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a while ago,


i showed you one way
to generate electric power


using a lemon


when you do that,



you get what's called
direct current


last time i showed you
another possibility


that involved using
a simple coil of wire


and a magnet.


when you generate
power this way,


the current runs
back and forth


and it's called
alternating current


this is the way


nearly all electrical power
is generated


the best way of doing it


is not to move the coil
back and forth


but to make it
spin around steadily


in the magnetic field.


that is the way


virtually all electrical power
is generated


generating power that way
requires energy


to spin the coil
against the magnetic forces


and drive
the corrent around.


that's usually done
using a heat engine,

a gas turbine which
is fired by a fossil fuel


like oil, coal, or gas,


or by a nuclear reactor,


or even by water
in a hydroelectric generator.


i wanted to show you
how to build one of these


in case you're ever
stranded on an island


and have to reconstruct
civilization from scratch


this is a water wheel
which goes around like that
when there's water
running on it.


when it goes around,
it turns a coil


between the poles
of this permanent magnet.


the electrical output
of the generator


comes out
on that oscilloscore,


which is a device
for showing the voltage.


as long as the trace
on the oscilloscope


is going across horizontally,
nothing is happening.


when we start generating
electric power,


it will start
going up and down.


all i have to do
to generate electricity


is to turn on the water.


get out your umbrellas
in the first few rows.


and there it is,


hydroelectric power.


hydroelectric power.


no mortal created it,


but 100 years ago,


one man could foresee
its enormous potential


as a child,
he'd read of niagara falls


and dreamt of a wheel
run by these cascading waters.


eventually, his dream
took the shape


of a vast
electric power grid


and spun like a dynamo


to drive the modern
industrial age.


the man's name
was nikola tesla,


and his vision,
a theory and practice


that could finally
harness the power of niagara,


was grounded in the principle
of alternating current.


alternating current, ac,


is an oscillating current.


it is produced by a voltage
that rises and falls,


positive and negative,
like a sine wave.


but as nikola tesla discovered,
defining alternating current


was just the beginning
of his ups and downs.


he wanted ac to power
everything on earth,


but in the real world,
the world of business,


that idea met 
with enormous resistance.


right from the start,
he came up against


the electrical powers
that were--


thomas alva edison,
that is,


and the advocates
of direct current.


direct current, dc,


is a steady flow
of electricity.


ideally, its voltage
is constant


and equal to the current,


which is also constant,


multiplied by
the effective resistance


of the current.


obviously,
on the basic issue


of alternating
versus direct current,


edison and tesla were
on different wavelengths,


and in what was called
the war of the current,


battle lines were drawn.


but the battle
reached far beyond


the comparatively safe domain
of scientific theory.


many other interests
were involved.


fortunes were made and lost,


powerful men and retreated.


just what was behind
all this sound and fury?


tesla arrived in new york
in 1894,


a 29-year-old immigrant
from eastern europe.


tesla had
a book of poetry,


fluency in a dozen languages,


and less than a nickel
in his pocket.


but he also had
a letter of introduction


to thomas edison,


who gave the young man a job
redesigning dynamos


at the edison machine works.


of course, there
was one condition--


the dynamos had to be
direct current.


and, of course,
since tesla was determined


to make alternating current
the world standard,


his career with thomas edison
had only one way to go.


within a year,
tesla had quit,


partly because edison allegedly
wouldn't keep his promise


of a bonus.


tesla soon fell
on hard times


and was, once again,
virtually penniless.


by sticking to his principle
of alternating current,


tesla had not only
hit bottom,


he'd thrown a wrench into
the most powerful machinery


on the face of the earth.


when it came to putting
electricity to work,


no man in the world


could hold a candle
to thomas alva edison.


he was seen as the mastermind
of the electric age.


as the electric general





of what became
the general electric company,


edison wasn't
called napoleon


somply because the actress
sarah bernhardt


said he looked the part.


even today his headquarters,


the edison laboratory
in menlo park, new jersey,


remains alive
in the public imagination.


as a fitting tribute,


it's been reassembled
from the ground up,


plank by plank,


and preserved
at the henry ford museum


at greenfield village
in dearborn, michigan.


when edison was alive,


he was the creative force behind
just about every bright idea


under the sun.


though edison's
own hearing was impaired,


his genius produced
the world's first phonograph.


and for the record,


he also invented
the motion picture camera.


it was in menlo park,
not hollywood,


that the movies
really began to flicker.


with this invention,
edison's ticker-tipe machine,


the blood pressure of business
could rise and fall


with the pulse
of the stock exchange.


and whatever the news,
it traveled far and fast


with edison's
vastly improved version


of the repeating telegraph.


in fact, he often
refined other's inventions,


making them more practical
and commercially viable


in the process.


others invented
the first telephone


and the first typewriter,


but edison developed both


into handy,
effective instruments.


on the other hand,


sometimes edison
sought to destroy,


not improve,


someone else's idea.


the glow
in thomas edison's heart,


unlike the one he'd
put here in menlo park,


was faint indeed
toward nikola tesla


and his idea
of alternating current,


and no wonder.


beginning with
the sally jordan boarding house,


the first home in the world
to be lit electrically,


edison's direct current
was on its way


to lighting every house
within the limited reach


of his network
of power stations.


and edison knew that even
in the simplest circuits,


tesla's alternating current
could be full of surprises.


for example,


consider a simple circuit


that consists of an alternating
voltage source,


a capacitor,


and an inductor.


according to the mathematical
rules of gustav kirchoff,


the rise in voltage
at the source,


never bigger than e sub o,


is equal to teh sum


of the voltage drops


around the circuit.


the result
is a differential equation


that can be written
in terms of the charge


on the capacitor.


the same differentical equation


also descrises
the displacement


of a harmonic oscillator


driven by
an oscillating force.


even a small force,


never bigger than f sub o,


at just the right frequency


causes oscillations
that grow bigger and bugger.


and that adds up
to the phenomenon of resonance,


which means that
in an ac circuit,


even a tiny oscillating voltage
can cause the flow


of an amazing amount
of electric charge.


sha da boo dee da doe


dee dee doe do do do


doe do dee dee do bop


of course,
in a mechanical system...


do weeeee!


the results of resonance
can be shattering.


but sometimes, it takes
electric resonance


to get the tune just right.


tesla was, in fact,


the first to describe
a network


of tuned resonant circuits
and raised antennas,


which is exactly
how radio and television signals


are transmitted
and received.


a single television station


is picked out
of all others








  because an ac circuit
is tuned precisely in resonance 

with the broadcasting frequency

that's true of radio 
as well as television 

electrical resonance occurs 

because,mathematically,
capacitors and inductors 

act a lot like
spings and masses

for example,

when a capacitor
starts to charge,

itcreates a voltage that opposes the sharge

in other words,

a capacitor opposes change 

in positive or negative charge

just as a spring opposes
expansion or compression

on the other hand,

when a voltage 
is applied to an inductor,

it takes a while
to get the current moving

or takes a while 
tostop it again 

so an inductor opposes
change in current

in the same way
the inertial mass on a spring

opposes change in velocity

but no natter
how precise the analogy,

differences can arise

for example,

when resonance occurs
in electrical oscillators,

it seldom lets people down,

but when resonance occurs
in mechanical oscillators...

things can get
out of hand 

in electric circuits,

resistance can help keep things
from getting out of hand.

for exmaple,

consider a capacitor
and a resistor

in an ac circuit

if the frequency is low enough,

the charging and discharging
of the capacitor

can keep up with
the oscillating applied voltage

but at higher frequency,
 
the capacitor can't charge
and discharge fast enough,

so no voltage difference
develops across it,

and nearely all the voltage 
is across the resistor

on the other hand, 

if an inductor's
in the circuit,

an low frequency
there's plenty of time

to build up current in it
without much voltage across it.

but at higher frequency,

the current in the inductor
can't change fast enough

before it has to turn around,

so the voltage 
in mostly across the inductor,

and there's not much left
across the resistor.

when all the elements

are in the same circuit
at low frequency,

most of the voltage
goes into charging
the 
and discharging
the capacitor.

at higher frequency,
more of the voltage

is used up trying 
to change the current

in the inductor.

in fact,
at very high frequency,

the inductor virtually
keeps any current

from flowing at all

but if the frequency
is just right,

in other words,

at the resonant
frequency,

a quite large current flows.

the capacitor charces
and discharges,

current builds up and reverses
in the inductor,

and the resistor eurns up
enough energy

to keep the oscillations
under control.

of course, 
edison and company

still had the business
of electricity under control,

and to retain that control,

they put up
plenty of resistance

against the increasing powers
of alternating current.

so,if tesla was to win
the war of the currents,

he'd need a champion
to rise up and do business

against the forces
of thomas edison.

that's where george westinghouse
came into the picture.

westinghouse,the legendary
industrialist of pittsburgh,

was an inventor
turned big businessman.

but in contrast to edison,

he not onry spoke glowingly
of alternating current,

he put his money
where his mouth was 

and bought tesla's patents
for a polyphase induction motor.

and in 1888,

the war of the currents
escalated.

as westinghouse went to work
in support of tesla,

edison'swell-oiled machinery
shifted into high gear.

there were smear campaigns

there were smear campaigns

and,according 
to some people,

dirty tricks.

occasionally,however,

there was a meeting 
of the minds.

charles steinmetz,

the mathematical wizard
of physics and engineering,

offered a certain
intellectual support

to both camps.

edison and tesla were
even able to work together,

but not for long,

and never as long as tesla

had the advantage
of alternating current.

in theory 
and practice alike,

why was tesla's method better?

obviously,the reason a plant
generates electricty

is to send power somewhere,

to transmit it
through power cables

into the home,the office,

or anywhere else
there's a need

and a handy socket.

but the power is equal
to the current

times the voltage.

therefore, the same power
can be transmitte


at high current
and low voltage,

or low current
and high voltage,

which is better?

remember,

the power cables have,
a certain amount of resistance,

and the longer the distance,
the bigger the resistance,

because a cable's resistanace
is proportional to its length.

and,of course,

passing current
through a resistance

causes heating,

which is equal
to current-squared

times resistance.

this is wasted heat,

for the power company
and the consumer,

that means a certain amount
of energy won't be available

at the other end.

since I is P/V,

that heating is 
P-squared R/V-squared.

so for any given power
and resistance,

the higher the voltage,

the less power losy
in transit

in other words,

the key to transmitting power
efficiently

is to transmit it
at the highest possible voltage.

in a modern electric power grid,

energy is routinely transmitted
over thousands of kilometers

at hudreds of thousands of volts.

but no matter
how it's used,

the recipient wants
all those watts

toarrive at a safe
and handy voltage.

and that's possible only
if the electric energy

can be transformed
up to high voltage--

which it takes

to make the long trip
to the consumer--

and back down
to low voltage

for use at the end
of the line

that task, raising
and lowering voltage,

is hard to accomplish
with direct current,

but with  ac
it's comparatively easy.

if alternating current
passes through a loop,

or coil

it produces a constantly
changing magenetic flux.

a bar of iron,
magnetized by the coil,

can concentrate and intensify
the changing flux.

in fact, an iron ring
can contain the flux entirely.

and if a secondary circuit
is wound around the ring

as the changing flux
passes through it,

a voltage
is induced in it.

that voltage
is proportional

to the number of turns
around the iron.

obviously, then,
the voltage of the power

transmitted
to the secondary circuit

can be made higher
or lower

than the voltage 
in the primary circuit.

so although the power out 

is nearly equql
to the power in,

it can be stepped up
to high voltage

for long-range transmission

and then brought transmission

and then brought down
to low voltage

for long-range transmission

and then brought down
to low voltage

for safe use 
at the end of the line.

it's exactly this principal
which is the greatest advantage

of tesla's ac
over edision's dc.

and which it was revolutionary
at the end of the 19th century,

that principle
would be applied

from one end of the earth
to the other in the 20th.

that fact--
the overwhelming evidence

that alternating current powers
the modern industrial world--

makes the case
for declaring tesle the einner

in the war of the currents.

on the other hand, 
with wars and stories sides.

there aner always two sides.

considering edison's
enormous contribution

to the world of science
and engineering,

after all,

edison did have a convincing
number of patents.

before tesla,

edison built
his own generators,

one after another,

each more powerful
htan the last.

but then, so had tesla.

and surelysa wall 
as edison,

he, too, vuilt
turvines and motors.

however--and this
was the bid difference

in the long run--

edison's generators
could only illuminate things

within the reach
of his power plant,

while tesla's ac system

could reach beyond
the old neighborhood.

with an ever-expanding grid 
of power lines,

ac could go 
from coast to coast

and just about everywhere
in between.

nonetheless, thomas edison's
place in history was secure.

and in history was secure.

and in menlo park,
new jersey,

his mind was still as lively
as his motion pocure camera.

as an american inventor
and electrcian,

as an american inventor
and electrician,

no one since ben franklin

had gone as far
as thomas edison.

but in his own way,

nikola tesla
would go even farther.

long becane a realith,

tesla had envisioned 
vacuum tubes

coated with phosphor

and glass tubes
filled with gas--

fluorescent loghts
and neon lights.

and years before
the wright brothers appeared,

tesla claimed that if aviation
were to get off the ground,

it would need to use
a then almost unknown metal

called aluminum.

and thile guglielmo marconi

got the acclaim
of the popular press

for invention the radio,

nikola tesla got the vredit,
as well as the final verdict,

in the courts.

speaking of credit,

some state that tesla
was denied his due

for many original inventions.

in all,no one 
can denythat tesla

was one of the most dunamic
scinetists who ever lived,

nor that his mind
was fertile

and inventive
beyond compare.

but tesla, more interested
in invention

than in scintific publications,

kept much of his methodology
in his head.

perhaps that's why
the scientific community

remained dubious or miserly
with its praise for years.

he did, however,

receive honorary doctorates
from columbia and yale.

and in the end,
with unintended irony,

nikola tesla was even honored
with the edison medal,

that most prestigious award

named for none other
than thomas edison himself.

throughout this long yarn
we've been spinning,

there have always been
certain individuals
whom we could identify
as the saints of science.

these were people who were
driven to science.

these were people who were 
driven to scientific discovery

the way moths are attracted to light.

they would include
kepler and newton, faraday,

and certainly
albert einstein.

some of these people
did very well for themselves.

in fact, a few
became puite wealthy.

but was not money

that drove them to do
what they did.

but at the same time,

there's always been
a different kind of genius.

these were people
just as clever as the others,

but people who had their eyes 
fixed on the bottom line.

onem of course, 
was thomas edison.

there was also james watt 
and henry ford,

and there were
many others.

such prople typically spent
as much time in law courts

litigation patens

as they spent 
making their inventions.

one is tenpted
ti daraw a dustubctuib

betweeb tge saubtly scientists

and the money-gubbing
thchnologists.

but, of course,

there ws an exception 
that proved the rule.

I've never liked
that phrase--

the exception
that proves the rule.

I think it must come 
from an archaic meaning

of the word "to prove,"
which used to mean "to test."

an exception
tests a rule.

if it's truly an exception,
the rule isn'n right.

there was an exception
who tested the rule

and found ir wanting,

and that was nikola tesla.

tesla was certainly a genius]of the first magnitude.

if michael faraday
could imagine space

filled with lines
of fonstant force,

nikola tesla could picture 
multiphase generators

all multiphase motors

all commected with 
coplex electrical circuirs,

and when they were built,

all of it would]work perfectly,

exactly as he had imagined it.

time and again,

tesla made fortunes
and squandered them,

but turned down soft jobs
with fat salaries

just so he could
be left alone

to think and to invent.

you might say that tesla,
like da vinci before him,

was a true saint
of engineering.

he died, almost forgotten
and almost penniless,

in new york city.

but it was nikola tesla,

at least as much
as thomas edison,

who shaped the nature
of the world

that we live in today.

that we live in today.

ok.I'll see you next time.

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captions copyright 1986
california institute
of technology.

the corporation for community college televition, 
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the mechanical universe
is a college course

with textbooks published
by cambridge university press.

for more information
about the course,

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end of file