|MadSci Network: Physics|
You have the clue to the actual result with your question. What acually happened is due to the following set of occurences. The filiment,that usually causes the filaments of plasma was destroyed by the microwave plama het very quickly. The filament support broke and fell as as a small chunk onto the glass of the bulb. Air had replaced the vacuum during this experiment,eliminating the vacuum. A vacuum interacts well with microwave energy, allowing a plasma to form. With the vacuum gone, the microwave energy looks for the next best target. The nex best target was a clump of glass or ceramic or both. The ceramic is the material that holds the filament in place at the bottom of the bulb. With the vacuum gone, the microwave finds a clump of material that has a low thermal conductivity (ability to lose heat by conduction) and starts putting its energy into it. The energy goes in fast enough to cause the temperature to rise to the glass's melting point. This is hard to do, because small objects lose heat quickly. Molten glass is a much more effective absorber of microwave energy, so when even a small amount of glass has melted, it melts much more quickly. That's when the light show started. How can one reproduce this? With a lightbulb, this would be difficult. I piled some broken window glass on some clean, white sand inside a PYREX beaker. The glass shards heated up after some time and eventually produced the same results you described. I have done this in a laboratory environment, so DO NOT DO THIS AT HOME. A fire could result with the high temperatures you will be reaching. Molten glass may be the hottest substance you ever encounter in your life, so do not touch the glass, even with oven mits. I stopped the experiment within seconds of seeing the glass start to melt. I do not recommend that you do this experiment. I simply point out that I have seen the same effect you describe. Dr. Ed Peterson.
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