Before we're going to dive
into electromagnetic waves,
I would like to discuss a few more
mechanical resonances with you.
Last Friday, we discussed the resonances of
string instruments and wind instruments.
But there are several that you see around
you quite often, without realizing it, perhaps,
that you're looking at a resonance frequency.
You may have noticed that traffic signs
have the tendency, sometimes, to do this
and at certain wind speeds,
they go like this.
Enormously strong amplitude,
that's a form of resonance.
Undoubtedly, you have been motels or at homes
where you open a faucet
and then all of a sudden, when the water's running in a certain way,
you hear an incredible noise,
a terrible noise.
You close the faucet a little,
or you open it a little further,
and that noise goes away.
That's clearly an example of resonance.
You drive your car,
or you're in someone else's car
 and at a certain speed
something begins to rattle.
Very annoying.
You go a little faster, it stops.
You go a little slower, it stops.
Or, if you go a little faster,
something else begins to rattle 
there's some other resonance,
of something else in the car.
And of course, there are cars whereby
something rattles at any speed.
But in any case, there's always this idea, then,
of resonance, which is all around us.
I remember when I was in a student,
and when we had an after-dinner speaker
which we didn't like, we would all very quickly
empty our wine glasses
in those days, we were still allowed to drink,
by the way
and what we would do is the following,
something extremely annoying.
We would generate the fundamental
of our wine glasses.
You take your finger, you make it wet
and you rub it like this.
Listen.
[Rubs glass, creates tone]
Believe me, if hundred students do that,
it's very annoying.
But it's also extremely effective.
[laughter]
Speaker-- speaker gets the message
very quickly.
[Rubs glass again]
What the glass is doing, it's the fundamental
of the glass, it's the lowest frequency,
the glass is actually doing this.
And there are rumors that people can break
glasses by singing.
And we'll talk about that in a minute.
Um, I remember a, um, commercial,
Memorex.
Memorex is an audio tape.
And they bragged
about breaking glasses,
some of you may actually have seen
that commercial.
There was a, uh, a picture that I can show you
that goes with the commercial
and then a very dramatic story.
The story is that someone goes to a concert.
And there is a woman singer,
puts a glass on the table,
raises her voice,
hits the resonance frequency of the glass...
[pshew!]
...and there goes the glass.
And this gentleman was recording it,
of course on his Memorex tape.
So let's, um, see this, uh,
this slide.
So if we get the slide, yeah!
You see this, um, this glass, maybe you
can focus a little better John, thank you.
Memorex.
And so the story then goes that the guy
goes home and tells his wife about this.
Well, she is smart enough
not to believe this story.
But he plays back his tape.
And at the moment that this glass
breaks at the concert,
he has some wineglasses himself at home
and lo and behold, they also break.
And so then idea is, that is the commercial,
that's the great pitch of Memorex,
that the reason why they break at home is because of the enormous quality of this tape
which is made of very special material.
And the material, as you could have read
on the box,
is a very special chemical compound,
it is M R X two.
Two atoms of X, one of R and one of M
and then you make it oxide
and then you have the best tape
that you can imagine in the world.
Well, they overlook a small detail
and that is that, um, for one thing,
a tape recorder would never generate enough
volume to break a glass in the first place.
But in the second place,
the glasses that this guy had at home,
obviously didn't have exactly the same resonance
frequency as the glass at the concert.
So this could never had happened.
But like with all commercials,
you know that you're being swindled
and this, of course,
no exception.
I've always questioned whether it is actually
possible, that a person,
without the aid of strong amplification and without
the aid of huge sound volumes
which you can generate with loudspeakers, whether you can actually break a glass.
I've always wondered about that.
People say it can be done.
Caruso, famous singer, was known
for being able to do that.
He put the glass there,
he would rub it with his finger
so that he knew the resonance frequency...
[kllk]
...and there he would go, and...
[poit]
...bingo.
Frankly speaking, I don't believe it.
I don't believe it can be done by a human being
without the aid of amplifiers and speakers.
And when I lectured 801, several years ago,
together with Professor Feld here at MIT,
we discussed the--
the possibility of designing something
that actually would be able
to break a glass, and--
and he actually deserved a lot of credit for that,
he worked with a graduate student
and he managed to design a setup
that works most of the time.
But don't put your hopes too high,
it doesn't work all the time.
So here is a wineglass,
the same series as that one.
By the time when-- when he got it to work,
we bought five hundred of those glasses,
we got a good discount, by the way,
because we wanted to be sure
that we can do it
for years to come.
So here's the wine glass
and here is the loudspeaker
and we are going to generate sound very close
to the resonance frequency of this glass,
which we have already determined
before you came in,
four hundred and eighty eight Hertz.
You're going to see the glass there
and to make you see, actually,
this wonderful motion of the glass,
we will strobe it with light
at a frequency slightly different
from the frequency of the sound
so that you see the glass move
very slowly.
And then we will increase
the volume of the speaker
and then with some luck,
if we are right on resonance...
[poit]
...the glass may actually break.
I think this is the sound that you're going
to hear at low volume.
[tone]
And I think I turned on the, um,
the strobe light now.
[tone]
So I'm going to go make it dark.
[tone]
And I want to warn you that the sound level
is going to be quite high.
[tone]
I will have to protect my ears
[tone]
and you actually
may have to do the same.
[tone]
I will first increase the volume of the sound
to see whether I'm close enough to resonance.
[tone]
So this slow motion that you see
is the result of the strobe, 
which is not exactly at the same frequency
as the glass.
I can change that a little.
[tone, pitch changes slightly]
All right.
So we are very close to resonance.
The glass is clearly responding
to the sound
and now I will cover my ears
and slowly increase the sound volume.
[tone, volume increases]
[tone]
[tone, volume increases]
[tone]
I can't go any louder.
[tone]
It's tough glass.
[tone]
[glass breaking]
[tone, lower pitch due to slow-motion replay]
[glass breaking]
[tone]
It was a tough glass.
[applause]
I think you will probably agree
with me now that
 for a person to do that without electronic help
is just not so believable.
The most dramatic example
of destructive resonance
is the collapse of the bridge
in Tacoma in 1940.
Many of you may have seen that dramatic movie,
but some of you may not have seen it.
And even if you have seen it,
it's worth seeing it again.
With a little bit of wind,
there's a little bit more wind
and just like with these wind instruments,
you're dumping a whole spectrum
of frequencies onto a wind instrument
and it picks out the resonance frequency.
And this bridge, as you're going to see,
picks out its own resonance frequencies.
And the consequences are quite dramatic.
So if you can start, Marcos,
with this movie.
Movie: (dramatic) music playing
Dawn of a fatal day and the wind begins to speak with a roar that no man can fail to hear.
Music continues...
In a forty mile an hour gale the feathers pan weaves like a ribbon
in a swinging swift
that you wouldn't believe possible.
Unless you could see it as you do now.
Music continues...
There is an automobile caught on the heaving road way.
The eleven thousand ton feathers pan swifts and swings the giant cables that support it.
Cables of sixty three hunderd wire slams,
each seventeen inches thick.
Music continues...
No structure of steel and concrete
can stand such a strain.
Steel girders buckle and giant cables snap like [two leaf branch?]
There it goes!
Music continues...
Engineers are divided as to the cause
of the disaster.
Some claim it was the use of solid girders.
Others differ, but whatever the reasons,
Tacoma will rebuild.
This time a bridge that will not provide
a super thrill [swirl? swell?] in the news.
Music continues...
No other example of re-- destructive resonance
is more impressive than this one.
All right, so now,
we've had so much fun
and we have to really
get into electromagnetic waves.
So we turn back to Maxwell's equations
as you see them here.
And Maxwell, who was credited for this extra
term that he added to Ampere's Law,
the displacement current term,
was able to predict that electromagnetic waves should exist,
he predicted the existence of radio waves,
which were later discovered by Hertz
and that was a great victory
for the theory.
But, as I will show you today, there was another
enormous victory around the corner.
Electric and magnetic fields
can move through space
and satisfy all four
Maxwell's equations.
The electric field results
from a changing magnetic field
and a magnetic field results
from a changing electric field.
So one exists at the mercy of the other
and the other exists at the mercy of one.
Together, they propagate through space,
they can even propagate through vacuum,
where there are no charges
and where there are no currents.
Very mysterious.
I will write down a possible solution
of an electromagnetic wave
which meets all four Maxwell's equations
and this is the graphical display of those waves
that I'm going to write down.
But I will discuss that with you in a minute.
The electric field is only in the direction of x--
this is the magnitude,
the largest value of the electric field,
it's only in the direction of x.
Cosine k z minus omega t.
This is the frequency and the minus sign tells you that it is traveling in the plus z direction.
B, the associated magnetic field, is B zero,
only in the y direction,
with exactly the same
cosine minus omega t term.
So if I plot this at time t equals zero,
then you see this curve right here.
And you see the magnetic field curve here.
The magnetic field is only in the y direction
and the electric field is only in the x direction.
And this is a package that, together,
moves in the direction of plus z
with this speed,
which is omega divided by k.
And the wavelength from here to here
is then two pi divided by k.
We call them plane waves and the reason
why we call them plane waves is that,
 if you take a plane, anywhere perpendicular to z,
that no matter where you are in that plane,
at that moment in time, the E and the B vector
are everywhere in that plane the same.
So think of this as a plane perpendicular
to the z axis
and then this whole train passes by you.
And so you see the electric field vector like this,
becomes zero, like this, becomes zero, like this.
And the magnetic field vector, maximum,
zero, this direction and so on.
But that's why they're called
plane waves.
These equations only satisfy Maxwell's equations
under two conditions.
And one condition is that B zero is
E zero divided by C
and the other condition is
that omega divided by k,
which is the velocity, with which it propagates,
I will call that C, 
in vacuum, we call the velocity of electromagnetic
radiation C,
that is one divided by the square root
of epsilon zero, mu zero.
If that's the case, my two equations
will satisfy Maxwell's equations.
Imagine the victory for Maxwell.
Maxwell was not only able to predict
the existence of electromagnetic waves,
but he was even able to predict that they would
move through vacuum with that speed.
What an unbelievable victory,
when you come to think of it,
that epsilon zero can be measured,
in a static way,
it follows from Coulomb's law,
has nothing to do with the dB dt,
has nothing to do with the dE dt.
Has nothing to do with traveling waves.
Epsilon zero is about eight point eight five
times ten to the minus twelve in SI units.
Mu zero is equally static, can be measured
from the force at which two wires, 
through which you run a current,
attract each other.
No dB dt, no dE dt, there's nothing to do
with electromagnetic waves.
Mu zero is about one point two six times ten
to the minus six in SI units.
And if you multiply them
and substitute them in this equation,
you will find that C equals two point nine nine
times ten to the eight meters per second.
Unbelievable.
What a success for that theory.
It always baffles me how two quantities
so static
and seemingly so unrelated to moving waves,
with dB dts and dE dts all over the place,
how they can predict the speed of light.
Suppose I ask you to measure the pressure
in your tires of your car
and I would ask you to also measure
the voltage of your battery
and then to predict the speed of the car.
It's almost something like that.
It is bizarre.
But it works and it was a great victory
and of course, it justified entirely this one term,
which is this displacement current term.
Together, you and I will prove that this is,
indeed, a necessary condition
so that these equations
satisfy Maxwell's equations.
We will do it together.
I will do 50 percent and you will do the
other 50 percent at assignment number nine.
So we split this bill fifty-fifty.
I will make a new drawing and I will do something
that I rarely ever do in lectures,
 I will give you eight minutes of hardcore math.
You're going to hate it.
I'm going to make a new drawing, which is
not too different from what you have there.
So this is z, this is x and this is y.
And at t equals zero, I'm going to draw here
the electric field like so.
So this is E zero, electric field is this strength
and now I'm going to apply Ampere's Law,
that's my half of the bargain, closed-loop integral of B dot dl, you see there,
equals epsilon zero times mu zero
times d phi E dt.
We're dealing with vacuums, so kappa M is one,
and the dielectric constant is one.
And there is no such thing as a current I,
because we are in empty space,
so this whole term does not exist.
What does Ampere's Law require?
I need a closed loop
and I need a surface that I attach
an open surface to that closed loop.
I'm going to choose a closed loop
in the plane y z.
And this is going to be my closed loop.
This here is going to be my closed loop.
This length is l and the length, or the width,
of this side, is lambda divided by four.
I have to do a closed loop integral of B dot dl,
I will do that last.
I will first do the hardest part,
which is the time derivative of the electric flux
through this surface.
The problem is that the electric field
is not constant.
The electric field is zero here
and has a maximum here
and falls off in this way.
So I have to do an integral.
So I'm going to make a slice here
and this slice here has a width dz.
And in that very narrow slice,
the electric field is approximately constant.
Right here,
the electric field has this value.
But everywhere in that slice,
it has the same value,
because remember,
it's a plane wave.
And so I will draw here a line parallel
and so everywhere in that slice,
the electric field has exactly this value.
And that value is given by this equation.
If you tell me what z is at time t equals zero,
I know what that value is, that's this value.
So now I have to calculate
the electric flux.
So phi of E, I have to take the dot product
between dA and the electric field.
Remember, flux is the dot product,
E times dA.
I will choose dA up, because E is also up,
so that makes life easy,
I have to remember that later, then,
when I do the closed loop integral of B dot dL,
then looking from below,
I have to go clockwise, because I remember
the right-hand corkscrew rule.
So I get all my minus signs and plus signs
just right.
So dA and E are in the same direction.
So what is dA of this little slice?
That is l times dz.
So I get l times dz.
What is the local electric field in this slice?
Well, that's that equation.
So I get E zero times the cosine of k z
minus omega t.
This x roof, of course, is gone,
because the A and E are in the same direction,
 I have already taken that into account.
But I have to integrate this now,
from z equals zero to lambda over four, 
because I have to integrate it
over this whole surface.
So that's the--
the answer.
But I'm not interested in phi E.
I have to know d phi E dt.
So it's going to be worse for you.
I told you, eight minutes,
pain in the neck.
So I'm going to take the time derivative
of that function, so d phi E dt.
L and E zero can come out, that's no problem,
they are constants.
I take the time derivative of cosine k z
minus omega t, then minus omega pops out
and the cosine becomes a minus sign.
So I get minus the sine of k z
minus omega t.
And I have to do an integral, here is my dz,
zero to lambda over four.
This minus sign eats up this minus sign.
I have to do the integral, but I do that at
t equals zero.
In other words, this thing goes away,
because t equals zero.
So I'm getting close.
So I'm going to continue here, so I get l
times E zero, I have an omega
and now I have to do the integral of sine k z dz.
Well, the k z means I have to get a k out,
which is here
and then the integral of sine dz is simply
minus the cosine of k z
and I have to evaluate that between zero
and lambda over four.
If I evaluate cosine k z between zero
and lambda over four, that's minus one.
I'm sure you can do that alone.
Times this minus one makes it plus one.
And so the answer is l times E zero
times omega divided by k,
but we call that c,
in vacuum,
that is the speed of
electromagnetic radiation.
So this is the answer to d phi E dt.
Now, we have to do the closed loop integral
of B dot dl.
And that is easy.
At this moment in time, B is the maximum here,
which is B zero
and then it falls off to zero here.
You can see the same there.
Suppose I start here and I go this way,
this way, this way and this way.
Closed loop integral.
If I go from here to here, my B and dl
are at ninety degree angles.
B is coming to you, and Bl--
dl is like this.
So there is no contribution here.
If you go from here to here,
well, B is zero everywhere along the line.
So integral B dot dl
from here to here is zero.
It's a plane wave, remember?
B is zero here, it's also zero here,
it's also zero here, it's also zero here.
If you go from here to here, B and dl are,
again, at ninety-degree angles,
so there is no contribution,
so there's only a contribution
due to this portion.
And that is B zero times the length l.
And now you see why I chose the width
lambda over four,
so I get a very easy result.
So I find then, that B zero times l,
which is the left part of Ampere's Law,
well, it's too much to give Ampere credit,
all the credit,
because it's really Maxwell who added that term,
d phi E dt.
And so this, now, is epsilon zero mu zero,
which you see upstairs there,
 times the result that we have here.
Oh, by the way, this is E zero,
times l, times E zero, times c.
And I lose my l.
And you see here a result
that is quite remarkable,
even though it doesn't look so
remarkable to you, yet.
The reason is, that you are going to do
the other half.
You are going to apply Faraday's Law for me.
I only used Ampere's Law, you're going to--
in assignment nine, use this relationship,
which will allow you to prove this.
And once you have this, substitute for B zero,
E zero divided by c
and you see immediately
that the speed of light then, has to be this.
This is your task.
I did this end.
Yours is no easier than mine
and I advise you to also,
use this quarter-wavelength trick.
If you know the frequency
of the electromagnetic radiation
then the wavelength
follows immediately
and so you see here a few examples
that I've calculated for you.
If you start out with a low frequency
of thousand Hertz,
you get a wavelength
of three hundred kilometers,
radio waves, megaHertz,
still talk about radio waves,
but when you go up in frequency, the wavelengths, of course, get shorter and shorter,
we would call these radar waves,
microwaves.
If you go to ten to the fourteen,
ten to the fifteen Hertz,
you get into the domain of infrared
and visible light and the ultraviolet,
and if you go even higher,
then you end up with X-ray and ultimately,
gamma rays.
All of these are members of the electromagnetic
family, electromagnetic waves.
This A with a little zero there
stands for angstroms.
That means ten to the minus ten meters.
So, a whole family
of electromagnetic waves,
and we give them names
so we can talk about them
without ever mentioning the specific
frequency or the-- or the wavelength.
So given the fact that electromagnetic waves
then travel--
with three hundred thousand kilometers per
second, one foot would take one nanosecond.
Twenty six one hundred,
thirty meters deep.
The light, for me, to Professor Bertozzi
all the way at the end
would take about oh point one microseconds.
One second, light,
radio waves to the moon.
Eight minutes it takes the light
from the sun to reach us.
The light from the nearest stars
will take five years.
And the nearest large galaxy
to the Earth
would take two million years
for that light to reach us.
So when you look at that galaxy,
 then you see the galaxy the way it was
two million years ago.
In astronomy, we use as our meter stick,
a light-year,
which is the distance
that light travels in one year,
 which is about ten to the sixteen meters.
If you study a galaxy which is at a distance
of ten billion light-years,
you're looking at the universe the way it was
ten billion years ago.
So in astronomy, you can look back minutes,
you can look back years,
you can look back millions of years,
but you can also look back in time
billions of years.
Most forms of electromagnetic radiation,
certainly light and radio waves and radar--
can reflect off surfaces.
At least, to some degree,
it depends on the surface.
And this is the basis behind
the distance determination.
When you send a radar pulse to an airplane,
or to a rainstorm,
some of that radiation comes back at you
and you know the speed
and so that allowed you
to calculate the distance.
If the distance to the plane is d
and you send a brief pulse
and it comes back,
they call it the echo
and it takes a certain
amount of time to come back,
which you can measure,
then that signal has traveled
twice the distance,
so that is the speed of light times t,
this is what you measure,
the distance in time from the moment
you sent the signal
until you get the reflection back
and so you can calculate the distance.
The distance to the moon
can be measured this way.
There are five corner reflectors on the moon.
Three were left there by the Americans
and two were left by the Soviets,
 in the days that it was still the Soviet Union.
An optical telescope from Earth can send
a very brief pulse, laser pulse,
to these corner reflectors.
The l-- the time, the length in time of this pulse
is only one-quarter of a nanosecond.
Just imagine, light only travels seven centimeters
in one-quarter of a nanosecond.
So the kind of wave that you get
is really not very much of a plane wave,
 the way we envision it.
But in any case, this pulse goes to the moon,
and then some of it comes back,
it's reflected off these corner reflectors.
There are two times ten to the seventeen photons,
roughly, in one of these pulses
and only one comes back
per ten pulses.
So not much comes back.
But it's enough, if you integrate it to get
an accurate distance determination
between us and the corner reflectors,
the accuracy is about ten centimeters.
And the goal is really to get a handle
on the precise orbit of the moon.
I can show you these corner reflectors
the way they were built on Earth
and then I will also show an optical observatory
as it is sending out these quarter-nanosecond pulses, laser light, to the moon.
So this is, uh, one of those corner reflectors.
They are designed in such a way
that if light strikes it in a certain direction,
that it reflects the light in exactly the same direction backwards, hundred eighty degrees,
very clever design.
And so the next slide will show you, in Texas,
McDonald Observatory is sending, here,
these short, brief pulses,
laser light, to the moon
and what you see here is simply some scattered
light of the dust in the Earth atmosphere.
And then only a teeny weeny little bit of that
comes back,
but that is enough to get the distance
to the moon.
There are, on the moon, 
this is enough for this slide, John, 
there are, on the moon,
several cameras.
They were left there by Surveyor,
they are small cameras.
The lens, I think,
is only two inches across.
And they keep an eye on the Earth
all the time.
Something that you may never
have thought of,
that if you were on the moon
and you look at the Earth, 
and the Earth is there, say
that an hour from now,
the Earth will still be there.
And ten hours from now,
the Earth will still be there
and ten years from now,
the Earth will still be there.
As seen from the moon,
the Earth never moves.
Of course,
it rotates about its axis.
You will see that.
You will also see that certain parts of the
Earth are at night and others are at day,
that's different, but it's always
in the same direction.
So it's very easy for these cameras
to keep an eye on us, so to speak.
All you have to do is to aim them in one direction
and you never have to change that direction.
Imagine that you and I were now on the moon
and we were looking at the Earth.
And you, for instance, would see the Earth
as you see it here.
Here is North America
and this part of the Earth
happens to be daylight
and here it's night.
And this is the moment that these cameras
are going to take a picture of the Earth.
So you expect to see a lot of light here,
and you expect this to be night,
 here is New York.
You may think that there is so much light
coming from New York
that you may actually see New York,
that a picture taken by these cameras--
actually may show you New York.
Well, you won't, but you see something else
which is very dramatic,
that's why I show this to you,
because the picture you're going to see next,
John, you can show it, is at the time
that two observatories on Earth
were both sending these laser pulses
to the moon.
And here you see one in Arizona
and here you see one in California.
But you don't see New York.
Isn't that amazing?
That you're on the moon
and you know there's really life on Earth,
someone is blinking at you.
Well, you don't see the blinking,
but you see these lights.
Very dramatic shot.
Thanks, uh, John, that's fine.
Radio waves can be generated
by oscillating charges.
I will talk about that a great deal
the next lecture.
So you run alternating current through wires
called antennas, this is an antenna
and then you create electromagnetic waves.
And radio stations transmit
at a well-defined frequency.
For instance, WEEI transmits
at eight hundred and fifty kiloHertz,
wavelength three hundred and fifty three meters.
Eight hundred and fifty kiloHertz is an extremely
high frequency.
How come I can hear things, that I can hear music
and that I hear someone speak? 
Well, this signal, we call this the carrier wave,
is being modulated.
The strength of that signal is modulated with
the frequency of audible sound,
 we call that, therefore,
amplitude modulation.
So, for instance, if you looked at this signal
as a function of time,
then this would be the audio modulation
of that signal.
But the transmitter would transmit
eight hundred fifty kiloHertz,
here, the signal would be a little stronger,
here a little weaker, here a little stronger
and if this were a thousand Hertz tone,
then this would be one millisecond.
At the receiving end,
you tune your radio,
you change a capacitor
somewhere in your radio,
you have an LRC circuit, so that you are exactly
on resonance at eight hundred fifty kiloHertz,
and you're not on resonance
at eight hundred and forty kiloHertz,
so you don't hear other stations,
but you really tune in on that one station
and you can receive this signal, then.
And then you do some demodulation
to only hear the audio envelope
and you hear speech
and you hear music.
That's the idea.
Right here in twenty six one hundred,
we have a transmitter
and I can transmit sound at almost any frequency that we choose.
We have decided in honor of you,
to transmit a one kiloHertz audio signal
 at eight zero two kiloHertz.
The eight zero two is in honor of you.
At eight hundred and two kiloHertz,
there is no radio station,
so this is a nice thing to do.
We're not interfering with anyone.
We're going to transmit it here
and then we have a radio here,
and we are going to search for that signal
at eight hundred and two kiloHertz.
That's what we're going to do first
before we're going to do some other things
which are not so nice.
Now, Marcos is an expert,
in order to get the frequencies right,
so Marcos has promised to help me with this,
very nice.
[tone]
Oh, boy, you're already on, we are already transmitting at eight hundred and two kiloHertz
and the station is already receiving it,
the station meaning our radio.
[tone]
Marcos, let me convince the students that,
indeed,
[tone, pitch changes]
that it, oh, you changed the frequency.
Marcos: Yeah.
Lewin: So he changed the audio signal.
So I want you to appreciate that we really are transmitting from this antenna, by unplugging it.
[tone stops, static noise]
So now the radio doesn't see
the electromagnetic waves
[tone continues]
at eight hundred and two kiloHertz.
[tone]
So the radio is receiving now,
the radio waves that we are producing.
[tone]
Now, we're going to do something
that is not so nice.
[tone]
We're going to change our frequency
to eight hundred fifty KiloHertz.
[tone]
So now what are we going to do is jamming
the WEEA sport channel.
[tone]
So you may hear our one kiloHertz [tone]
tone but you may not hear [tone] what they
are saying.
Can we first listen to WEEI,
before we do this nasty thing?
[tone fades into static noise
followed by radio]
Radio: uh, not the, you know, Larry Dominique matchup, but he says it was not,
now what, what was the date of Clemens'...
Lewin: Is it WEEI?
Marcos: Yeah.
Radio: ...dig that up, 
do we know the date?
Lewin: Now be a naughty boy.
Radio: I've got all the, uh, the Celtics playoffs
dates here...
[radio signal replaced by tone]
We're doing something
very illegal here.
[tone]
In fact, we can do even worse.
[tone]
[tone changes pitch and silences for the most part]
I can be on the radio.
[laughter]
I'll have to turn off my microphone,
because otherwise,
you wouldn't know whether
it comes from the radio...
[Microfone off,
voice volume down]
or whether it comes
from my microphone.
[kgg, sound clearly hearable via the radio,
kgg repeated]
Hello, hello? Can you hear me?
This is radio WHTL,
it's a pirate station in the Cambridge area,
we're now transmitting
at eight hundred fifty kiloHertz.
Our weekly programs will be on the latest
excitement in science.
Of course, we realize that this is illegal as hell,
[laughter]
but that's why we like it so much.
[laughter]
We start our first program
next Monday at ten AM
and if you have any questions,
feel free to contact the Physics Department
of Harvard University.
[laughter]
See you next Wednesday.
[applause]
