If you put metal in a microwave you get arcs, so you’re cautioned against doing that. But my microwave has a metal rack midway between the floor & ceiling. Why doesn’t it arc?
See here for the answer to that question. 
Arcs only occur when you get large potential differences across a sufficiently small airgap. Also, arcs are more likely to occur at sharp points - smooth, rounded parts tend to exhibit less arcing. Evidently, this rack is designed so as to avoid these conditions.
That page made my Firefox freeze up like a deer in headlights.
Beakman (From Beakman’s World) once safely put a fork in the microwave. The trick was to be sure it wasn’t touching the sides or bottom. He put it on top of a plastic bowl or something so that it was suspended in the middle of the microwave.
Put a bag of microwave popcorn on the turntable under your metal rack. Let the popcorn pop until it raises the rack and shifts it from the plastic hooks it sits in. Then take the rack and popcorn out of the microwave and try to remove the scorch marks from the sides of the oven.
From this “experiment” I performed a few years ago :smack: I concluded that the rack will not arc as long as it is in its correct position. Move the rack, and watch the arcs begin.
Funny. Works fine on Windows98. Usually it’s the other way around!
My copy displays it OK, sans a missing plugin, which turns out to be Apple Quicktime. It would appear that you have the plugin, and your browser is valiantly attempting to play Debussy as a background.
I think that’s it, too. I hate Quicktime with a passion.
I regularly put silverware in the microwave. If I’m heating up a bowl of something, and occasionally take it out to stir it, I just leave the spoon in while it’s heating instead of finding a place to set a messy spoon on my countertop. Never had a problem.
And contrary to what’s widely believed, even if you get arcs from metal, it doesn’t hurt the microwave (unless, like in Cheesesteak’s case, it makes marks on the sides).
From the link given by silenus
In the case of the OP’s microwave, the rack midway between the floor and ceiling is included and is a part of the “cavity” and is tuned to the frequency and so no sparks. This is further proven by what Cheesesteak has experimented. If the rack is moved from its location, the “tuning” is lost causing sparks.
From the link from silenus:
and then
Any day now, we should see those answers.
Agree.
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:
-
This is obvious, but you shouldn’t encase food in metal. It will reflect the microwaves and won’t get cooked.
-
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.
-
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.
From the link given by silenus
I don’t think this is right. For one, all microwaves operate at the exact same frequency, so wouldn’t they all have similar dimensions if it were true? For another thing, the way it’s worded tells me that the person has no idea what he’s talking about. “Proportioned with the energy output from the magnetron tube”??? What the hell does that mean? The microwave designer wants it not to act as a resonant chamber, and puts a spinning metal “stirrer” in there to make sure it doesn’t.
I agree. I think this page has a better explanation.
Withing reason, it doesn’t matter how much arcing occurs in the chamber. The difficult comes from reflecting microwaves back into the output of the power tube - magnetron, klystron or whatever. Such devices are specified with a maximum standing wave allowed in the output so as not to damage the device.
So the chamber with all of its metal parts is constructed and the power tube output is located in the chamber so as to keep the standing waves in the tube output at a safe level.
Things that absorb energy, like food, don’t cause any problems because they don’t increase the standing waves in the tube output. However metal things reflect energy which changes the distribution of energy in the chamber so as to possibly increase the standing wave in the tube. Metal objects in the chamber won’t always cause power tube damage but there is the strong possibility that they will do so and therfore should be avoided.
I’m not a microwave engineer, but I guess I disagree with some of this.
First of all, I’m pretty sure that putting food (or whatever) in the microwave will reduce the SWR. The energy has to go somewhere, and if food is absorbing the energy, then I figure the SWR must decrease (which is a good thing). A good analogy is a coax cable terminated with a short vs. a coax cable terminated with a resistor. The short represents a microwave with nothing in it, and the resistor represents food. The SWR with the resistor will be less than the SWR with the short.
With the above comments in mind, I do not believe putting metal in the microwave will hurt anything as long as:
- There’s also a load (e.g. food) in the chamber.
- The metal does not have high resistance (else the metal could overheat).
Am I writing this in Sanskrit or some other obscure tongue? What is the essential difference between the sentences in bold above?