Experiment 7

Edison’s Electric Light

Materials: Wide-mouth jar with cover. 4’ of hookup wire. Copper-strand lamp wire 4” long. Switch from Experi- ment 4. Birthday cake candle on a small base. 6-volt battery.

     BULB. In the cover, punch two small holes just big enough to receive the wire. Space the holes 1-1/2” apart. Insert two 18” lengths of wire through the holes so that they will extend halfway into the jar. Now bend the wires down the sides of the cover, and tape them in place. Put a strip of tape over the holes too.

     FILAMENT. Remove one copper strand from the lamp wire. Wind it several times around a nail. Slip the coiled filament off the nail, and connect it to the two wires coming from the cover.

     LIGHTING UP THE DARK (WELL, NOT QUITE). Screw the cover on the jar. This is our “lamp.” Next, connect the lamp in series with the switch and the battery. Turn the lamp on and start counting. The filament will begin to glow. If it continues glowing for more than 15 seconds, open the switch. Otherwise you’ll drain the battery. Try a shorter filament. Keep doing this until you find a length that burns for just a few seconds. When you do, put on a new filament of this length.

     Now we’re going to remove some of the air from the lamp. Put the candle inside the jar and ignite it. There turn out the room lights. While the candle is burning, close the jar tightly. When the candle goes out, which means it has used up a lot of the air, turn the lamp on once again.