Microwaves have been around for longer than most of us have been alive. These amazing little appliances have made heating up food far faster and easier than it ever was before, but for the most part, they just do their jobs unappreciated and little understood by the average consumer.

Actually, it is worse than just being little understood. Most people have an actively incorrect understanding of how microwaves work.

One of the most common myths about microwaves is that the microwaves that are generated by the appliance are specifically tuned to heat up water. This is an at least somewhat believable myth because the appliance is quite good at heating water, but not because it is tuned for this exact task. Here is an explanation for how Microwaves heat things from the US FDA:

“Microwaves are produced inside the oven by an electron tube called a magnetron. The microwaves are reflected within the metal interior of the oven where they are absorbed by food. Microwaves cause water molecules in food to vibrate, producing heat that cooks the food. That’s why foods that are high in water content, like fresh vegetables, can be cooked more quickly than other foods.”

The fact that most foods in microwaves are heated in large part because of their water content does not mean that the microwaves are tuned to heat water. Ron Schmitt is the former Director of Electrical Engineering at Sensor Research and Development Corp. In a book entitled, “Electromagnetics” he explains this exact myth:

“In reality, this myth is just that, a myth. [T]here is no resonance of water at this frequency. The first resonant peak occurs above 1 THz, and the highest loss occurs well into the infrared. There is no special significance of 2.45 GHz, except that it is allocated by the FCC as being allowable for microwave oven usage.”

In general, most solids are good vibrators because they have tightly bound atoms that can vibrate around and generate heat much more easily than a liquid or a gas. Microwaves send a fairly broad electromagnetic wave that can heat many different types of materials, including water through a process known as dielectric heating. In a blog post, Dr. Christopher S. Baird, an Associate Professor of Physics at West Texas A&M University, explained what this is:

“In dielectric heating, the electric field in the electromagnetic wave exerts a force on the molecules in the food, causing them to rotate in order to align with the field. Because of this rotating motion, the molecules collide into each other and convert their somewhat ordered rotational motion into disordered motion, which we macroscopically call heat. Many types of molecules in the food absorb energy from the microwaves in this way, and not just water molecules.”

Almost all microwaves operate at 2.45 GHz, which is a good option since it can heat all sorts of different things, including most types of foods, which they are designed for. This includes water, protein, fats, and more. In addition, this frequency of microwave can penetrate deep into foods to the point where it can heat it all the way through rather than just the surface.

Another benefit to this frequency is that it bounces off of the walls in the microwave quite easily, making the appliance heat more evenly and efficiently.

So, while it is true that microwaves can heat water very effectively, it is a myth that they are tuned to a frequency specifically chosen for its ability to heat water alone.

The more you know.

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