Why do metal objects behave violently in microwave radiation?

In summary: It's an amazing process and I'm really looking forward to trying it myself!In summary, microwaves are just powerful radio waves, and when there is metal around it acts like an antenna. This causes sparks in the air depending on the shape and position of the metal in the oven. The theme even matches!
  • #1
misskitty
737
0
I'm not really sure where this question goes. I was wondering why metal behaves so violently when exposed to microwave radiation. For example if you put a metal object into a microwave, it sparks and if there are things attached such as plastic tops will explode off of what ever is in it. What is it about the metal which causes this to happen?

~Kitty
 
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  • #2
It is because metals are good conductors. The dissipated heat is roughly proportional to the substance conductivity, so metals can be easily heated to very high temperatures. Sparks are actually the discharges from the metal edges, because the electric field tends to concentrate in such places.
 
  • #3
Specifically, metals have a large number of "free" electrons which repsond to the fields of the microwave radiation. It is the collective agitation of this large number of free electrons that makes metals do interesting things in microwave ovens.
 
  • #4
I was very surprised to see that the instruction manual for my brand-new oven says that you can put metal in it as long as it's kept away from the edges! There must be some modification from the original designs to allow that.
 
  • #5
misskitty said:
I'm not really sure where this question goes. I was wondering why metal behaves so violently when exposed to microwave radiation. For example if you put a metal object into a microwave, it sparks and if there are things attached such as plastic tops will explode off of what ever is in it. What is it about the metal which causes this to happen?

~Kitty

Microwaves are just powerful radio waves. When there is metal around,
it acts like an antenna. The antennas in your radio generate a few
milivolts from the radio stations nearby.

But when the "antenna" (a spoon) is in a microwave, it's like being right up
against a powerful transmitting tower. The voltages become high enough to
cause sparks in the air depending on the shape and position of the metal in
the oven.
 
  • #6
On an only slightly related topic, CD's don't do very well in the microwave, either. It does turn them into interesting desk coasters, though. The theme even matches.
 
  • #7
Danger said:
I was very surprised to see that the instruction manual for my brand-new oven says that you can put metal in it as long as it's kept away from the edges! There must be some modification from the original designs to allow that.

That depends. Metal was never bad for the microwave itself so long as the arcs didn't damage the walls or door. You don't get any more reflected power with metals in the machine than you do running it empty, and reflected power is really about the only thing that damages magnatrons other than physically abusing them.

Maybe you are dealing with something new? To tell, I think it best to see what happens when you put metal objects inside. :biggrin:

As an interesting side note, I had the pleasure of having dinner with a couple of gentlemen from Lambda Technologies recently. They do most of their business curing glue on semiconductors. They use a special technique involving quickly altering the frequency of microwaves that prevents arcing entirely.
 

1. What is the relationship between metal and microwave radiation?

The relationship between metal and microwave radiation is complex and multifaceted. Metal is a good conductor of electricity, and this property makes it able to reflect and absorb microwave radiation. When exposed to microwave radiation, metal can heat up quickly and become a potential fire hazard. However, metal can also be used to shield against microwave radiation, as it can block the waves from penetrating through.

2. Can metal objects be safely used in a microwave?

It is generally not safe to use metal objects in a microwave. As mentioned before, metal is a good conductor of electricity and can cause sparks and potential fire hazards when exposed to microwave radiation. Additionally, metal objects can also disrupt the distribution of microwaves, leading to uneven heating and potential damage to the microwave itself. It is best to avoid putting any metal objects in a microwave.

3. How does metal affect the cooking process in a microwave?

Metal can greatly affect the cooking process in a microwave. As a good conductor of electricity, metal can reflect and absorb microwave radiation, causing uneven heating or even sparking. This can result in food not being fully cooked or even causing a fire. It is important to avoid using metal containers or utensils in a microwave to ensure proper and safe cooking.

4. What types of metal are safe to use in a microwave?

Generally, it is best to avoid using any type of metal in a microwave. However, some microwave-safe metal cookware, such as aluminum foil or metal baking pans with no sharp edges, may be used in a microwave if they are labeled as such. It is important to always follow the manufacturer's instructions and to never use any type of metal containers or utensils that are not specifically labeled as microwave-safe.

5. Can microwave radiation affect the properties of metal?

Yes, microwave radiation can affect the properties of metal. When exposed to high levels of radiation, metal can become heated and even melted. This can cause changes in the metal's structure and properties, such as weakening its strength or altering its electrical conductivity. It is important to avoid exposing metal to high levels of microwave radiation to prevent any potential damage or alteration of its properties.

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