Coffee, Cups, and Microwaves
Name: John W.
Date: June 2003
Why do coffee cups seem to get hotter in a microwave when used to heat up water?
When the cup is first used it does not feel hot. A few months later (after daily use in the
microwave at breakfast or tea) the cup is too hot to touch. Why is this so?
Interesting observation. I do not know that your observation has been tested experimentally,
but it should be. A working hypothesis to start with might be that the cup material (if it is
ceramic) is absorbing water. Microwave ovens are "tuned" to frequencies absorbed by water
molecules. It could be that the cup material is "picking up" water somehow. I do not know
whether some hydrate may be forming, or whether micro-cracks and crevices are forming that
allow water to permeate the cup. If some preliminary experiments supported your observation
this would make one fine science fair project!!!!
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Update: June 2012