Putting metal objects in the microwave can cause fire, explosion or nothing?
Microwave is one of the great inventions of the 20th century, now when using microwave ovens, manufacturers still warn that not to use metal and especially aluminum objects in the oven. microwave. If not can cause fire or explosion, but why is that, we will try to find out through the working principle of microwave ovens.
The technology used in a microwave oven is quite simple, it uses microwaves to heat food. Microwaves are generated from the magnetron emitter, are guided along the waveguide, into the cooking compartment and then reflected back and forth between the metal walls of the cooking compartment and absorbed by the food. Microwaves in a microwave oven are oscillations of an electromagnetic field with a frequency usually at 2450 MHz (wavelength 12.24 cm). Food molecules (water, fat, sugar and other organic matter) are capable of absorbing this type of wave and causing the molecules inside to vibrate. Rotational vibrations are converted into chaotic thermal motion through molecular collisions, heating the food.
Another special feature is that the molecules of glass, some special plastics or paper are difficult to heat up by microwaves at 2450 MHz. As a result, food can be stored in utensils made of the above materials in a microwave oven, with only the food being cooked. However, for metals, especially aluminum, things are different.
Although the internal structure of the microwave oven is a Faraday cage consisting of metal or metal mesh surrounding it, ensuring that the waves do not escape. The holes in this mesh are much smaller than wavelengths (12cm), so microwaves don’t get through, but light (at much shorter wavelengths) still gets through, helping to see the food inside.
Like a mirror, however, instead of reflecting light, these metal plates reflect microwaves. If you use a thick aluminum pot and place it in the microwave, the food will never be heated up because the microwaves are blocked by the pot.
That’s for thick metal objects, but with thin metal foils things get a lot worse. The electromagnetic field in the microwave creates a conduction current in the metal. For large and thick metal objects, they can withstand this conduction current without any problems. However, for thin pieces of metal, aluminum foil, they can be overwhelmed by the internal current and heat up very quickly. Therefore, it can cause fire , especially for wrinkled aluminum foil and foil, this phenomenon occurs more strongly.
Vibrations of microwaves can create a concentrated electric field at the corners or edges of a metal object, ionizing the surrounding air so you can hear crackling noises, or see sparks are a bit like lightning. However, there will be no explosion.
The truth is that your microwave can catch fire if you put a thin metal plate inside , but there will not be an explosion similar to a gas cylinder explosion. And for thick metal items, nothing will happen, only the food inside is not heated.
Many microwave ovens now have a built-in grill mode, in this mode the microwave uses heat from a resistor or halogen lamp, not using microwaves. Then the microwave oven is like a normal electric oven, so in this mode you can use the wrapping paper, the metal grid inside the microwave.
Metals aren’t the only objects that can create sparks in a microwave. There are a lot of trending videos online that show half of a grape creating a spectacular spark of plasma , Plasma is a gas of charged particles.
Many theorists have tried to find an explanation, proving that it must be related to the accumulation of electric charge as in metals. But Aaron Slepkov and his colleagues conducted scientific experiments to get to the bottom of the phenomenon.
“What we found is much more complex and interesting ,” he said.
By filling hydrogel spheres – a super absorbent polymer used in disposable diapers – with water, researchers have found that geometry is the most important factor in creating sparks. in grape-like objects. Grape-sized spheres happen to be particularly great concentrations of microwaves.
The size of the grapes caused microwave radiation to accumulate inside the grapes, eventually generating enough energy to separate electrons from the sodium or potassium inside the grapes, creating a spark that grew into a plasma.
The team repeated the experiment with quail eggs – roughly the size of a grape – first with quail eggs with the insides intact and then with quail eggs with the insides removed. The slime-filled eggs created hot spots while the empty eggs produced no reaction at all. This shows that to be able to produce a metallic-like glittering reaction, we need a chamber of water, the size of a grape.