How do we put our voice on a light beam?

Here Jonathan demonstrates how sun light or torch light can be reflected off of a flexible shiny surface fixed to the end of a plastic tube and then when one speaks into the tube sound vibrations pass down the tube and make the surface vibrate.  The reflected light is therefore sent off from the surface in a continuously changing set of angles depending on the loudness and frequencies of the voice.  The light is said to have become modulated by the sound and we could say that we have therefore put our voice on a sunbeam!  Getting the sound back (demodulation of the light beam) is also very simple.  A solar cell is attached to a speaker amplifier.  As the light intensity is changing with the voice so the signal from the solar cell changes.  When amplified and sent to a speaker (a device that turns voltage into sound) one hears the original voice again!

This video should be used with the following article: Light Beam (Link below)

Light Beam Article
Article to be used with this film

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