Video recorded in 2007.

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

Sun light or torch is reflected off a flexible shiny surface fixed to the end of a plastic tube.  When one speaks into the tubes 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 - we have 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!
 

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 Links To Other Information:

Light Beam Article
Article to be used with this film

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