sparrow@osiris.cso.uiuc.edu (02/06/88)
>As I am thinking about differences between vision and audition, I would like >to know the difference of behaviour between light waves and sound waves which >manifest themselves at our everyday (Newtonian, non-quantum) scale. For >example: longitudinal/transversal waves, superposition and interference of >waves, diffraction, refraction, reflection, and absorption of waves by >objects. Don't explain me special relativity! > >Pointers to serious books or papers appreciated. Follow-up to sci.misc. > >Christian Ronse maldoror@prlb2.UUCP >{uunet|philabs|mcvax|...}!prlb2!{maldoror|ronse} Let me try a couple of things, first about human perception of light and sound. Your eyes let you see over only a small band of frequencies of the electromagnetic spectrum, the part of the spectrum that we call light. On the other hand your ears let you hear over several orders of magnitudes of frequencies of acoustical disturbances, those that we call sound. I also know for a fact that your ears are very sensitive over a large range of sound intensities, many orders of magnitude. I suspect that your eyes are not sensitive to several orders of magnitude of light intensity (how bright or dim), but I am less sure of this. Physically, assuming the air is your propagation medium, light waves are transverse waves and acoustic waves are longitudinal waves. Specifically for light the electric and magnetic field vectors are perpendicular to each other and to the direction of propagation. For sound the displacements of fluid are along the direction of propagation. In just about every case, linear propagation theory correctly describes light wave propataion. This means that the principle of superposition works well. For acoustics, however, superposition breaks down for very loud sounds. Some everyday examples of this are jet aircraft noise, certain types of helicopter noise, or the noise of explosions. For sounds less loud, linear theory holds and you get the same reflection, diffraction, and refraction effects as you do for light, just that the scales of things are different. Remember light travels at 3x10**8 m/sec and sound at about 343 m/sec. I don't know much about the properties of light other than what I got in sophomore college physics. Physics texts may help you here. For basic books on sound and acoustics some good ones are: Musical Acoustics -- Donald Hall ??? -- A. Benade Fundamentals of Acoustics - Kinsler, Frey, Coppens and Sanders For a deeper look at acoustics: Theoretical Acoustics -- Morse and Ingard Acoustics -- Allan Pierce Good luck, Vic Sparrow sparrow@osiris.cso.uiuc.edu
jwl@ernie.Berkeley.EDU (James Wilbur Lewis) (02/07/88)
In article <4100002@osiris.cso.uiuc.edu> sparrow@osiris.cso.uiuc.edu writes: >>As I am thinking about differences between vision and audition, I would like >>to know the difference of behaviour between light waves and sound waves which >>manifest themselves at our everyday (Newtonian, non-quantum) scale. > > I also know for a fact that >your ears are very sensitive over a large range of sound intensities, >many orders of magnitude. I suspect that your eyes are not sensitive >to several orders of magnitude of light intensity (how bright or dim), >but I am less sure of this. No, you're mistaken about this...the full moon is about 1,000,000 times brighter than the faintest stars that are visible without optical aid; typical sunlit terrestrial scenes are brighter still, by perhaps another order of magnitude. >For sounds less loud, linear theory holds and you get the same >reflection, diffraction, and refraction effects as you do for light, >just that the scales of things are different. Remember light travels >at 3x10**8 m/sec and sound at about 343 m/sec. This manifests itself in several observable ways...for example, the Doppler effect is significant for sound, but not light. ("But officer, that traffic light looked *green* to me...must have been the Doppler effect!" :-) And the difference between the speed of sound and the speed of light gives you something interesting to do if you're stuck in a thunderstorm.... -- Jim Lewis U.C. Berkeley