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Light bulb

Bill reads from his book of fairy tales. He tells the story of the engineering of a light bulb, focusing on the materials breakthrough needed to make the filament.

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Transcript I've written a book of fairy tales. I'm going to read you one.

Once upon a time I came across the world's largest light bulb. Now I can't tell you where I found them or how I found them, but I will tell you that they are an amazing piece of engineering.

There's a fairy tale oft told about the light bulb. Edison invented it and then poof it took over the world. But there's more than just proving the concept, more than just the science. We all know that when electricity passes through filament made of high-melting point tungsten it reaches high temperatures. Now we also know that its enclosed in this glass container so that the tungsten doesn't flame out. Yet the filament shows the essentialness of engineering. It's fine to talk about how tungsten's the right material, but how do you get it? That took years of engineering.

To make the filament in a regular-sized 60 watt light bulb engineers created an amazing double-coiled thin wire of tungsten ... amazing because doesn't' easily form wire. Its not ductile. For example, this copper coil can be easily bent and reshaped - that's ductility. But a piece of tungsten will snap. Its brittle.

An engineer at General Electric devised a way to take extremely pure tungsten powder, press it together ... and then heat cool and bend it until he made tungsten ductile. Now that process isn't a scientific step its an engineering step.

Now one last thing: The bulb needs to be filled with an inert gas like argon. Without it the tungsten will burst into flame, it will combust. Now if I tap a small hole in the back here and let the gas out you can see for yourself what happens to the filament when I turn it on.