# Why does metal react the way it does in a microwave? **URL:** \ **Category:** Factual Questions\ **Created:** [May 8, 2005, 2:13am UTC](https://boards.straightdope.com/t/why-does-metal-react-the-way-it-does-in-a-microwave/302888 "2005-05-08T02:13:47Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![maplers](https://avatars.discourse-cdn.com/v4/letter/m/5f9b8f/32.png) [@maplers](https://boards.straightdope.com/u/maplers)\ **Post date:** [May 8, 2005, 2:13am UTC](https://boards.straightdope.com/t/why-does-metal-react-the-way-it-does-in-a-microwave/302888/1 "2005-05-08T02:13:47Z")
Just a simple question, self explanatory. Why does the radiation do that to metal? ---
**Author:** ![rfgdxm](https://avatars.discourse-cdn.com/v4/letter/r/c0e974/32.png) [@rfgdxm](https://boards.straightdope.com/u/rfgdxm)\ **Post date:** [May 8, 2005, 2:18am UTC](https://boards.straightdope.com/t/why-does-metal-react-the-way-it-does-in-a-microwave/302888/2 "2005-05-08T02:18:03Z")
It reflects radio energy at that frequency. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [May 8, 2005, 3:48am UTC](https://boards.straightdope.com/t/why-does-metal-react-the-way-it-does-in-a-microwave/302888/3 "2005-05-08T03:48:49Z")
I guess the easiest way to explain it is that your microwave is basically a big radio transmitter. All of the radio waves go from the magnetron (a little thingy that spins around and makes radio waves), through the waveguide (a metal tube) and into the chamber. Instead of being broadcast out like a radio station you would listen to, the radio waves just bounce around in the chamber until they get absorbed by something that is inside the chamber. This is why you shouldn’t turn on a microwave with nothing inside it. There’s nothing to absorb the radio waves and they can end up bouncing back into the magnetron and damaging it. So, what you have is a chamber with radio waves bouncing all around in it, and you put a piece of metal inside it. The metal is going to act is kind of a radio antenna, only its not tuned to the precise frequency of the microwave oven. Since its not tuned, some of the radio energy will get absorbed and some of it will get reflected back away from the metal. The energy that does get absorbed will cause currents to flow through the metal, which if the metal is thin enough could cause it to heat up significantly. Depending on the shape of the metal the energy could cause charges to build up and jump across gaps, making arcs of electricity that you can see. Steel wool and CDs (which are made of a metal foil on plastic) make for rather impressive light shows because of this. ---
**Author:** ![Washoe](https://avatars.discourse-cdn.com/v4/letter/w/ecae2f/32.png) [@Washoe](https://boards.straightdope.com/u/Washoe)\ **Post date:** [May 8, 2005, 4:22am UTC](https://boards.straightdope.com/t/why-does-metal-react-the-way-it-does-in-a-microwave/302888/4 "2005-05-08T04:22:04Z")
> [@engineer\_comp\_geek](#): > > Steel wool and CDs (which are made of a metal foil on plastic) make for rather impressive light shows because of this. I think this has been discussed before, but memory is failing me right now. If I put on a CD light show with the family microwave, will I damage it? If so, can I do it for ‘just a coupla seconds’ and get away with it? ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [May 8, 2005, 5:19am UTC](https://boards.straightdope.com/t/why-does-metal-react-the-way-it-does-in-a-microwave/302888/5 "2005-05-08T05:19:37Z")
> [@Washoe](#): > > I think this has been discussed before, but memory is failing me right now. If I put on a CD light show with the family microwave, will I damage it? If so, can I do it for ‘just a coupla seconds’ and get away with it? It shouldn’t damage the microwave if it’s only for a few seconds, but the CD will be toast. We used to do it all the time with our work microwave when we were bored. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [May 8, 2005, 12:39pm UTC](https://boards.straightdope.com/t/why-does-metal-react-the-way-it-does-in-a-microwave/302888/6 "2005-05-08T12:39:29Z")
You probably mean, “thin metal” like metal plating. Microwaves make currents circulate in the metal which in turn generates a mirror image of the microwave outside the metal. If this works out in the simplest way, you’d say the metal is reflecting the microwave. The same thing happens with light and radiant heat and radio and so forth. If the metal is so thin that the currents overload it, then it burns up and arcs instead. Metal is generally fine in a microwave if yo take the reflections into consideration. Hell, that’s what the interior of the microwave is made of. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [May 8, 2005, 3:44pm UTC](https://boards.straightdope.com/t/why-does-metal-react-the-way-it-does-in-a-microwave/302888/7 "2005-05-08T15:44:17Z")
FWIW, in [this](http://boards.straightdope.com/sdmb/showthread.php?t=301741) thread I said: > [@Crafter\_Man](#): > > One of the biggest myths is that you shouldn’t put metal in the microwave. Hell, I do it all the time. Besides, the chamber walls are made of metal, aren’t they? > > But there are a few guidelines: > > 1. This is obvious, but you shouldn’t encase food in metal. It will reflect the microwaves and won’t get cooked. > > 2. Do not put metal pieces in the microwave that have high resistance. This would include any metal with a small cross-sectional area (e.g. foil). This is because the microwaves induce electrical currents in the metal, and too much resistance may cause the metal to overheat via I[sup]2[/sup]R. A spoon, for example, is O.K. But foil is not O.K. > > 3. Never turn on a microwave oven with nothing in it (i.e. without a load). This creates a big mismatch in the waveguide, and a lot of the energy gets reflected back to the magnetron. This is could cause the magnetron to fail.