User talk:Jasonkeirstead

Heating Water and water containing substances in a microwave
I removed the blip about water heating the best in a microwave because it needs clarification (and was already marked as needing citation, and since I pretty much know it is incorrect). While water may be the "heat source" for most foods cooking in a microwave, it is certainly not the "most efficient" heater, especially when you are talking about say, a cup of pure water. For example, a cup of water and a cup of milk at the same temperature, the milk will boil first. My theory (with no references to back it up) is this is because all the water molecules are experiencing the dielectric effect at almost the exact same moment, so not as much heat occurs as when they are intermixed with other molecules which do not exhibit the effect to the same degree.Jasonkeirstead (talk) 11:03, 28 August 2008 (UTC)


 * What heats "best" is not a very clear thing. Water absorbs energy better, but it may not heat as fast, simply because it doesn't have as large heat capacity, so it absorbs more energy but doesn't go up as much in temperature. As an example, I had to try your milk experiment, so I took two 80 mL samples of water and milk in identical beakers and and stuck them here into the lab kitchen GE microwave, both thermocouple measured at exactly 24.5 C before they went in. After 10 seconds on "high" (both of them together, placed at exactly equal spots on either side of the rotating table, equidistant from center to edge) the water had gone up 7.3 C and the milk 7.8 C after taking them out and mixing and letting them equilibrate for a couple of minutes. Ha, the milk was heating 6.8% faster. And my microwave was putting out about a bit more than 500 watts, which is about right. After another shot of 15 seconds (I made sure the milk and water traded places on the rotating glass bottom for this one) the milk heated by 12 C to a total of 44.3 C, and the water heated by 11.4 C to a total of 43.2 C. So again, the milk is heating 5.2% faster. (And both samples heated about 50% more, in keeping with the 50% increase in time, so the experiment is going well). But hold on, there! First, I have a total of 19.8 C heating for the milk, and 18.7 C heating for the water, so on average, the milk beat the water in heating by only 19.8/18.7 = 1.059 = 5.9%. Not much! I can't reliably measure volumes in beakers that well! (I should have used a graduated cylinder, but I'm ruling out first order effects). Second, there's a bigger problem, which is that milk isn't pure water. I used skim milk, which has 13 grams of sugar and 9 grams of protein in 240 mL (according to the label) so it's only about 91% water. So it's not surprising if it only has 1/1.059 = 94.4% of the heat capacity of pure water. All that is required is that the milk solids, the sugar and protein, have 3.3/9 = 37% of the specific heat capacity of the water they replace in the milk. Which isn't hard to believe at all, since water has so high a specific heat capacity. So, all in all, we're both doing original research, but the effect you report is very small, and is easily explained by the fact that water has a higher specific heat capacity than the stuff you're replacing it with, in a food-mix, or even in milk. But the water is doing most of the microwave absorption, just as advertised by the texts. S  B Harris 04:08, 21 January 2009 (UTC)