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[DRUMROLL]

[APPLAUSE]

I THOUGHT IT WAS TIME
THIS CLASS HAD SOME CLASS.

ACTUALLY, THESE DAYS,

SCIENTISTS ARE
PRETTY INFORMAL PEOPLE.

IT'S CERTAINLY RARE
TO SEE ONE DRESSED LIKE THIS.

BUT IN THE 19TH CENTURY,

IT WAS NOT UNCOMMON
FOR FORMAL LECTURES

TO BE GIVEN
IN FORMAL ATTIRE. 

THERE'S NO PLACE
THAT THAT WAS MORE TRUE 

THAN AT THE FAMOUS
ROYAL INSTITUTION

‡T HAVE A PICTURE
THAT WAS MADE

IN THE MIDDLE
OF THE 19TH CENTURY.

THIS PARTICULAR PUBLIC LECTURE

SEEMED WORTH IMMORTALIZING
IN A PICTURE

BECAUSE IT WAS ATTENDED
BY THE PRINCE OF WALES.

THE PRINCE OF WALES

PRESUMABLY IS ONE OF THESE CHAPS
IN THE FRONT ROW.

THE REASON THIS LECTURE
IS WORTH REMEMBERING TODAY

IS NOT BECAUSE IT WAS ATTENDED
BY THE PRINCE OF WALES.

IT'S BECAUSE THE LECTURER
WAS MICHAEL FARADAY.

IN FACT, IT WAS AT A LECTURE
JUST LIKE THIS ONE,

NEARLY 200 YEARS AGO,

THAT THE YOUNG MICHAEL FARADAY
BECAUSE SO ENTRANCED WITH SCIENCE

THAT HE DECIDED TO GIVE UP
HIS PROMISING CAREER

AS AN APPRENTICE BOOKBINDER

BUT IN THAT SERIES
OF LECTURES,

THERE IS ONE MAN
WHO MADE A LASTING IMPRESSION
ON THE ENTIRE TRADITION.

HIS NAME
WAS CHARLESWHEATSTONE,

AND HE WAS A KEY FIGURE

IN WORKING OUT
THE NUTS AND BOLTS

That MADE
ELECTRICITY PRACTICAL.

THOSE NUTS AND BOLTS
ARE OUR SUBJECT FOR TODAY.

THE NUTS AND BOLTS
THAT HOLD TOGETHER

THE COMPLEX MACHINERY
OF THE MODERN WORLD

ARE NO MORE IMPORTANT
IN THE HISTORY OF CIVILIZATION

THAN THE SIMPLE
FLOW OF WATER.

LEADING TO CONTROL
AND HERNESS THE FLOW OF WATER

HAS BEEN
A CRITICAL INGREDIENT

IN THE DEVELOPMENT
OF CIVILIZATION.

IT WAS NO ACCIDENT
THAT THE EARLIEST CIVILIZATIONS

DEVELOPED ALONG THE BANKS
OF THE GREAT RIVERS,

THE NILE,THE TIGER,
AND EUPHRATES,

THE GREAT WATER CIRCUITS
OF NATURE
IN ORDER TO FLOURISH,

EVERY SOCIETY HAD TO DEVELOP
THE MEANS TO MANIPULATE,

CONTROL,AND DISTRIBUTE
THE FLOW OF WATER

FOR IRRIGATION,

FOR THE DRAINING OF SWAMPS,

AND TO NOURISH
THE GROWTH OF CITIES.

JUST AS ALL ROADS
LED TO ROME,

SO DID AN INGENIOUS NETWORK
OF AQUEDUCTS.

THE EMPIRE SURVIVED
AS LONG AS IT DID,

TO A LARGE DEGREE,

BECAUSE THE AQUEDUCTS
BROUGHT DOWN FRESH WATER

FROM THE HILLS OF ALBANUS

IN THEIR TIME,

THOSE COMPLEX CIRCUITS OF PIPES
THAT DISTRIBUTED WATER

TO THE CITY'S BATHS,
BUILDINGS,AND FOUNTAINS

WERE AMAZINGLY SOPHISTICATED.

BUT ONLY
IN THE LAST CENTURY

DID ANOTHER FLOWING TECHNOLOGY
BEGIN TO DEVELOP--

ELECTRICITY.

INVENTORS
SUCH AS THOMAS EDISON

FOUND WAYS
TO MANIPULATE ELECTRIC CURRENTS


TO LIGHT LAMPS IN HOUSES

AND TO CARRY DOTS AND DASHES
LONG DISTANCE THROUGH WIRES.

THEY ALSO CREATED WAYS

TO GENERATE
AND DISTRIBUTE ELECTRICITY

IN EVER MORE COMPLEX GRIDS.

BUT IN THE DAYS SINCE
EDISON'S ILLUMINATING STATION

WAS THE WORLD'S
PREMIER POWER PLANT,

ENGINEERS HAVE DEVELOPED
MUCH MORE SUBTLE WAYS

TO USE THE FLOW
OF ELECTRICITY.

TODAY,
A SINGLE COMPUTER CHIP

CONTAINS AN ELECTRIC CIRCUIT

AS COMPLEX AS THE STREET MAP
OF AN ENTIRE CITY.

AND IN PRINCIPLE,

THE VERY EXISTENCE
OF A MAJOR CITY

SUCH AS LOS ANGELES

DEPENDS ON MANY
OF THESE CIRCUITS.

L.A. IS,OF COURSE,
MORE THAN A FREEWAY.

BUT WITHOUT
AN ENGINEERING MIRACLE,

IT WORLD BE NO MORE
THAN A DUSTY VILLAGE

BETWEEN THE DESERT
AND THE SEA.

AND THAT MIRACLE IS CALLED
THE METROPOLITAN WATER DISTRICT.

WHETHER DESIGNING WATER CIRCUITS
OR ELECTRIC CIRCUITS,

IT ALL BOILS DOWN TO CONTROLLING
THE FLOW OF CURRENTS,

163,000 CUBIC METERS
OF WATER PER HOUR

FLOW THROUGH
THE COLORADO RIVER AQUEDUCT

TOWARD
THE LOS ANGELES BASIN.

1.3 AMPS OF ELECTRIC CURRENT
FLOW THROUGH THIS COPPER WIRE.

JUST AS WATER
MAKES LIFE POSSIBLE,

THE FLOW OF ELECTRICITY
MAKES LIGHT POSSIBLE.

HOW MUCH LIGHT

DEPENDS
ON THE AMOUNT OF CURRENT,

WHICH IS MEASURED IN AMPS.

1 AMP is 1 COULOMB
OF ELECTRIC CHARGE PER SECOND

FLOWING THROUGH A CIRCUIT.

IN OTHER WORDS,

ELECTRIC CURRENT,‡T,

IS THE RATE OF FLOW
OF ELECTRIC CHARGE,

AT ANY INSTANT,

THIS CURRENT IS THE SAME
EVERYTHING ALONG THE WIRE

BECAUSE ELECTRIC CHARGE ,
LIKE WATER,

IS NEITHER CREATED
NOR DESSTROYED ALONG THE WAY.

IT JUST
KEEPS FLOWING ALONG.

WHILE RIVERS HAVE FLOWED
FOR THOUSANDS OF YEARS,

ELECTRICITY WAS BASICALLY
A STATIC FIELD UNTIL 1800.

THAT WAS THE YEAR
ALESSANDRO VOLTA CHARGED AHEAD

AND INVENTED THE BATTERY

THIS NEW SOURCE OF POWER,
CALLED THE VOLTAIC PILE,

MADE A SUSTAINED FLOW
OF ELECTRICITY POSSIBLE

AND OPENED
THE FLOODGATES OF PROGRESS.

WITH IT,
SIR HUMPHREY DAVY

SOON EXTRACTED
BRILLIANT NEW METALS--

SODIUM AND POTASSIUM--

FROM THE COMMON SALTS
SODA AND POTASH.


A FEW YEARS LATER,

HANS CHRISTIAN OERSTED
DEFLECTED A MAGNETIC NEEDLE

WITH NOTHING BUT THE CURRENT
FROM A VOLTAIC PILE,

AND SO DISCOVERED
ELECTROMAGNETISM.

LATER, IN THE 19TH CENTURY,

THOMAS EDISON USED
THE CONTINUOUS FLOW

OF ELECTRIC CURRENT
PROVIDED BY A VOLTAIC PILE

TO DEVELOP
THE FIRST ELECTRIC LAMP.

HE ALSO USED THAT CURRENT

TO PERFECT A DEVICE
INVENTED BY OTHERS--

THE TELEGRAPH.

MUCH EARLIER,
KARL FRIEDRICH GAUSS

HAD SEEN THE POTENTIAL

IN OERSTED'S
TWISTED COMPASS NEEDLE.

AN ELECTRIC SWITCH
CLOSED IN ONE PLACE

COULD CAUSE A MAGNET
TO MOVE IN ANOTHER PLACE.

OTHERS SOON CAME 
TO THE SAME REALIZATION.

THE TELEGRAOH
HELD THE PROMISE

OF ALMOST INSTANTANEOUS
LONG-DISTANCE COMMUNICATION.

BUT IN THE BEGINNING

THE PROMISE OF
LONG-DISTANCE CALLING

WAS SHORT-LIVED

AFTER TRAVELING
A FEW KILOMETERS,

THE SIGNAL WAS TOO WEAK TO
ACTIVATE THE MAGNETIC DEVICE.

THAT PROBLEM WAS SOLVED
BY CHARLES WHEATSTONE,

A MUSICAL INSTRUMENTMAKER
AND A STUDENT OF ACOUSTICS.

HE FOUND THE SOLUTION
TO THIS DILEMMA

IN THE ALMOST
UNINTELLIGIBLE WRITINGS

OF AN OBSCURE
GERMAN PROFESSOR

NAMED GEORG SIMON OHM.

WHAT OHN HAD PREDICTED

WITH ABSTRACT
MATHEMATICAL REASONING,

WHEATSONE SHOWED
THROUGH DIRECT EXPERIMENT.

THE SIGNAL CAN BE
KEPT THE SAME SIZE

IF THE VOLTAGE IS INCREASED
IN PROPORTION TO THE DISTANCE.


WHEATSTONE HAD VERIFIED THE RULE
KNOWN AS OHM'S LAW.

TO MAKE A CURENTFLOW
THROUGH A CONDUCTING MATERIAL,

A VOLTAGE IS NEEDED,

THE CURRENT IS ALWAYS
PROPORTIONAL TO THE VOLTAGE.

THE CLNSTANT OF PROPORTIONALITY

IS CALLED THE RESISTANCE.

THIS EQUATION

IS KNOWN AS OHM'S LAW.

AN ELEMENT IN AN ELECTRIC

CURCUIT WITH RESISTANCE

IS CALLED A RESISTOR.

OHM'S LAW ISN'T
A FUNDAMENTAL LAW OF NATURE

LIKE NEWTON'S SECOND LAW

OR THE LAW OF
CONSERVATION OF ENERGY.

IT DOESN'T HOLD
IN ALL SITUATIONS,

BUT IT'S A USEFUL RULE
IN MOST PRACTICAL SITUATIONS.

IT HELPED TURN THE TELEGRAPH

INTO A VERY PRACTICAL
INVENTION INDEED.

WITH EDISON'S REFINEMENTS

AND THE CODE
DEVISED BY SAMUEL MORSE,

THE TELEGRAPH PUSHED BACK
THE AMERICAN FRONTIER

AND TOOK THE TRAIN WITH IT.

TELEGRAPH WIRES
PARALLELED THE TRACKS,

AND THE INFORMATION THEY CARRIED
WAS ESSENTIAL

TO THE SMOOTH RUNNING OF
THE ENTIRE RAILROAD SYSTEM.

NOT THAT
THERE WASN'T RESISTANCE

TO THE USE OF
BOTH OF THESE INVENTIONS.

PEOPLE SAID ELECTRICITY
WAS DANGEROUS,

AND SOME SAID THAT

AT THE FAST SPEEDS
TRAINS COULD TRAVEL,

HUNANS WOLDN'T
BE ABLE TO BREATHE.

BUT THERE WAS
NO STOPPING PROGRESS.

AND IN THE LONG RUN,
WIRES AND RAILS TOGETHER

PLAYED THE SAME VITAL ROLE
RIVERS HAD LONG PLAYED--

TRANSPORTERS OF PEOPLE,
CARGO,AND IDEAS.

AND THROUGH
MILES AND MILES OF WIRE,

THE FLOW OF INFORMATION FOLLOWS

FROM THE PRACTICAL USE
OF OHM'S LAW.

IN MUCH THE SAME WAY,

SIMILAR RULES
LEAD HYDRAULIC ENGINEERS

IN THE DESIGN
AND OPERATION OF AQUEDUCTS.

THOSE ENGINEERS HAVE
LONG KNOWN THAT THE RATE

AT WHICH WATER FLOWS
THROUGH A PIPE

DEPENDS ON JUST
A HANDFUL OF FACTORS--

THE SLOPE OF THE LAND
AND THE PRESSURE APPLIED,

THE LENGTH AND DIAMETER
OF THE PIPE,

AND THE VISCOSITY
AND DENSITY OF WATER.

IN PRECISE ANALOGY,

THE AMOUNT OF ELECTRIC CURRENT

THAT FLOWS THROUGH A RESISTORdepends on the voltage drop

across it

how wide and how long it is,

and what it's made of.

the resistance of 
an electric resistor

is proportional
to its area...

and proportional
to its resistivity,

or its tendency to inhibit
the flow of electrons.

this tendency to resist

is something
all materials have,

but to varying degrees.

adding resistors to a circuit,
one after another,

has the same effect 
as making one resistor longer.

these are called
resistors in series.

putting resistors side-by-side
increases the area

through which
the current can flow.

these are called
resistors in parallel.

they have a lower resistance 
than either one alone.

the same is true of water.

adding section of pipe
in a series

is the same 
as making it longer,

and so the resistance
to movement increaces.

but if the pipes
are added side-by-side,

they can carry more more water
more easily.

and these particular pypes
carry a lot of water,

lifting it up 1,600 feet
from the CORORADO river

to a point where it can 
from down to LOS ANGELES.

however, because the dom
and pumping station 

were designed to carry away
so much water,

the project itself encountered
some stiff resistance,

especially from ARIZONA,

the state which happens to be
on the other side of the river.

on the day construction began 
in 1934,

the ARIZONA STATE MILITIA
perched on the rim of the river 
with rifles and machine guns.

in this case,

the basis for resistance
was clear

the flow of progress 
for California 

was at the expense
of Arisona's future.

but what about 
the natural resistance

to the progress 
of electrons?

just what is the nature 
of electrical resistance?

under the influence
of an electric fild,

erectrons move
through a metal

much as a marble falls
through a viscous fluid.

if it weren't for resistance,
they would accelerate freely,

like a falling body 
in a vacuum.

but, as it is,
they move, on the average,

at a constant speed.

resistivity is like viscosity

the more of it 
a material has,

the slower a particle
will move through it.

but what srows 
the erectrons down?

in other words,
in a conductor,

what resists 
the flow of electricity?

inside a metal,

erectrons constantly move
in all directions.

here, just a few of them
are represented as dots.

they orbit through the metal

as if it were 
one giant molecure.

this kind of frow
encounters no resistance,

nor does it create

a net flow in one end 
and out the other.

under these conditions,

the conductor is in 
electrostatic equilibrium.

there's no erectric field
inside,

no voltage difference
from one end to the other.

but if a battery makes 
an electric current frow,

equilibrium is destroyed,

and an electric field is 
created inside the conductor.

inside a perfect 
crystalline metal,

if a sample of it 
could be found,

the mobile electrons
would continuously accelerate

like a penny 
falling in avacuum.

but in the real world,
crystals aren't perfect.

they have defects
and impurities,

and their atioms vibrate
with thermal energy.

electrons, accelerated by
the forceof the electric field,

bounce off each imperfection,

behaving somewhat like a ball
in a pinball machine.

all that bouncing,

all that stopping 
and restarting,

prouduces the resistance

that prevents the electron flow 
from building up speed,

so the elections move 
at a constant average speed,

creating a constant current,

under the influence

of a constant force.

as the electrons bounce off
the imperfections,

they set the atoms 
into larger vibrations.

so the electrical energy
of accelerated electons 



turns into the heat energy
of vibrating atoms.

and about 100 years ago,

a brilliant idea 
rose from that heat.

if a resistor gets hot enough,
it will glow,

and thomas edison found 
just the right materials

that would glow brightly.

of couase,
all circuits don't glow,

but they all produce heat,
whether it's wanted or not.

in computers, for instance,

fans are used
to eliminate unwanted heat.

in fact, some supercomputers
generate so much heat

that they require
a liquid cooling system

to keep the temperature down.

whether heat is the goal
or an unwanted by-product,

it takes power to produce it.

as current flows 

through a resistor,

the energy turned into heat

is equal to the amount 

of charge that flows 

times the change in potential.

the rate of heating,

or power consumed,

is equal to

the current times the voltage.

using ohm's law,

the power can also be written

as i squared r,

or v squared/r.

and what's the result?

well, to start with, 
it's measured in watts.

1 watt is a measure of power 
equal to 1 amp times 1 volt.

multiply that watt by 1,000
to get kilowatts.

multiply that 
by 1,000 again

to get megawatts.

at peak hours,

parker dam generates 
120 megawattes.

watts and water.

the electric grid 
and the water system 

it's a powerful analogy 
that takes concrete shape 

here in this hydroelectric 
generating plant.

if progress 
rides the currents 

of water and electricity,

it also demands 
a lot of each.

in america's 
enerrgy-hungry society,

each person consumes about 
a kilowatt of electric power 

all the time, day in 
and day out, all year long.

and each family consumes
about an acre-foot of water

that is, all the water 
in one acreof land

covered to a depth of one foot,
every year.

to deliver both water
and power to the consumers,

engineers must first master 

the art science
of circuit design.

the common elements of 
elementary wlwctric circuits

are wires and switches, 

batteries, resistors,
and capacitors.

and while these elements
can be combined

into networks of 
ever increasing complexity,

they always obey
the same simple rules

called kirchhoff's laws.

gustav kirchhoff,
a german physicist,

was keen on mathematics.

by applying ohm's law

and generalizing it fully,

he derived two laws,

and each expresses 
a familiar idea.

one of those ideas
is conservation of charge.

and the corresponding law
for circuits is

whenever one current sprits
into two, or vice versa,

the total current 
into the junction

will equal the total cerrent 
out of it.

kirchhoff's other law

expresses conservation
of energy.

an electric charge going
around any complete circuit

neither gains
nor loses energy.

consider an electric charge 
in space

not confined to a circuit.

if  it's moved through space 
on a path

that brings it back 
to its starting point,

no net work is done.

the electric potential,
or voltage,

may go up or down,

but it always gets back
to where it started.

the same is true 
inside a circuit.

notice that an intengral 
along a closed path

has a special notation

an integral sigh 
with a circle on it.

so, in the secial case

of an electric circuit,

all the voltage rises

due to batteries 
and charged capacitors

and all the voltage drops

due to currents 
flowing through resistors

add up to zero.

using these two laws alonne,

engineers analyze
the mostcomplex circuits.

to take just 
a simple example,

consider a capacitor

connected to a resistor 
and a battery.

even as the capacitor charges,

the total rise in voltage

equals the total fall
around the circuit.

a capacitor in an electric
circuit stores charge,

much the same way

a reservoir stores water 
for later use.

it takes time
tofill or empty either one.

how much time?

that depends, of course,
on how big the reservoir is

and how much resistance

these is to 
the water flowing out.

the bigger the reservoir 
and the more the resistance,

the longer it will take.

the same is true of charge 
draining from a capacitor.

applying kirchhoff's laws,
the time is found to be equal

to the capacitance
times the resistance.

of course, these are
no immediate plans

to drain lake havasu.

as fast as water is drained

to quench the thirst
of LOS ANGELES,

snow from distant mountains
melts to feed the COLORAD,

which in turn
refills the reservoir

as part of a global cycle
that conserves moisture

much as elestric circuits
conserves charge.

and so to the notion
of progress

is added the principle
of conservation,

perhaps proving that 
the more things charge,

the more they stay the same.

civilization still depends
on currents,

though the flow of electricity
has been added.

and the modern city,
as much as ancient rome,

depends upon and is limited by

the ability to channel
and distribute those currents.

today we've studied the rules
that make electricity practical.

they were first worked out

by people named
ohm and kirchhoff

and charles wheatstone.

wheatstone himself was
revered by his colleagues

in his own time,

but he was unknown
to the public.

he was a shy man

and morbidly timed 
in front of an audience

just like me.

in fact, that was the cause,
the way,

in which 
he managed to change

the tradition of public lectures
at the royal institution.

apparently,
one evening in 1846,

it was charles wheatstone

who was to give 
that evening's public lecture.

but at the very last second,

with the audience
already in their seats,

wheatstone panicked and fled,

leaving nobody
to give the lecture.

well, michael faraday
stepped in 

and gave a brilliant 
impromptu lecture,

speculating that light 
might be

some kind of a disturbance
of electricity and magnetism,

an idea proved right 
many years later.

that tradition
of public lectures

at the royal institution 
continues to this very day.

every friday evening
at 8:00 on the dot,

a celebrated scientist,

dressed just like this,
in formal attire,

steps out before
a glittering audience 

to deliver a lecture

on the latest developments
in science.

but for a half hour 
before the lecture,

that scientist has been 
kept locked in a little room 

to make sure 
he doesn't "do a wheatstone"

at the very last minute.

that's why i was kept
locked in that room 

until the beginning
of this lecture.

captioning is made possible by 
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captioning performed by
the national captioning
institute, inc.

captions copyright 1987
CLIFORNIA institute 
of technology,

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

public permormance of captions
prohibited without permission of 
national captioning institute

funding for this program
was provided by 

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