Recording modulates laser beam which hits solar cell and amplifier.

Recording modulates laser beam which hits solar cell and signal is amplified. An audio signal from a small portable tape recorder is plugged into the video-jack of a laser specially built to have its light intensity modulated by the changing amplitude and frequency of sound wave forms. A hooded silicon solar cell at the opposite end of the lecture table receives the modulated light beam, converting it, once again, to an electrical audio signal which is then amplified and sent to a speaker for the class to hear. Placing an object in the beam will interrupt the sound.