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 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 traveling?``` 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.```
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 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 sound. 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 hearing. 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. sound: !! ! ! ! !!! ! ! ! !!! ! ! ! !!! ! ! ! ! light: - - - \ / \ / \ / \ - - - -```
 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.```