Light Radio

Materials: radio, amplified speaker, solar cell, red

LED, mini plugs, wire, power supplies, various lenses and filters.

Building Instructions: Attach mini plug to wire and LED to other end. Plug into headphone jack. Attach mini plug to wire and solar cell to other end. Plug into input on the amplified speaker. Turn on radio and speaker. Aim LED toward solar cell and adjust volume until you hear the station clearly.

Function and Use: This demonstration shows how energy can be transformed into sound. Radio waves (in this case from a radio station) enter the radio through an antenna and are changed to electricity by circuits inside. This electricity normally powers a speaker, but on this set-up it powers a special ‘bulb’ that gives off red light. If you look closely you can see the bulb’s brightness change in response to talking and music. This light is then shined onto a ‘solar cell’ and changed by the cell back into electricity. This is then fed into a speaker. Remember that lights and sunlight in the room interfere with the solar cell and all of the light is changed to electricity not just the red light’s signal. Put your hand in between and open your fingers to let some of the light through – what happened? Try some of the lenses and see if you can make the sound clearer or louder. Try the polarizing filters – hold one and then rotate the other one around and see what happens. Try the Fresnel lens (the square piece of plastic) and focus the light on the cell and see what happens.