in the early 1700,
the world of science

turned its attention 
to the problem of electricity.

there was 
a good reason for it.

you see, many scientists

actually made their livings
by giving lectures.

either they were
itinerant lecturers

traveling from
town to town,

speaking to whoever
bought a ticket,

or they were
university professors.

either way,they had to
attract an audience.

of course, today,

university professors
 have guaranteed audiences,

but that's because
of the required course,

which was
a much later invention.

to attract an audience,

they wanted flashy,
exciting demonstrations,

and electricity
was just perfect for that.

a typical demonstration

was to get a street urchin,
a little boy

they would string him from
the ceiling by silk threads,

charge him up

with an electrostatic
charging machine,

and draw sparks
from his nose.

i wanted to show you 
that demonstration,

but all the street urchins
were tied up.

I'll have to make do
with these things instead.

first i'dlike to
explain to you
a few simple principles
of electricity.
I'm going to show you

some unusual things.

at first glance,

the teaching scientist
and the performing magician

seem to have little in common

fee; free to count them

and yet there's no doubt

that each could learn a few 
good tricks from the other.

the two black kings...

across the stages of history,

whether one practiced science
or sorcery

often depended on
the observer's point of view.

that's exactly halfway down
in the pack.

to find that card,
i cut off half the pack.

no matter whether it was
pure science or pure mischief,

the ancient Greeks
pursued it with a passion.

the Greeks were quick
in sport and science alike

and made a startling discovery
early on

about the nature
of electricity.

it's a wand
made of rosin.

i rub the rabbit...

certain materials
act like a magic wand 

when rubbed against 
a rabbit's fur

and attract
small bits of matter.

eventually,scientists would
be able to explain

exactly how this phenomenon,
electricity,really works.

and,unlike
the professional magician,

the early electricians
were willing

to share the secrets
of their trade.

for instance,
one of the keys to electricity

hasn't been a secret

since Benjamin franklin
tried his hand in the field

he spread the word,

and in simple English,
this was it--

something called charge,
theelecturic force.

that was brilliant
as far as it went,

but what was the connection
between charge and force?

in science,as in magic,

timing is everything,

and in France,
Charles Augustin Coulomb

appeared with the answer.

Coulomb's experiment,

which revealed the relation
between charge and force,

could be verified
by other scientists,

and,most convenient of all,

it cold be described
in simple mathematical terms.

Coulomb's states
 that the electric force

is proportional to
the product of the charges

and inversely proportional

to the square of the distance
between the charges.

furthermore,there are
two kinds of charges--

positive and negative.

electricity attracts
when it acts between charges
of different signs.

but acting between charges
that are the same,

it repels.

according to
Coulomb's lan...

the force two charges
exert on a third

is the vector sum of the forces
each alone would exert.

in fact ,the force from
any number of positive charges

and negative charges

add together as vectors,

so the total force is still
calculated from Coulomb's lap.

notice that positive charges
are shown is red,

and negative charges
are shown is blue.

electric charge both exerts and
experiences the electric force,

and the electric force
obeys couloumb'slaw.

it looks as simple

as an18th-century
electrical device,

and on the surface,
that's all there is to it.

but electric charges
don't exist in isolation.

instead,electricity
resides in matter--

the solids,liquids,
and games of the universe.

and no matter the from
it comes in--

solid,liquid,or gas--

matter itself is essentially
electrical in nature.

so,to understand electricity.

one must first
come to terms with matter.

on the other hand,
to understand matter,

one must first grasp
the essentials of electricity.

in fact, neither can 
be understood without the other.

in his own study,franklin began
by thinking of electricity

as a fluid in some combination
with matter

if there was too much fluid,

he imagined matter

to be positively charged
with electric fluid.

if there was too little fluid,
he imagined the matter

to be negatively charged
with electricity.

therefore,in franklin's mind,
matter was in its proper state--

that is, electrically neutral
and balanced--
only when the right amount
of electric fluid is present.

franklin was the first

to see electricity
in positive and negative terms.

but rather than visualize

two different kinds of charge,

he saw either too much
or too little

of the same electric fluid.

in the right hands,

franklin's single electric fluid

became two kinds

of electric charge.

they vanish into the cup.

by accumulating knowledge 

piece by piece,

scientists would put it

all back together

as asingle structure

whose basic

building block are atoms

held together by positive
and negative electric charge.

at the care of every atom
is a nucleus

which is made up
of protons and neutrons.

protons contain
its positive charge.

the atom's neutrons
have no charge.

which  means
they're electrically neutral.

the nucleus as awhole
is surrounded by electrons,

which have negative charge,

and on the whole,
each neutral atom

has the same number
of protons and electrons.

the positive charge
of each electron,

and they're bound together

by the attractive
electric force between them.

they vanish into the cup
quite mysteriously.

when they reappear...

but this rather special
balancing act,

like any other act,

is sometimes 
less than perfect.

as a matter of fact,
not all atoms are neutral.

some have too many electrons or too few,

in which case
they're called ions.

in fact, sodium ions
with a net positive charge

and chlorine ions

with a negative charge

are bound together
by the electric force

into crystals that make up
ordinary table sale.

but whether their atoms
are ionized or not,

solids,liquids, or gases--
all matter in the universe

is bound together 
by the force of electricity.

for instance, they  could take
this dull copper coin..

and of all the forms
of matter,

none exhibits
the effects of electricity

more clearly than metals.

...into solid gold.

gold...

the stuff that dreams
are made of.

throughout the ages,

scientists have dog deeply
into the nature of metals,

and in their quest,

they've found that all metals
have similar every metal

for one thing, every metals
is malleable and ductile,

having the capability to

change shape without breaking.

another age-old property
is luster,

the degree to which
a shiny metal reflects light.


for a long time,
that was it.

but in the1700s,

scientists found
another property

common to all metals.

today,it'scalled
conductivity,

the ability to
conduct electricity.

on an insulator,

an electric charge
stays where it is.

but on a metal
conducts electricity.

on a deeper level,
this is what happens.

each atom of a metal can be 
thought of as a positive ion

with two metallic atoms
are very close together,

the outermost electrons can pass
easily from one to the next.

as more atoms are added,

electrons can range
farther afield.

those mobile electrons are known
as conduction electrons,

and they give metals
their special properties,

and they give metals
are electric conductors

because every metal is like
a giant molecule

in which a number of electrons
are shred equally

by all the atoms.

picture it as a fluid
of positively charged ions

glued together by a fluid
of mobile electrons.

if attracts the mobile,
negatively charged electrons

toward itself,

causing them to pile up
at the nearest surface.

the result is to leave
net positive ions,

unbalanced by electrons,
at the far surface.

the closer an electric charge 
gets to a metal,The more charge of the opposite sign

builds up on the near surface

and more charge of the same sign

is left on the rest of the surface.

And now an amazing little box!

These properties are used in an instrument of science

that may seem like magic.

It's called a GOLD-LEAF ELECTROSCOPE.

When an electric charge is brought near the metal disk,

The gold leaf moves away from the rod.

Float!

A positive charge near the top attracts negative charges,

leaving positive charge at the other end of the metal rod,

and the gold leaf is left with the same kind of charge.

And, of course,

with the same kind of charge,

the rod repels the gold leaf.

When the wand is removed, the leaf falls back down

unless charge is transferred to the disk

by physical contact.

Float.

Stay.

Physical contact leaves the rod and gold leaf

with a net excess charge, 

and the leaf stays up.

But it falls again at a touch of the hand.

Down.

The hand, which is itself a conductor,

connects the post to the electroscope case.

Where on earth did that extra charge go?

The electroscope case is in contact with the earth,

which is a very big conductor in its own right.

When contact is made, 

the electroscope, like any other conductor,

shares its charge, releasing most of it into the larger body.

Although in reality only negative electrons

flow from one place to another,

The effect is exactly as if positive charge flowed

in the opposite direction.

This is called grounding an electric conductor,

or simply grounding.

And for all practical purposes, when it happens, 

the conductor becomes electrically neutral.

If that's the case, 

how dose anything ever get charged in the first place?

One way is friction, which is no surprise to anyone 

who's walked across a day carpet and received a shock.

But there are more effective ways 

to charge by friction.

I've built up a static charge 

so that the paper clings to the rod.

In the 18th century, electricians devised machines

that accumulated electric charge by rubbing a spinning insulator,

such as glass.

And now a little something you'll find electrifying.

This is courtesy of my good friend Mr. Van De Graaff.

In the 20th century,

Robert Van De Graaff used the same principle--

charges stay put on the surface of an insulator-- 

to come up with a new twist.

Down here, an insulating belt picks up electric charge.

The conveyor belt carries the charge upward 

to the top of the machine,

where the charge is transferred to the inside of the metal dome.

Since metal is a conductor, the charge spreads out 

and, in the process, builds up

until it escapes by means of a spark

and makes its way back to its old home, the ground.

But Van De Graaff'smachine had much more potential

than a mere trick 

to spark the interest of a cabaret audience.  

In fact, its main feature--

transferring electric charge by conveyor belt--

in the principle behind one of the most important devices

of the modern nuclear physics laboratory.

This sturdy yellow chamber,

by containing gas at high pressure,

is designed precisely to prevent sparks from flying.

Inside, with no sparks to discharge it, 

an enormous positive charge is built up by conveyor belt

on the main terminal at the center.

In the meantime, a negatively charged ion--

in this case, a carbon atom with an extra electron--

is being prepared for an extraordinary journey.

Started  on its way by other negative charges...

steered around a corner by one magnetic field,

and kept at the center of the tube

by another magnetic field, 

it soon feels

the attractive force  

due to the positive charge on the main terminal.

Accelerated by the electric force 

between the negative ion and the positive terminal,

the ion streaks forward at high speed

until a collision with gas atoms strips some electrons,

changing the ion from negative to positive.

Accelerated once again by the electric force,

the ion continues on to its destiny, 

in this case, a nuclear collision

between carbon and a target of helium.

This extraordinary machine is called 

Tandem Van De Graaff Accelerator

because it uses the enormous charge

built up by the Van De Graaff generator

not once, but twice.

Of cause, using the positive charge twice

is a trick of sorts,

but it's still strictly science,

not magic.

Although Robert Van De Graaff's conveyor belts

are an excellent way to build up charge,

mother nature's always had a few tricks of her own 

along those lines.  

Since the beginning of time,

Thunderstorms have involved huge build-ups and releases

of electric charge.

Scientists believe the mechanism involves friction

between ice particles in the clouds.

But friction isn't the only way charge can be transferred.

This metal plate seems to be charged

just by touching it.

It's not magic,

but there is a trick to it.

If a positive charge is brought near a metal,

negative charge will rush toward it,

and positive charge is left behind on the other side.

Then, if the metal is momentarily grounded,

charge flows between the metal and the earth,

leaving the metal negatively charged

when contact is broken.

but if I charge the stand...

You'll notice an incredible reaction.

That principle's called charging by induction,

and it can seem magical to an audience

that doesn't realize there are electric charges

trapped inside the plastic sheet.

That's why the metal plate seems to have been charged

just by touching it.

The trick is that touching the plate 

momentarily connects it to the ground,  

and that's what leaves it electrically charged.

This is not H.G. Wells' time machine.

It is instead known as the wimshurst generator,

one of several early ways of making electricity.

Watch closely. 

Invented in 1800 by James Wimshurst,

an English engineer, 

this flashy machine features counter-rotating disks 

on which metal tabs are charged by induction, 

with contact being made and broken

through metal brushes.

As the wheels rotate, electric charge builds up

until a miniature bolt of lightning
        
relieves the mounting tension.

One of the secrets of the wimshurst machine's success

is the device it uses to store up electric charge. 

It's the Leiden Jar,

named after its birthplace at the university of Leiden.

The principle behind the leiden jar

is as simple as the device itself.  

In a leiden jar, the inside and outside are metals,

separated by the glass of the jar.

If the inside is charged while the outside is grounded,

the net result is equal amounts of opposite charge

on both sides of the insulator,

and those opposite charges are held firmly in place

by the electric force between them.

The leiden jar was one of the best tricks 

of the 18th-century electricians,

who were often accomplished performers.

Of course, the modern magician has a few tricks of his own,

and the magician's tricks illustrate, above all,

the greatest difference between magic and science.

The magician's art is to 

confound the senses

and create mystery,

but the scientist's task is to expand the senses

and solve mysteries.

A live hair!

If this disappointed you, maybe I can transform it 

into the kind of hare you were expecting.

Nevertheless,

magicians do have one thing in common 

with the modern professor.

Ladies and Gentlemen, a live hare!

They both try to entertain,

at least, to the best of their abilities.

I wanted to show you 

that electricity can actually be useful,

so when my young friend here said she wanted her hair teased,

I thought maybe I would do it on this Van De Graaff machine.

This won't hurt a bit.

There we go.

Watch what happens 

when I turn it on.

You see that? 

Electricity can be absolutely hair-raising.

She wanted to known how much this would cost.

I told her when I was finished, there'd be no charge.  

This is a different kind 

of electrostatic generating machine.

It works by induction

and by making and breaking contacts.

But its basic purpose-- 

its purpose is to throw sparks.

I thought they were going to give me an electric motor

to run this thing,

but when I read the fine print in my contract,

it said I had to crank it myself.

There you go.

It's a lightning machine.

It's actually quite dangerous.

If I grabbed the wrong thing at the wrong time,

you could lose a professor or, at the very least,

learn a few words that aren't in the curriculum.

The biggest machine of this kind ever made 

was made by a Dutch physicist named Van Marum.

Long before the work of Wimshurst and Van De Graaff,

back in the 1780s, and 1790s, Martinus Van Marum, in Holland, 

experimented with the largest electrostatic generating machine

ever made.

It had been built for Van Marum 

by an English instrument-maker named John Cuthbertson.

Van Marum's giant machine used a bank of 100 leiden jars.

Its rotating disks were over 6 feet in diameter,

and it could hurl a lightning bolt 

a distance of more than 2 feet.

It was a kind of electrostatic dinosaur,

the end point of evolution

of the 18th-century electrostatic

generating machine,

and in a few years, it was extinct

because in Italy, Alessandro Volta

had invented a far more elegant and useful device,

one that would take electricity into a new era--

the electric battery.

We'll get to the electric battery soon,

but first I'll tell you about another new idea--  

the electric field.

We'll do that next time.

Captioning is made possible by the Annenberg/cpb project

captioning is performedby the national captioning institute, inc.

Captions copyright 1987 California Institute of Technology,  

the corporation for community college television, the Annenberg/cpb project

public performance of captions prohibited without permission of national captioning institute

funding for this program was provided by...

the mechanical universe is a college course 

with textbooks published by Cambridge university press.

For more information about the course,

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