A microwave works by sending an electromagnetic waves careening through its inner cavity. These waves are calibrated to excite water molecules, causing them to jiggle around heat up the food they're in. This is why microwaves work well on soup and not so well on ancient, dessicated bread. The water in a foodstuff or small dog heats up. Although the electromagnetic waves in microwaves don't have much of an effect on any organic molecules, but all electromagnetic waves have an effect on metal.
The outer electrons on a piece of metal are relatively free from the yolk of their respective atoms, and can wander around. Water molecules do this by acting like tiny magnets each molecule has a slight negative charge on its oxygen atom and positive charge on its hydrogen atoms. As the microwave beams zip back and forth in the oven, they attract the water molecules, tugging them and forcing them to vibrate very quickly.
This vibration gets turned into heat, warming up your meal. But what about metals? Well, at a microscopic level most metals are lattice arrangements of atoms with a bunch of electrons freely floating around between them.
The microwave radiation will attract all these electrons as it bounces around inside your microwave oven, pulling them back and forth, and this generates heat inside the metal. A large sheet of very thin metal, like a big piece of aluminum foil, can in fact heat up extremely rapidly, becoming so hot that it could start to burn the microwave.
But the real danger comes from having metal with kinks or dead ends in it. This can create concentrated spots of negative charge. Electrons will naturally be repelled from areas where there is too much charge.
If these negative spots happen to find themselves in a place where they are near air, like in the tines of a fork or a kink in crumpled aluminum foil, the electrons will jump away, creating a spark and ionizing the air molecules into a plasma. It is important that in all cases when sparks are sighted inside your appliance, that the device is stopped, and the power is turned off.
This will prevent further damage and help to prevent a fire breaking out. In most cases where sparks appear in the appliance, it is likely because you have accidentally left a piece of metal in the microwave.
When the appliance is working, this will cause sparks to fly, and the metal should be taken out as soon as possible. If removed quickly enough this can usually prevent damage such as holes being burnt into the walls. However, it is a good idea to get your appliance checked by a professional microwave repair technician before using it again.
Other metals that can cause issues in your microwave are foil or crockery items with metal trim — both of which should be avoided. In rare cases, if the microwave oven receives a lot of use, or is bashed or knocked, the waveguide cover — which allows energy waves to cook through your food — in the device may become loose. In addition, if food explodes inside the machine, something can become trapped under this cover and get into the inner workings of the microwave.
If this happens, then sparks can occur, and this should be looked at by a repair professional who can get the device running again, while keeping your home safe. A microwave diode is an essential part of your device and is used for generating, mixing, detecting and switching your microwave signals.
As they are heavily used, they can occasionally be worn down or split in two. This can then cause sparks, and if the diode has shorted, it will be accompanied by symptoms such as a loud humming. There can also be visual signs and a burning smell if a microwave has a faulty diode. If either of these issues occur with your appliance, then it means that a microwave diode will need to be replaced by a professional.
For more information on how to keep your machine running correctly, you may want to refer to our article on how microwaves work. I have a Bosch microwave with an oven element under the turntable. That's why "if you take aluminum foil and put it in a flat circle, it might not spark at all," Slepkov said.
While these sparks have the potential to cause harm to the microwave oven, any food should be perfectly fine to eat afterward just in case you really did forget that spoon in your oatmeal , according to an article from Mental Floss. Metals are not the only objects that can generate a light show in a microwave.
Viral internet videos have also shown halved grapes producing spectacular sparks of plasma, a gas of charged particles. Various sleuths had searched for an explanation, suggesting that it had to do with a buildup of electric charge like in a metal. But Slepkov and his colleagues conducted scientific tests to get to the bottom of the phenomenon.
By filling hydrogel spheres — a superabsorbent polymer used in disposable diapers — with water, the researchers learned that geometry was the most important factor in generating sparks in grape-like objects. Grape-size spheres just happened to be particularly excellent concentrators of microwaves, Slepkov said. The grapes' size caused the microwave radiation to amass inside the tiny fruits, eventually resulting in enough energy to rip an electron from sodium or potassium inside the grape, he added, creating a spark that grew into a plasma.
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