Sunday, March 18, 2012

I met up with Rachel and Puja (and their spouses) yesterday in Arlington. It was a good time, and we didn't spend the whole time arguing but I did receive a lot of criticism for my practice of microwaving chinese food without first removing the metal handle.

I feel like Puja knows the theory involved but has unrealistic expectations of this practical application. And Rachel tried to convince me with a lot of cautionary webpage quotes and videos of exploding tin foil. Everyone thought my reasoning was hilariously unrealistic, much like when I tried to explain to Eric and Dave why birds don't get electrocuted on the power lines and they accused me of making things up. But, just like then, I'm still right.

A good title of this blog entry, if I were still titling entries, would be "Vindication!!!"

So a microwave works by directing microwaves into the little food chamber. The microwaves bounce around in there until they are absorbed by water and wet-ish foods, or they hit a metal object and the microwave either is reflected or is absorbed to electrically charge or heat the metal objected (which also causes reflections), or if the microwave chamber is empty they just bounce back and forth until your microwave burns out due standing wave feedback. Metal objects that fold back on themselves (like crumpled tin foil or the tines of forks) will easily spark and burn or melt, and metal objects that can't spark back to themselves (like a knife) will accumulate more and more charge until they can spark all the way to the microwave walls or ceiling and cause damage to your appliance.

The chinese food container has a metal handle that's just a heavy wire wrapped into loops at both ends where it holds the paper container. Put in the microwave, the loops at each end will create little sparks where the metal loops, and it might singe the paper container a bit and get the metal handle hot.

The middle/top of the metal handle may develop a slight net charge but it is insufficient to create a spark to the walls of the microwave because most of the charge is dissapated by the frequent looping sparks at either end and the chinese food itself (condensation inside the food container which means the handle isn't well insulated from the food) will slowly also bleed off electrical charge from the handle. Any microwaves reflected by the metal handle will bounce around a bit more but they won't cause much feedback into the magnetron because they'll be absorbed by the chinese food. (The capacitance of the entire "handle plus damp food" system is too large for it to develop a charge that can cause a spark to the wall to damage your microwave. It's like putting two piles of spaghetti on a plate and dropping a knife on top such that it has one end in each pile. Then microwaving the plate. No sparks will result because the spaghetti has too much capacitance.)

Net result: I save 30 seconds of struggling to unbend and remove a chinese food handle, and my microwave experiences exactly the same wear and tear as heating up the chinese food without the handle. (Once I did burn my hand by grabbing the handle too quickly. You just gotta be slightly more careful.) The next time I get chinese food I'll videotape it being microwaved and we'll see.

Update: You might have read "vindication" and assumed that I had evidence and not just reasoning based on assumptions and approximations. But that's not how I roll.

me: Hi, I'm calling for Chris _. Is he available?
Lady: Will he know what it's regarding?
me: Umm, no, would you like the case number?
Lady: Sure, then I can get the file for him.
(I give her the case number and get put on hold)
Chris: Yeah?
me: Hi is this Chris _ ?
Chris: Yeah. I just got handed your file. Let me look through it for a second to see if I can remember it.
me: Sure, no problem.
(30 second pause)
Chris: Okay, I don't remember this at all. Let's see what you've got.


Rachel said...

I feel like you characterized this whole situation wrong. I was the one who knew the theory behind it all!!! Thanks for doubting my knowledge :( I did look up all the web quotes and videos though. DONT MICROWAVE METAL JOE

joe said...

Sorry to mischaracterize you. I just remembered you and all those youtube videos. Anyway, it's perfectly fine to microwave metal so long as you have other food in there (not wrapped in metal), and you don't microwave metal of a configuration that will spark in ways you don't want. I'm so right on this.