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Literally transforming sound into an actual light wave seems almost impossible. But transforming the sound wave into a light wave while containing a single mass? I know that sound can contain a mass of solid, liquid or a gas type. but does light have a mass at all? Is it possible to literally transform sound into light while containing a single mass? I have a experimental project. I want to know if it's possible in the slightest way? let me figure out how, just for the fun of the research.

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marked as duplicate by Qmechanic May 4 at 23:54

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Something like sonoluminescence? –  Raskolnikov Jun 12 '12 at 9:11
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This is basically what a microphone does. If you use the sound waves to make an electric charge oscillate, the charge will radiate EM waves at the same frequency as the sound. –  John Rennie Jun 12 '12 at 9:23
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I'm not entirely sure I understand completely your question. What I think you asked is :

  • Is it possible to transform a sound wave into a light wave?
  • If yes, is there any problem arising from the fact that sound in propagating in matter while photons have no mass?

Visible light frequencies are around 500 THz. This is many orders of magnitude faster than the typical sound wave you think of, as audible sound waves are at most 20 kHz. This means that a linear process converting audible sound to visible light at the same frequency is not possible directly.

As Raskolnikov said, sonoluminescence is an effect that will produce light from an ultrasonic wave and as John Rennie said, any microphone is transforming a sound into an electromagnetic wave. Light is also an electromagnetic wave (but typically at a different frequency). It is also worth noting that a strong and intensed light can make matter explode, producing sound waves in the process.

I think you might be interested in learning more about acousto-optic modulators as they provide a good case for an interaction between light and sound.

http://en.wikipedia.org/wiki/Acousto-optic_modulator

Not entering into details, in such a device, there is a crystal in which light interacts with an acoustic wave. A typical oscillation frequency would be for instance 100 MHz. As a result of this interaction, the light frequency is shifted by the acoustic wave frequency (or a multiple of it).

Is there any transfer of mass from the acoustic wave to the optical wave ? The answer is no, since a photon doesn't have a mass, neither before or after the interaction (never). It has however a momentum $P$ and an energy $E$, given by

$$P=h\frac{\nu}{c} $$ $$E=h \nu $$ where $h$ is the Planck constant, $\nu$ and $c$ are the frequency and speed of the light.

The energy and the momentum of the photons are proportional to their frequency. This means that when the frequency of the photons is shifted in the crystal, their energy and momentum change accordingly. Since both are generally conserved, where do the additional momentum and energy come from? From the acoustic wave itself! The mass of the crystal remains however unchanged.

As a conclusion:

  • Light and sound can interact.
  • When they do, they can exchange momentum and energy, but no matter.
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