MadSci Network: Chemistry

Re: Differences in heating/cooling? Stove versus microwave.

Date: Thu Jul 29 05:50:26 1999
Posted By: Carl Custer, Staff, Office Public Health & Science, Scientific Research Oversight Staff , USDA FSIS OPHS
Area of science: Chemistry
ID: 932702660.Ch

Yes, you supplied some of the evidence; trust your own impression.  
Next, test your subjective impression with an objective measuring device, 
such as a thermometer.
But, before you run to find a thermometer, let me chat a bit about how 
stoves and microwaves differ in the way they heat. 
1. Stoves heat food by conduction: 
The electric element or the fire beneath a bowl conducts heat to the bowl. 
 That bowl then conducts heat to the food.  
2. Microwave ovens heat food by induction.
The microwaves resonate, primarily with the water and fat molecules in the 
food, thus, transferring heat directly to the food.   

Try this thought experiment: Imagine two identical bowls with the identical 
amounts of food.  Then imagine heating one bowl on the stove and the other 
in the microwave oven to the same food temperature. 
Question #1. In which heating system did the bowl receive the least heat? 
Question #2  Which dish (bowl plus food), delivered to the table, would 
contain the greater amount of heat  (BTUs, Calories, or Joules)? 
Question #3 Would the dish with the greatest amount of heat, keep the food 
warm longer? 
If you concluded that the dish heated on the stove contained the most heat 
(because the bowl had to heat the food) pin a blue ribbon on yourself for 
correctly answering both #1 & #2. 
If you concluded that the microwave heated food would conduct heat to the 
bowl, because the bowl was colder than the food, give yourself the Fourier 
Thermodynamics Medal.
If you concluded the dish with the greatest amount of heat would keep the 
food warmer longer, pat yourself on the back for logical thought and go buy 
yourself a candy. 
If you thought “duh-oh I understand” after reading the first question -- 
and you’ve still read this far, give your self the Millennium Medal for 
Patience with old mens’ corny answers to good questions. 

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