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Q: Light and Sound ( No Answer,   8 Comments )
Subject: Light and Sound
Category: Science
Asked by: azdoug-ga
List Price: $2.00
Posted: 30 May 2006 10:45 PDT
Expires: 29 Jun 2006 10:45 PDT
Question ID: 733700
Is there a medium through which light (being seen as a wave) and sound
waves travel at the same frequency?  What about frequencies that are
relatively close harmonics to one another?

Basically, is it possible to produce a sound that would resonate with
light and possibly vibrate the medium through which they're both

Clarification of Question by azdoug-ga on 30 May 2006 12:35 PDT
Wavelength is only helpful if you have the velocity of the wave...

Velocity/wavelength = frequency... right?

We know the speed of sound (or light) changes through various mediums,
so therefore, the frequency must also change.

Wavelengths are dependant on whatever is generating the light/sound --
they are independant of the medium.
There is no answer at this time.

Subject: Re: Light and Sound
From: toufaroo-ga on 30 May 2006 11:55 PDT
Technically, the FREQUENCY of light/sound never changes.  It is what
characterized that color/pitch.

However, the wavelength can and does change.  Conceivably, it might be
possible to have light and sound of the same wavelength!

We know from any basic physics class that sound generally moves faster
through denser materials.  It doesn't propagate at all in a vacuum,
travels somewhat fast in air, travels really fast in metals.

Light seems to work oppositely.  It travels the fastest through a
vacuum, slower in water, slower yet in a diamond, etc.

Now, let's look at typical wavelengths of light/sound in air.

For a yellow light, you're looking at about 550 nm. (That's 10^-9
meters)  For typical human speech, you're looking at a range of 100 -
8000 Hz, so let's assume an average frequency of 4000 Hz, and that
corresponds to a wavelength of  roughly .09 m or 9 x 10^-2 m.

That means you would have to find a material that was so dense as to
allow for sound transmission at speeds on the order of 1000 times
faster than the speed of sound through air.  This same material would
have to slow light down by a factor of 1000 for you to even come close
for the light and sound to have the same wavelength.  Oh, and it has
to be optically clear.

On earth, we have no such material.  If you broaden your definitions
of light and sound to include microwaves, short waves, etc. and
ultrasonic frequencies, then you narrow the gap significantly.
Subject: Re: Light and Sound
From: philnj-ga on 30 May 2006 12:20 PDT
With all due respect.  I think that toufaroo's comment is missing some
important concepts.
Subject: Re: Light and Sound
From: stanmartin1952-ga on 30 May 2006 23:28 PDT
Light is an electomagnetic wave; whereas, sound is a pressure wave.
You could build a circuit with a sound output that would vary
according to the light striking a photodiode. You could also build a
circuit with a light output that would vary according to the sound
reaching a microphone.
Subject: Re: Light and Sound
From: toufaroo-ga on 02 Jun 2006 10:28 PDT
The frequency/wavelength thing is a common misconception; the
frequency of a electromagnetic wave (let's assume light) identifies
its color.  This characteristic is independent of medium.

In common use, light is referenced in terms of its wavelength.  For
instance, you might say that a particular red light has a wavelength
of 630 nm.  What you're technically saying is that through AIR, this
frequency of light has a wavelength of 630 nm.  The frequency is the
"fingerprint" if you will.  As the medium changes, frequency remains
constant but wavelength changes.  This is true for both light and

Having said all that, I agree with philnj that my earlier comment was
not really complete.

Technically, you could through air, have a pressure wave that vibrated
on the order of 10^14 Hz (same as visible light).  However, the
resulting pressure wave would be way beyond the human threshold for

Sound is a pressure wave, while light is an electromagnetic wave, two
completely different things.  But your use of the word "frequency"
just means cycles/second and applies to both light and sound.

Now whether the sound and light would interact with each other, the
simple answer is no.
Subject: Re: Light and Sound
From: ashaman5-ga on 10 Jun 2006 15:33 PDT
sorry to sound harsh, but toufaroo has really invented his own branch
of physics now.  his entire line of commentary i find physically
inaccurate and a intricate mix of confabulation and google searches
for physics, but this statement in particular should raise eyebrows
all around:

As the medium changes, frequency remains constant but wavelength changes.

any entry level physics student knows that the frequency and
wavelength of an electromagnetic wave are inversely related.  c = fw 
(sorry, no greek symbols allowed on google answers)   c is the speed
of light (a *constant*!), f is the frequency of the wave, and w is the
wavelength.  it is IMPOSSIBLE to change the freqency of a wave without
altering it's wavelength.  (except, i suppose, in toufaroo's world)

please disregard all of the nonsense he or she has written as little
of it has any basis in contemporary physics.  i won't even bother to
comment on the well-known wavelength dependence of the index of
refraction, etc. which toufaroo has sincerely overlooked.

caveat emptor on google answers.

to actually answer the question, it is in principle possible, although
it would probably require propagating the light and sound through a
really exotic medium (like the resonant states in BEC's that Lene Hau
at harvard used to "slow" light down to 20m/s).  that sort of stuff
might do the trick, although one would need to calculate what sound
velocities would be like in that medium.
Subject: Re: Light and Sound
From: mabedana-ga on 15 Jun 2006 15:23 PDT
the bases are diffrent
the base of sound is to chenge the capacity of the air
but the base of light is to product a frequent of electrons or etc.

!! !  !  ! !!! !  !  ! !!! !  !  ! !!! !  !  ! !

      -      -       -   
\   /   \  /   \   /   \
  -      -       -      -
Subject: Re: Light and Sound
From: ashaman5-ga on 17 Jun 2006 20:10 PDT
clearly mabedana has never, ever heard of optical phonons!

or transverse phonons, in general (be they acoustic or optical)

please, mabedana and toufaroo, do *not* spam google answers.  if you
have no comprehension of a topic, don't offer your misguided opinion. 
it's just spam for the others to sift through.  and downright
misleading, besides.
Subject: Re: Light and Sound
From: toufaroo-ga on 13 Jul 2006 09:23 PDT
Listen here, ashaman5...No comprehension of a subject?!  I have an MS
in engineering.  Don't tell me I don't know what I am talking about.

Listen here mate - you CANNOT change the frequency of a light wave by
simply having it pass through different mediums.  c = fw...fine.  But
the frequency establishes the wave color.  It must remain constant, or
you'd have red light entering a medium, blue light leaving it.  So,
that means w and c change accordingly but f remains constant.

Yes, it may sound weird, but the speed of light DOES change as it
passes through different mediums.  (this, by the way, is where your
'index of refraction' thing comes into play)  That's why the 3 x 10^8
value is specifically defined for a vacuum.

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