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Q: Relationship between soundwaves and lightwaves? ( Answered 4 out of 5 stars,   4 Comments )
Subject: Relationship between soundwaves and lightwaves?
Category: Science
Asked by: jat-ga
List Price: $15.00
Posted: 28 Sep 2002 15:52 PDT
Expires: 28 Oct 2002 14:52 PST
Question ID: 70246
Is there a relationship between sound waves (including ultrasound) and
lightwaves?  More specifically, I'm thinking about "harmonics" (what
little I know of it), wherein I wonder if you could take a particular
light frequency and keep dividing it by 2 until you reached a
frequency in the audible range, thereby establishing a real
relationship between the two (Where would "sound" fit on a spectrum
chart with radiowaves, lightwaves, etc.?  Please keep references in
layman's terms!  Thanks.
Subject: Re: Relationship between soundwaves and lightwaves?
Answered By: nauster-ga on 29 Sep 2002 01:43 PDT
Rated:4 out of 5 stars
Light, radio waves, X-rays, microwaves, and gamma rays are all the
same type of thing. They are all streams of photons, and the only
difference among all of them is how much energy is in the photons. All
of these photon-streams are part of the “Electromagnetic Spectrum”
that you refer to in your question.

Electromagnetic Spectrum:

Sound, however, is not a photon stream. It is a name we give to a
compression wave that travels through some medium (usually air.) A
compression wave is a series of alternating high-pressure and
low-pressure regions, and this alternation of pressure causes our
eardrums to vibrate, which our brains are wired up to interpret as

Nice visual of what a compression wave is like:

When we talk about the frequency of a sound, it is straightforward
what we are referring to. It is the number of times that the
compression wave alternates between high and low pressure in a second.
20 times a second seems very fast, but it is actually the lowest
frequency that human ears can detect. 20,000 times a second seems
impossibly fast, but that frequency can still be heard by most humans.
Middle C is a vibration of around 260 Hz (260 times a second.)

When we talk about the frequency of a photon stream, it gets
confusing. That’s because of the crazy nature of light and other
electromagnetic waves. We’d have to get into Quantum Mechanics to
fully explain it, but the short answer is that it is convenient to
think of light as a wave to explain certain things that it can be
observed to do.

You may have heard or read of the “wave-particle” dual nature of
light. Light and other electromagnetic waves are composed of photons
(particles), and aren’t REALLY waves, but can be observed doing things
that can only be explained by modeling them as waves. If you want to
get deeper into that aspect of things, here is a decent starting

As far as the frequency of electromagnetic waves is concerned, the
numbers are quite high. Radio waves are the longest, lowest-frequency,
electromagnetic waves there are, and they have a frequency of around 1
million Hz. Visible light has a frequency a BILLION TIMES more than
radio waves. So not only are sound and light two totally different
types of waves, but their frequencies are also very extraordinarily
far apart.

I expect there may be portions of this you want to explore further or
want to have explained in a different way. Please don’t hesitate to
post a clarification request. Light is a tricky topic.


Google searches used:
electromagnetic spectrum
Hz "middle c"
wave particle introduction

Clarification of Answer by nauster-ga on 29 Sep 2002 01:48 PDT
By the way, here is a link to a page that talks about the math of
music, including harmonics:

Request for Answer Clarification by jat-ga on 30 Sep 2002 09:43 PDT
I understand some of the differences between EMF and sound, which you
discuss.  However, my question still remains.  For example, let's
assume a monochromatic light to be striking the head of a snaredrum. 
Theoretically, at least, isn't it correct to assume that, although it
may be too rapid to easily measure (certainly, to hear!) there is a
compression/release/compression which occurs as the photons strike the
drum with their own characteristic frequencies?  Now, if this light
frequency was divided by 2 over and over again, wouldn't we eventually
reach a frequency that would be a harmonic and be within the audible

Clarification of Answer by nauster-ga on 30 Sep 2002 12:57 PDT
Electromagnetic waves do indeed cause certain things to vibrate, but
your snaredrum example won't work in practice. The problem is that
electromagnetic waves tend to shake things that are the same size as
their wavelength.

Radio waves are low-frequency and therefore very long: 1 to 100
meters. Now, you can have an antenna that is shorter than the
wavelength, and it will work OK if the signal is strong. But the
perfect size is the same as the wavelength of the wave you're trying
to receive. Incidentally, this is why AM radio stations use huge
antennae to broadcast their signal.

The wavelength of visible light is about the size of bacteria.
Something as large as a snare drum would not vibrate at all in
response to a beam of light. Even something as large as a single cell
would be too big to be an effective receptor of light waves.

But let's put the practical problems aside and just talk

Using this chart of the frequencies of musical notes:

I kept going up octaves by doubling the frequencies until I got to
numbers that were in the same range as visible light. Usually colors
are referred to by their wavelength instead of their frequencies, but
we can get wavelength from the frequency by the formula

wavelength = speed of light / frequency

The wavelengths of visible light are from approximately 400 - 700 nm

Here's a picture of the visible spectrum:

And here's my chart of frequencies 40-41 octaves above middle C:
F#44 = 737 nm(Infrared)
G 44 = 696 nm(Red)
G#44 = 657 nm(Red)
A 44 = 620 nm(Red-Orange)
A#44 = 585 nm(Yellow)
B 44 = 552 nm(Green)
C 45 = 521 nm(Green)
C#45 = 492 nm(Green-Blue)
D 45 = 464 nm(Blue)
D#45 = 438 nm(Violet)
E 45 = 414 nm(Violet)
F 45 = 390 nm(Ultraviolet)

In other words, if you generated a sound with the same frequency as
the green color that has wavelength of 521 nanometers, you'd have the
C 41 octaves above middle C. Looks like the visible spectrum
corresponds to just shy of a full octave in range.

jat-ga rated this answer:4 out of 5 stars
Thanks for the effort.  It has been helpful.  I may have more to ask
as I ponder your replies...

Subject: Re: Relationship between soundwaves and lightwaves?
From: random1-ga on 29 Sep 2002 06:16 PDT
I am not an expert on this topic so I would not consider my answer and
comments the unquestionable truth, but I remember enough of past study
that I can offer some guidance.

Sound and light are fundamentally different.  Sound is the vibration
of molecules (typically air (though there is no "air" molecule, of
course), although you can certainly hear through water - trying
yelling to someone while you're both submerged in a pool, or through
solids such as your own head - the fact that your head conducts sound
is largely why your voice sounds so different to you as opposed to
other people or a recorded version of your voice.)

As such, sound travels through a medium and is not a physical entity. 
A vibrating object, such as a human vocal cord, violin string,
saxophone reed, or a "speaker" produces sound.  As a side note, humans
can hear approximately 20 Hz to 20,000 Hz, where 1 Hz is one vibration
per second.

Another term for light, electromagnetic radiation, makes its
composition more clear.  While light behaves as both a particle and a
wave, it is a "thing" that can be transmitted through empty space
(such as light travelling from the sun to earth).  In empty space,
there is no sound since there is no medium to conduct vibrations from
the sound source to your ear, or a microphone.

So, sound is simply a vibration of molecules, while light is a
distinct physical entity that can be created and destroyed,
absorbed/converted, etc.

The primary similarity between light and sound are their behavior as
waves.  As such, they can both be reflected (by a mirror or a canyon,
respectively), have frequencies of oscillation while can be measured
as the color of light (or x-rays, etc. below the visual range) or the
pitch of sound (observe the difference between an inaudible dog
whistle, a doorbell, or a fog horn), and much more.

As for what happens when you change the frequency of vibration -
molecular vibration can range from the inaudibly low sounds of
long-distance elephant calls to the immensely fast vibration of atoms,
used to time precise clocks - e.g. a quartz watch or cesium as used in
atomic clocks).  As you change the frequency of "light" you range from
high-frequency gamma rays emitted by radioactive materials to x-rays
to ultraviolet (the kind that "burns" your skin) to visible light to
infrared (many remote controls operate in this range) to microwaves (a
kitchen "Microwave" is tuned to the vibrational frequency of water --
allowing you to convert "light" to "sound" very loosely speaking) all
the way to low-frequency radio waves that travel vast distances and
broadcast everything from Jazz Fusion to Mozart to the world.

Sorry this comment is a little meandering, but it's free, after all.
Subject: ULF, ELF and VLF
From: ulu-ga on 29 Sep 2002 16:28 PDT
Both nauster and random1 explained the difference between sound and
electromagnetic (EM) radiation.  There are bands of EM that would be
considered in the "audio" range.

International Band Designators
ELF extremely low frequency 3 to 30Hz
SLF superlow frequency 30 to 300Hz
ULF ultralow frequency 300 to 3,000Hz
VLF very low frequency 3 to 30kHz

(or maybe)
Ultra Low Frequency (ULF, 3-30 Hz)
Extremely Low Frequency (ELF, 30-300 Hz)
Voice Frequecny (VF, 300-3000 Hz)
Very Low Frequency (VLF, 3-30 kHz)

There are occurences of very low frequency (VLF) EM waves.  Some occur
naturally from lightning (whistlers), auroras, meteors,

These bands have also been looked at for long distance communication.

Radio waves below 22 KHz

Some people have other ideas about these frequencies.

Most of the site are fairly technical, but you can get some idea of
how these low frequencies are used.
Subject: Re: Relationship between soundwaves and lightwaves?
From: mike_r-ga on 03 Oct 2002 20:57 PDT
We convert audio frequency photons into sound all the time.

This is one way to view what a stereo does (or a buzzing transformer).
In both cases the EM propagates at the speed of light and has all the
other characteristics of photons.

However, we don't really utilize the "traditional" "photonic" effects
for these signals.    Much of what we
think of as "lightwave" effects are resonance phenomenon (such as
ejecting an electron or tuning in
KROC).   That is why antenna size is a function of wavelength.

For audio frequency lightwaves, we rely less on resonance effects and
more on the field strength of the
lightwave.   We use very high field strengths -- and systems (like a
speaker coil or transformer casing)
that can track the field strength faster than it is changing.

We also convert sound into photons (via microphones) but, again, we
are more interested in field
strengths than in the traditional "photonic" properties of the signal.

Lastly, there is the phenomenon of Sonoluminescence whereby sound
somehow (┐harmonically?) induces
light pulses in liquids.
Subject: Re: Relationship between soundwaves and lightwaves?
From: omnismiley-ga on 07 Dec 2002 08:55 PST

Simplified comparison of light and sound:

The physics of tying light to sound:

An interesting effort to tie the light spectrum and sonic spectrum together:

And if you are curious about real "projects" that will produce sound
from light (light-to-sound converter):

Looking at your question backwards, you might consider the following:

Sonoluminescence, the process from converting sound to light

Commercial sound-to-light converter: 

And an exact placement of sound in the RF spectra (if they were the same)
["rf spectrum"]:

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