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From: sparrow@osiris.cso.uiuc.edu
Newsgroups: sci.misc
Subject: Re: differences between sound and light
Message-ID: <4100002@osiris.cso.uiuc.edu>
Date: 5 Feb 88 21:08:00 GMT
References: <413@prlb2.UUCP>
Lines: 52
Nf-ID: #R:prlb2.UUCP:413:osiris.cso.uiuc.edu:4100002:000:2645
Nf-From: osiris.cso.uiuc.edu!sparrow    Feb  5 15:08:00 1988



>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