If you're not supposed to put metal in the microwave, why are microwaves made out of metal ?

Question

what about foods that are high in metals, like vegetables that have lots of iron ?

Answer 1

This is a perfectly legitimate question and the answer lies in the reason why you are not supposed to put metal in the microwave.

Metals, especially with pointed features, acts like an antenna that will be the receptacle of microwave radiation. Any metallic conductor will have the greatest concentration of charges near the pointed features(the reason is pretty simple, if you are not sure, I can elaborate on this or you can look it up in a physics books under electrostatics). This concentration of charges causes the dielectric breakdown of air(air is a non-conductor originally). After the breakdown, the air becomes conductive thus you see the cool sparks between the fork tines.

After you understand the mechanism of why this is a no no. Let's consider the design of microwave oven. The metallic box inside the microwave is the final space microwave radiation is channeled to after going through the waveguide from the wave generator. The waveguide and the metal box are on the scale larger than the microwave radiation(typically in the range of few centimers), thus they will not be able to function as an antenna. The basic design premise of antenna is that they have to be on the the same of the wavelength of the targeted radiation. This is why fork tines, on the scale of centimeters, exhibit the antenna behavior. On the side note, this is also why the metal screen you seen works because it is on the scale of millimeter and prevents microwave radiation from leaking out.

Thus, the metal the microwave is made out of does not pose as a problem; in contrast with metallic items you put in that happen to be in the same wavelength scale of the microwave radiation itself.

In addition, food with metallic content has the metal in tiny tiny scale that won't function as an antenna.

Answer 2

Microwaves are reflected by metal and generate into the metal electrical currents that spark to the interenal casing.
The internal casing itself is connected to the ground.
If the mw case is not made in metal the microwaves will leak outside !
Putting metal into the microwave can also damage permanently the magnetron of the mw.

Metal in the vegetables is so scarce, but so scarce that you can consider it 0 respect the mass of the vegetable itself. And also in the food there is water and polar molecules that can absorb the mw (and cook the food)

if you want to put a cd as suggested by the post before mine, put also a glass full of water, to absorb the mw and you will not damage the magnetron, but do it only for a few seconds.
LCD displays, soap, marshmallow, and eggs (watch out for the explosion) are cool to see into the micro.

Answer 3

The metal in the inner-part of the microwave is special so that it doesn't spark.

If you put metal in the microwave-- even tinfoil, it sparks and/or catches on fire.

I found this out by accidently microwaving a hamburger in its wrapper (the wrapper was made of some sort of metal, probably tin foil).

Since the microwave itself is safe, the metal used in that will not catch on fire or spark. Any other metal placed inside will though. That is why the microwave can be made of metal.

Answer 4

its the inside of a microwave that reacts to metal objects when the microWAVES are heating your food it conducts through the metal causing a reaction similar to trees hitting power lines

Answer 5

Hmm....what a good question. Only thing I can think of is the inside must be painted with a special paint that deflects the microwaves.

Answer 6

the zap is in the middle of the microwave. Have you ever had food in the wave that is hot in the middle only?

Answer 7

its the centre of the microwave that gets the zap, and the casing is grounded to earth

Answer 8

put a cd in it it looks cool

Answer 9

I honestly don't know..But its a good question...