It may have happened to you sometime. You leave the mug in the microwave half asleep and you forget to remove the spoon from it. You give it to heat and suddenly they start to emergemini fireworksin the kitchen. Oh no! The spoon! It’s too late…
Although putting a spoon in the microwave or any other metallic thing in the microwave is not necessarily dangerous, why does metal generate sparks in there?
The microwave oven is based on a device called a magnetron, a vacuum tube through which a magnetic field is made to flow. The device spins electrons and produces electromagnetic waves with a frequency of 2.5 gigahertz (or 2.5 billion times per second). For each material, there are particular frequencies at which it absorbs light particularly well, and it turns out that this 2.5 gigahertz is a frequency for heating water – although not the most efficient one. Since most of the things we eat are filled with water, those foods absorb microwave energy and heat up.
When microwaves interact with a metallic material, electrons on the surface of the material spill out; this does not cause a problem if the metal is smooth all over. But where there is an edge, such as the tines of a fork, charges can build up and result in a high concentration of voltage.And with that they could cause an explosion …
Ionized particles absorb microwaves more powerfully than water,so once a spark appears, more microwaves are absorbed, ionizing even more molecules so that the spark grows like a fireball (which could happen with a fork or a metal object with rough edges).
While these sparks have the potential to cause microwave oven damage, any food should be perfectly fine to eat even after the metal item is forgotten in the microwave … (although you are unlikely to feel like it).
Other objects that can cause sparks
Metals are not the only objects that can generate sparks in a microwave. Grapes cut in half, for example, produce spectacular sparks of plasma, a gas of charged particles. How is this?
A study published in the journal Proceedings of the National Academy of Sciences exposed a similar experiment to test the effect of grapes in microwaves – which are often the subject of multiple viral videos on the Internet. By filling spheres of hydrogel, a super absorbent polymer used in disposable diapers, with water, the researchers found that geometry was the most important factor in generating sparks in grape-like objects. The grape-sized spheres turned out to be particularly excellent microwave concentrators.
The size of the grapes caused microwave radiation to build up inside the tiny fruits, eventually resulting in enough energy to extract an electron from the sodium or potassium inside the grape, he added, creating a spark that turned into plasma. .
The experts repeated the experiment with quail eggs , which are roughly the same size as grapes, first with their natural yellow insides and then with the drained liquid. Eggs filled with substance generated hot spots, while empty ones did not , indicating that mimicking the show of metal sparks required an aqueous chamber the size of a grape.
So remember:
Electromagnetic waves, such as those emitted in a microwave oven, cannot penetrate metals, instead inducing surface electrical currents in the metal. Where there is a bend in the metal, the electromagnetic fields are concentrated, and the sharper the bend, the more the electromagnetic fields contract. With very sharp corners, like the edges of aluminum foil or the aforementioned fork, the fields can become so concentrated that they are strong enough to remove electrons from air molecules. This ionization of the air is the spark you see in a microwave.
