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Fri 15 Oct, 2004 02:58 pm
from Faraday's law, it seems that any metal object exposed to a magnetic field will have some proportional induced voltage and hence current...I think that microwave ovens operate by alternating the direction of a magnetic field at the frequency of microwaves (which causes torque on the polar water molecules in a substance, and this rotation would create the heat hence heating the food)...anyway, I was thinking about microwaving a light bulb to see if it turns on. I've heard that microwaving metal objects can damage the microwave...but I can't see any logical rationale to support this, my only thought as to why microwaving metal would be "bad" is that it would be inducing charge in the metal resulting in a lot of sparks and possible a fire hazard...am I right?
The danger to the oven is that the sparks can damage the metal cavity. If you severely pit the cavity, the oven will be unsafe to use.
I would not do it (on my own oven that is).
Microwave ovens operate by microwaves, which are elctromagnetic waves and hence can produce a current in a metal object just as you say. In a thin material (metal foild, metal trim on plates, sharp points of silverware) the current can produce heating. The current can also produce sparks in some cases. The right metal objects can go into a microwave (such as the metal racks contained in many of th newere ones) but those are tested before they get to the consumer to be sure they are safe. The wrong objects (thin or sharp ones) can, as you say, be a fire hazard.
As for the lightbulb, officially I don't recommend it because it could potentially be dangerous, but I have done it in an old microwave. It's actually more impressive than the light just turning on. The argon in the bulb gets ionized, creating a plasma with a purplish glow. Then the bulb explodes, flinging shards of glass.
By the way (reading the title of your post) the analytical plasma produced in essentially the same way as the one in the lightbulb is called a MIP or microwave induced plasma.
aw....I wish I hadn't posted this, it would have been so fun to have that surprise! well I definitely have to do it now.
A light bulb without a metal base would be better and clip off the wire leads as short as practical. The filliment might get hot enough to light. The argon will glow purple if the filliment is broken, and likely will glow even if the filliment is intact. Results will vary with manufacture and size of bulb. Low watts, low voltage bulbs are likely best. Try 3 seconds and let it cool 10 seconds before an other three seconds and the bulb may not shatter.
My guess is the argon does not get hot enough to burst the bulb, but failure is because the glass to metal seals gets too hot. The magnetron may overheat and fail if you put certain shapes of metal in a microwave. but the new microwaveovens are quite well protected. A grease fire on some greasy foil can do considerable damage to the interior finish. Neil
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