Apparently if you run a microwave when nothing is in it, you destroy your microwave.
Why does this happen?
-Kris
All that energy has to go somewhere, so if there’s no food it will heat up various parts of the microwave.
If I might put it another way, since I’m curious. Suppose you put a very small piece of food in the microwave. How come all the waves go into the food and do not damage the oven itself, less of course than if it was completely empty, but damage it nonetheless?
Run it long enough and the microwave will be damaged, and the food will be toast. And it seems to me people overestimate the damage microwaves do to themselves. I’ve run many of them for upwards of a few minutes when they were empty (this was before I realized most of them have ‘kitchen timer’ modes,) and they all were fine afterwards.
Modern microwaves don’t suffer all that much even from fairly extensive empty running. It used to be a problem with older microwave ovens back when the magnetron tubes were constructed with a glass envelope. The reflected microwave energy ultimated wound up heating the magnetron, and eventually the glass would fail, a leak would develop and the tube would cease emitting. Nowadays, the magnetrons are made with ceramic envelopes and can withstand a great deal of heating without failure. You can generally run a modern oven for a fairly long time empty with no problems, but as with all things, it is possible to overdo it. Even a tough ceramic magnetron has its limits, so don’t be surprised if you leave your oven running empty for an hour or so and your next cup of coffee comes out cold.
I’ll add that the energy is specifically designed to be absorbed by objects that are partly made up of water, which covers most food products you’d put into a microwave. The parts of the microwave themselves do not contain water, so as long as there’s something with water inside, the waves will be most easily absorbed by that.
Also fats and sugars.
Actually my cup of coffee (not the coffee itself) comes out cold every time because the ceramic doesn’t absorb the microwaves (or at least none that are detectable as heat after the fact). If the magnetron is made out of ceramic, isn’t it as transparent to microwaves as my coffee cup?
I’m just baffled at the notion of an oven that is made out of the same stuff that it cooks. Perhaps we were that limited in the 1970’s, but in the 21st century?
Microwaves, which are radio waves, are reflected by metal surfaces like the interior walls of a microwave oven. They bounce around until they hit something that absorbs their energy.
Even fairly transparent materials absorb some of the energy, converting it to heat. Put your empty and dry coffee cup in the oven and run it for, say, 5-10 minutes. Stop the oven and check the cup temperature every couple minutes, preferably with something like an IR thermometer; your fingers will do in a pinch, but be cautious–some ceramic items heat up much more than others, particularly those which are older and well-used. You’ll still see it heat up, despite being relatively MW transparent.
If you’re saying the frequency of 2.45 GHz was chosen because it is a “resonant frequency” of the water molecule (as many believe), you would be incorrect.
I tried blowing a microwave up, I had it setup outside and put in man different types of metal objects, cds, guitar strings, forks, tin foil .ect and i couldn’t get the thing to blow up. Hell i even made a fire in there. And nothing.
Also I remember a time when a friend put a the microwave on for 1hour 30min in his student housing to see what would happened, the thing got really hot inside by the end. the glass plate shatted but the thing still worked!
Well, the very first microwave ovens were made out of buttered mashed potatoes and string beans.
So you see we’ve come a long way, actually.
I have a 1987 (!) 1kw model I got for free.
Any ballpark idea how long it would take to damage the oven by running it empty?
I occasionally heat up hot dogs one at a time in the oven, and I noticed the microwave instructions on the package say to put a half-full cup of water in with the dog. I assume this is to absorb excess microwaves. But I’ve never done this. The heating takes 1 minute or less, and I interrupt the heating half way through to rotate the plate. Am I damaging the magnetron? Is the damage cumulative, i.e. will it completely fail one day or gradually lose power?
It is sinful. Nothing, as we know, is sacred. Microwaving a sacred thing is heresy. :eek:
I never heard of putting a cup of water in there. I always wrapped my weiners in a very wet paper towel to cook or probably steam them is more exact.
As for another question, how about heating potatoes? I’ve seen microwaveable potatoes for $1.50 at the supermarket, but neither I or my father have had any difficulty in heating and baking regular potatoes in 20 years.
Might be nice if you explained what is correct, rather than just contradicting people.
You are right, however; it’s not a resonance principle. Rather, microwave ovens work by dielectric heating. The dipole in water molecules (and to a lesser extent, fats and other molecules) attempts to align itself with the rapidly alternating electromagnetic field of the microwaves. This rotation is what causes the temperature to rise. The heating of water works so well because it has a relatively strong dipole, not because 2.4GHz has any particular resonant significance.
It’s also why microwaves are much worse at defrosting things than they are at cooking them; the water molecules in ice have far less freedom to move, so the heating works less well. This in turn is why you tend to end up with one bit getting cooked while the rest remains frozen. As soon as one bit’s defrosted, it heats far more efficiently, and thus cooks preferentially to the frozen remainder.