When microwaving a bag of popcorn, why doesn’t the first kernel that is popped burn by the time the last kernel is popped?
In: Chemistry
Microwaves are really good at heating water. Dry things don’t heat very well compared to wet things.
When you start microwaving a bag of popcorn, almost all the moisture is inside the kernels, and so they absorb the microwaves and kernels begin to heat up. A kernel pops and becomes popcorn.
Microwaves continue to be absorbed by the kernels full of moisture. The dry popcorn is largely unaffected. Kernels continue to pop.
Eventually there are almost no kernels left, they have all popped into popcorn. Their moisture was effectively protecting the popcorn by sucking up all the microwaves, but now there are almost no kernels full of moisture to suck up the microwaves, and instead the popcorn is sitting in a cloud of super-heated vapor. The popcorn begins to burn
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