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[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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