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Microwave Sparking

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Garth Vader

Garth Vader

Student
May 30, 2022
2
Hello,

I am curious as to why a microwave doesn't spark even though it has a metal turn tray but it does spark if any other metal is put in.

Thank you,
Garth
 
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The interior of a microwave is full of a high energy EM field, distortions of the field caused by conductive objects such as even grapes can cause arcing and plasma generation

see


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Grapes are neat in a microwave...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik
 
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I wonder what would happen if you stuffed a marshmallow with a grape and then microwaved it....
 
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Best way to clean a microwave oven - put in a raw egg and cook on high for 3 minutes. Then clean all the interior surfaces to remove the egg.

Sparks depend on differential potential - when there are two pieces of metal they each take on the average of the EM field inside the oven; since that field isn't uniform the voltage won't be the same and sparks can happen if the gap is smaller.

There are some experiments with neon bulbs at different locations in a microwave oven showing the lack of uniformity.
 
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A company I worked for started a Quality initiative, and as part of the effort, gave everyone a new coffee mug with the logo in goldish foil. The email sent out the next day instructed everyone not to use the cups in the microwave ovens...due to a small fire started by one of the engineers...
 
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I wonder how many dishwasher cycles it took before that gold leaf was gone?
 
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The walls of the oven are metal to reflect and contain the microwaves (Faraday cage). Conductors reflect electromagnetic radiation because an electric field induces eddy currents that create an opposing electric field that appears as reflection (acting like an antenna). If the metal is only a thin foil, these eddy currents can cause heating and sparking. If two metal objects in the oven touch, there will be sparking at the contact point. It is an over-simplification to say that you cannot put metal objects in a microwave oven. I leave spoon and forks in bowls that I am reheating, with no problems.
 
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Foil tends to have sharp edges and points, which can increase the local field strength. The guy on Electroboom as tried all sorts of utensils in a microwave with no zapping, but he did fry an LED

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