Today I almost set my dorm on fire…
Here’s the story:
I was making oatmeal in my microwave. [Classic “this-will-have-to-do” college meal.]
First, I poured into a ceramic bowl what I esteemed the optimal oat-flakes to water ratio. Sometimes I add too much water and as I heat the oatmeal, hot sludge bubbles out of the bowl and is reconstituted as a sticky crud on the microwave’s glass plate. Not today, said I, snatching a folded piece of paper from my desk and inserting it between the ceramic bowl and microwave plate. I start the microwave and busy myself with watering the cacti in my window.
Pop-pop-pop! go the contents of the microwave.
I rush over in time to see tiny bursts of flame erupt within the microwave. My oatmeal crud-catcher is on fire!! I fling the microwave open and dash out the flames, which had barely begun to eat away at the paper.
The paper now sports three interesting burn-holes of curious geometry. When I unfolded the paper, here is what I found: half a math proof and some scribbles–the largest of which had been obliterated by fire. These drawings were done with a graphite pencil.
OH, RIGHT. GRAPHITE IS A CONDUCTOR.
Let’s review why:
Graphite consists of sheets of carbon atoms locked together into a tight network. We do not typically consider carbon a conductive material (think about the conductivity of coal, or perhaps an oil, or a fatty acid), however the type of bonding network which forms between these atoms is special and allows for electrons to zip through the bonds between atoms and transmit with relative ease across the sheet. This property bumps graphite into the class of conductors, with free-flowing electrons.
When I place a conductor in the microwave, the radiation generated by the device sloshes the conductor’s free electrons back and forth inside the material, generating heat. Inside the graphite sheets, electrons go shooting across the tracks laid down by my scribbles and heat the lattice as they go screaming and crashing through the graphite network..The heat from this process was sufficient to ignite the paper the graphite was rubbed onto, and presto, we have a fire.
At least one of these experiments is worth trying at home (with a fire extinguisher nearby–safety first, guys).
Graphite animation source: “Graphite” by Saumitra R Mehrotra & Gerhard Klimeck – Crystal Viewer Tool on http://www.nanoHUB.org. Link: http://nanohub.org/resources/8795. Licensed under CC BY 3.0 via Commons – https://commons.wikimedia.org/wiki/File:Graphite.gif#/media/File:Graphite.gif