Thursday, April 17, 2014

Homemade Light Bulb

This activity was really, really fun, and quite spectacular to watch. On the day we learned about Thomas Edison, we made our own light bulb! I didn't even know you could do that. But all you need is some electricity (8 D batteries), a holding apparatus of some sort, and a resistant material (mechanical pencil leads work perfectly). Thomas Edison, we read, tried something like 1000 different materials before coming up with a practical light bulb, so don't give up if this doesn't work the first time. :)
First, rig up your apparatus. You are just making a circuit with the pencil lead in the middle of it. So tape an alligator clip to one end of your line of batteries (which should be taped end to end), and run the other end of the wire up one side of a toilet paper tube or something similar. Clip one end of the pencil lead carefully into the "jaws" of the clip. Attach another alligator clips's jaws to the other end of the pencil lead, run the wire down the other side of the toilet paper tube, and tape the other end of the second alligator wire to the other side of the batteries, forming a complete circuit. Now your pencil lead should be suspended like a filament over the top end of the toilet paper tube. Put a glass jar upside down over the top of the whole thing.
As electricity runs through the circuit, the pencil lead will resist the current and begin to heat up and glow. This doesn't take very long (a minute, maybe?) so if doesn't start happening soon, check your circuit with a tiny light bulb or something, to make sure all the batteries are touching each other and none of the wires are faulty. It should start to smoke a bit and then glow quite beautifully.
After a short time, the pencil lead will glow very brightly and then get too hot and melt. It will break apart, opening the circuit, and that's the end of your light bulb. But you can always put in a new pencil lead and try it again and again! :)
The children were just mesmerized by their glowing homemade bulbs (and they liked the smoke and the flash as they burned out, too). This was definitely a favorite activity!

When we went to the science museum in Portland, Oregon recently, we got to see one of Edison's original bulbs (one of the ones that didn't work very well). We also saw a model of the successful bulb he made later. It was really cool to see!

Here's a video about Thomas Edison.

Speaking of Edison, here's a video that talks about the differences between AC and DC, and the contributions of Edison and Tesla to each.

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