Choosing a Light Bulb Filament

Research Questions:

• How can you make a light bulb burn for as long as possible?
• Which thickness of filaments is ideal for a burning light bulb?

Ready to build your own light bulb? First, you have to figure out which filament you can use to keep your light bulb burning for the longest time. In this science project, you will build a simple light bulb and use it to test out filaments of varying thickness.

Materials:

• 3 feet of insulated copper wire
• Wire cutters
• Wire strippers
• 1-inch nail
• Glass jar with cork
• Picture hanging wire (“rope” of thin metal threads)
• Electric tape
• 6-volt battery
• Stopwatch or watch with a second hand

Experimental Procedure:

1. Cut two pieces of copper wire, each 1 ½ feet long.
2. Strip an inch of the plastic insulation from each side of the wires.
3. Use a nail to poke two holes straight through the cork, from top to bottom.
4. Push the end of one of the wires through one of the holes so that about two inches protrudes from the bottom. Do the same with the second wire in the second hole.
5. Bend the two wire ends that are protruding from the bottom of the cord to make small hooks. The filament will connect to these hooks.
6. Untangle the individual wire threads from the picture hanging wire. Twist two of the threads together to make a filament.
7. Use the filament to connect the two wire hooks sticking out from the bottom of the cork. To do this, twist either end of the filament around one of the hooks.
8. Place the cork stopper into the mouth of the jar.
9. Use electric tape to attach one of the free ends of the wires to the positive terminal of the battery and one to the negative terminal.
10. Immediately start your stopwatch. Your homemade “light bulb” should light up.
11. Record exactly how long the light bulb filament glows.
12. Remove the wires from the battery’s terminals. Wait two minutes for the filament to cool, and then remove it from the light bulb.
13. Repeat this experiment using a new filament made from two strands of wire.
14. Create a filament out of three strands of wire. Repeat the experiment two times using this filament instead.
15. Create a filament out of four strands of wire. Repeat the experiment two times using this filament instead.
16. Create a bar chart to show the average amount of time it took for each light bulb to burn out. Which filament worked best?

Terms/Concepts: Filament; How does a light bulb work?

References:

First Place Science Fair Projects for Inquisitive Kids, by Elizabeth Snoke Harris. Pp. 70-71.