Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site lanl.ARPA Path: utzoo!decvax!genrad!panda!talcott!harvard!seismo!cmcl2!lanl!jp From: jp@lanl.ARPA Newsgroups: net.physics Subject: Re: Behavior of macaroni in a microwave oven? Message-ID: <28264@lanl.ARPA> Date: Sat, 13-Jul-85 14:45:15 EDT Article-I.D.: lanl.28264 Posted: Sat Jul 13 14:45:15 1985 Date-Received: Mon, 15-Jul-85 21:00:50 EDT References: <2970@nsc.UUCP> Distribution: na Organization: Los Alamos National Laboratory Lines: 38 > > Today, I had some macaroni and cheese for lunch(actually leftovers) which > I brought to work with me. Before eating it, I microwaved it to warm it > up. I noticed that some of the macaroni was really hot and a spot a couple > of inches away was still cold. > > This seems like really odd behavior. Any ideas why it does this? Yes. The energy in your microwave oven is electromagnetic waves bouncing around inside a closed metal box. The reflections at the boundaries result in a standing wave pattern with regions of high electric field (and, consequently, low magnetic field) and vice versa. Microwave cooking occurs from heating by dielectric loss (mostly in the water). The parts of the food that are near electric field maxima heat more than those near electric field minima. Most microwaves have a rotating metal blade that "stirs" the microwaves. That is, it disturbs the standing wave pattern in an attempt (usually not very successful) to move the electric field maxima and minima around. The rotating table in some microwaves is an attempt to even out the cooking by moving the food around in the standing wave pattern. Unforunately, the middle of the rotating tray doesn't move very far. Once, someone asked me how to measure the field distribution in a microwave oven. (He was curing some kind of ceramic glue or something like that.) Since my main job is measuring microwave field distributions in cavities he thought I was a good person to ask. He didn't seem fully satisfied with my answer, however. I suggested that he cover a pizza crust more or less uniformly with cheese and place it in the microwave oven. The electric field maxima would be at the points where the cheese first began to melt. Actually this is a tough problem because the frequency of the oven cavity and the standing wave pattern depend on the distribution of food (dielectric loading) in the cavity. If all you want to do is cook hotdogs, just apply 120VAC from end to end for 60 secs. It works, and it's cheap. Yours for scientific cooking, Jim Potter jp@lanl.arpa