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Reprinted by permission of Dick Berg, University of Maryland, for use on this website.

The demonstrations contained and referenced herein are listed for the purposes of cataloging and describing physics demonstrations which should be conducted only under the direction of a trained instructional support professional or physicist. These demonstrations are not presented for the purpose of being conducted by persons unconnected to this Facility and/or persons not consulting with or being supervised by the recognized instructional support professional or physicist and his/her staff. The University is responsible only for those demonstrations carried out using its own equipment using established safety and scheduling policies, and bears no responsibility for those choosing to use this source material for their own purposes. All demonstrations described and contained herein are public domain, and can also be found in reference materials in libraries, bookstores, and electronic sources.

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Plug the LED into the portable tape player and connect the battery pack.  Then also plug the photocell into the Radio Shack speaker amplifier.  The modulated light signal given off by the tape player can be picked up with the photocell.

Plug the earphone jack of the radio or the wave generator into the modulated laser. Caution should be observed that an amplified signal is not put into the laser as anything above 1 volt peak to peak will burn out the modulating transistors in the laser. Also note that the laser can only be modulated to frequencies of 1 MHz. without severe distortion. Plug either the photovoltaic cell or the LSR into the homemade pre-amp and plug the pre-amp into a speaker. Focus the laser beam onto the detector that you have chosen. Sound should now be transmitted via laser beam to the pre-amp/speaker assembly. 

The modulated laser may be replaced with the portable tape player and the LED and battery assembly. The batteries light the LED and by plugging into the earphone jack of the tape player you modulate the LED output. This signal may be picked up by either the LSR or the photovoltaic cell in the same manner as the laser setup. A fiber optics cable may be used transmit the LED signal to the photocell or LSR.