How does Microwave Oven WorK? (Mode of Operation Explained)

In today's article, I'll expound about something that hopefully you guys find interesting.
We use Microwave Oven every day but maybe never thought about how it works and specifically I'm going to explain how it really works down to a molecular level.

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A microwave uses microwave radiation to heat up food as you probably guessed from the name. A home microwave typically has a frequency of 2.45 gigahertz which is in the microwave electromagnetic spectrum but there are other frequencies for instance that industrial microwaves might use which are closer to around 915 megahertz. As a side note, this is kind of why microwaves can interfere with some Wi-Fi routers because 2.4 gigahertz is very close to the 2.4 gigahertz that many routers use in your home.

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Electromagnetic spectrum}

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How exactly do these microwaves heat up food?

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The first thing you need to understand is that a microwave generates an electromagnetic field at these frequencies that different molecules are going to try and line themselves up with the field. These specific types of molecules are called “Polar Molecules” and what this means is that one side of the molecule is going to be more positively charged and the other side is going to be more negatively charged. For example, water is one of these polar molecules and also a lot of fats are polar molecules as well.

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Polar molecules}

What the microwave does is it creates this EM field causing certain molecules to move and turn to try and align with this field but not only that, the microwave also alternates this EM field back and forth so molecules are going to start to churn and flip back and forth and move trying to constantly stay in line with this magnetic field. You can kind of imagine how this would start to create heat with all these molecules turning and bumping into each other.

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Electromagnetic field inside a microwave}

And as I said, the heat is not just transferred directly to the molecules that are starting to flip but they also bump into other molecules and transfer heat through conduction. That's pretty much all you need to know about exactly what the waves are doing.

There's a common misconception that microwaves heat food from the inside out, that's not true.

For uniform substances and food that are the same density and everything inside, you're pretty much going to get a uniform heating throughout the entire object or substance however, a lot of uneven heating comes from unevenness in density and substance in the food itself not just from the unevenness of the microwaves. However, that unevenness is partly contributed to uneven distribution of the magnetic waves, they're kind of going to bounce around some parts the microwave and some are going to get more hot spots than others but it's also because of different substances within the food itself and different molecules.

For example, if you have a piece of food where the outside layer is very dry but the inside is very wet and had a lot of water molecules in there, then the inside layer is going to heat up a lot more quickly because it has more molecules that are going to be more easily aligned by the magnetic field as opposed to the outer layer.

A lot of times to combat this unevenness, you'll see turntables in the microwave which kind of turns all the food around to avoid those hot spots and evenly heat the food. You might have also noticed a defrost setting on most microwaves that's also good for heating uneven foods, how that works is the microwave is going to be putting out much lower power so the hot spots aren't going to be cooked as quickly giving it more time to conductively spread heat to the cooler areas of the food that aren't being heated as quickly through the microwaves themselves.

This would be as opposed to putting it on full power where some hot spots are going to cook really quickly leaving others completely uncooked, the defrost setting can kind of make it so that the warm spots have more time to heat up the colder spots.

You might have wondered why you shouldn't put metal in the microwave.

Basically, metal objects in a microwave kind of act like an antenna and generate an electric current within that object.

This is because when any metal object is placed within any changing magnetic field, it generates an electric current within that object and since we know that the microwave is creating an alternating field, you can see how putting a metal object in the microwave is going to generate a lot of electricity current in whatever you have there.

If you have for example an object like a fork that has lots of points and stuff like that you're going to get a lot of opportunities for the electricity of bounce between each other and create sparks and arcs, superheating the air around it, so you definitely don't want to put metal in the microwave.

That's pretty some cool stuff about microwaves that you probably didn't need to know but maybe you're glad you do now. I want to know what you guys think about this, leave a reply on this post and share your thoughts.

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References: 1 - 2 - 3

Image sources: 1 - 2 - 3 - 4 - 5

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_{GIF made by @foundation}

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Thanks to @camzy & @samstickkz for this amazing toon.