volts.

And because its charge
is negative,

so is its potential energy,

conveniently measured in units
called electron volts.

Those few electron volts,
minus a little kinetic energy,

is what has to be overcome
to tear an electron

from an atom.

About the same is needed

to remove an electron
from a molecule

or from a hunk
of solid metal.

Considerably less
has to be overcome 

to tear dollers away
from las vegas tourists.

While the gamblar's attraction
for money is great,

the bond between any one doller
and the gambler

is very slight indeed.

But some of the other bonds
made here

are more long-lasting
in nature.

At least in some cases,
the tie is very strong.

But when a few volts
tie an electron to an atom,

how strong is that bond?

Since a van de graaff generator
can build up 100,000 volts,

it seems this machine 
ought to be capable of ionizing

every bit
of ordinary matter in sight,

but it isn't. 

Sometimes,
voltage alone isn't enough.

In fact, in an atom
and a van de graaff

engage in a simple tug of war
for one electron,

the atom always wins

because a tug of war 
is a question of force,

not voltage.

In other words,

what matters is the derivetive
of the potential energy,

not just how big it is.

Here's a van de graaff dome
and an atom.

They're competing
for an electron

that might be bound
to the van de graaff

by tens of thousands
of volts.

But zooming in by 10,

100,

1,000 times,

the electron's potential energy
due to the atom

is seen to be much smaller,
but very much steeper.

In fact, the horizonal scale
has to be expanded 10,

100,

1,000,

10,000,

100,000 times
just to see the slope.

The atom's force
is 100,000 times stronger

than the van de graaff,

and that's
no contest at all.

And it's not much 
of a contest

when the house
ditermines the odds.

That's why the smart players

prefer to leave
little to chance.

Benjamin Franklin
was such a person.

He even found a way

to take some of the risk 
out of thunderstorms,

and in fact, his invention
of the lightning rod

spared many a church,
barn, and home

from framing destruction.

mthundern

Where does the light
in lightning come from?

As in any spark,

the molecules of air
are momentarily ionized,

leaving a gas
of positive molecular ions

and negative electrons
called a plasma.

very quickly, the electric force
between ions and electrons

causes them to recombine
into neutral matter,

giving off their excess energy
in the form of light.

But lightning can be tamed.

in a neon tube, 
for instance,

the same process can be slowed 
to a continuous glow.

But the electric field
in a neon sign

or avan de graaff machine
or even a storm cloud

can't ionize matter.

So how do they 
cause sparks to fly?

The answer is that

but not in a direct 
tug of war.

The air around 
the van de graaff bulb

always contains 
a few accidental electrons.

The electric field
of the van de graaff

accelerates such an electron
until it hits anothor molecule.

Then it starts over again.

If the distance between atoms
is large enough

and the field is strong enough,

the electronscan build up 
enough kinetic energy

to knock another electron off 
when it hits.

If that happens,
both are accelerated,

causing more ionization

in a chain reaction
that creates a spark.

So, a van de graaff machine 
or a neon sign

ionizes the air
not by sheer electric force,

but by collisions.

While that's 
not exactrly cheating,

it's a trick, nonetheless.

But then,
this town's full of tricks,

tricks of the trade 
scientifically designed

to ionize
the tourists' pocketbooks.

It's also full of energy,

and the energy of the people
seems to rise by the hour.

Electric energy,
on the other hand,

goes up with voltage
and with charge.

So, the question
of how much energy

an electric device
can deriver

depends not only
on its voltage,

but also on how much charge
it has available.

The van de graaff

and this giant 
electrostatic generator

both reach very high voltages
before sparks discharge them.

But even van marum's
100 leiden jars

couldn't store
nearly as much charge

as there is
in an automobile battery.

Even though it has
a far lower voltage

than those machines,

it stores so much charge 
in chemical form

that it's vastly 
more useful.

In fact,
a common radio battery

stores 10 times the energy
of van marum's generator.

A battery
is a storehouse of energy,

but on any given day,

despite any given number
of batteries,

much more energy
is actually stored right here.

Yet only a small fraction

of this water's
vast potential energy

is converted 
to electrical energy.

That energy
travels across the desert

to the city,

where it's radiated
into the night

in all colors, 
shapes, and sizes.

But behind
the glittering facade,

charge and field,
energy, voltage, and force

are the stuff
of electricity,

and that's the stuff that holds
the universe together.

At the begining 
of the 1800's,

a British chemist
named John Dalton

propsed the law of simple
and multiple propportions,

and that law,
for the first time,

give a solid,
scientific foundation

to the ancient idea
of the atomic theory of matter.

But not all scientists
accepted Dalton's theory.

Throughout the century,

there was a group
of conservative chemists

who essentially thought
that it was bad science

to believe in anything
you couldn't see.

Of the atomic theory
they said,

"we don't need
that hypothesis."

they weren't
the only ones

who didn't believe
in Dalton's theory.

Dalton's had a rival
for the title

of greatest chemist
in England.

His name
was Humpherey Davy.

Davy didn't believe
in Dalton's theory either,

but his reason 
was the exact opposite.

He thought that Dalton
hadn't gone far enough.

His augument
went something like this.

He said, "There are
40 chemical elements

"that we know of.

"That means that according
to Dalton's theory,

"there must be
40 different kinds

"of indivisible atoms

to explain the properties
of those elements."

"But," he said,
"of those 40 elements,

"26 are metals.

"They all share
the same properties

"of shiny surfaces,

"good electrical
and thermal conductivity,

"mechanical ductility,
and other properties.

"Those can't be accidents

"that just happened
26 separate times.

There must be some underlying
principle of metalization."

That is to say,

Dalton's atoms
must have some inter structure.

It took 100 years,

but it turned out
in the end

that both Dalton and Davy
were right.

Matter is made of atoms,

and atoms do have 
an inner structure,

which explain
why metals exist.

But long before
that was understood,

In fact, even before the time
of Davy and Dalton,

all of it was made use of 

by a wily Italian 
named Alessandro Volta,

who invented
the electric battery.

And that's our story
for next time.

Captioning is made possible by
the Annenberg/CPB project

captioning performed by
the national captioning
institue,inc.

Captions copyright 1986
California institute
of tecnology,

the corporation for
community college television,
and the Annenberg/CPb project

public performance of captions
prohibited without permission of 
national captioning institue

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was provided by

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