ELI5: how microwaves work where some types of containers that hold the objects inside will not be as affected by the microwave while others will be extremely hot to touch?
ELI5: how microwaves work where some types of containers that hold the objects inside will not be as affected by the microwave while others will be extremely hot to touch?
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The temperature comes from molecules vibrating. It turns out that microwave radiation is resonant with the frequency of the water molecules vibrating, so the microwave appliance producing the microwave radiation will tend to heat up the water in the food much faster than it could heat up a ceramic plate or glass container or the like.
Also, the microwave appliance will produce standing waves – these are waves where the electromagnetic field will oscillate a lot around certain points and very little around other points. (Like the waves on a plucked string or a drum.) This means certain parts of the microwave appliance will not absorb much microwave radiation, and will not get hot. Having a rotating base somewhat offsets that, as the food is going through different parts of the highs and lows. Additionally, this is why some food needs to sit for minutes after being microwaved, so the heat can redistribute itself through conduction.
Basically it depends on how much water or air is in the material the container is made from. Microwaves work by using micro radio waves (thus the name) to cause the water and/or air molecules in the food to move around and therefor heat up. The same thing can happen with the container if it has the right composition
Microwaves work by a special type of light (a microwave) hitting the water molecules in your food and making them vibrate. Containers that aren’t affected by this basically act like windows to the microwaves allowing them to pass through unaffected while other materials are more like walls and instead absorb the microwaves
Microwaves work by dielectric heating. Dielectric heating is when the polarity of a molecule aligns itself in an electromagnetic field and as that undergoes changes the molecule rapidly moves heating up in the process. Not all molecules are vulnerable to this kind of heating and some like ice are resistant to it. https://youtu.be/V0dtq3rCEjw
Some bowls, like ceramics, can get water inside of them, especially if they have an unfinished edge, like most do on the bottom. These can explode in a microwave, so if you notice ceramic plate/bowl is super hot, it has water in it and is compromised, don’t microwave it anymore.
Glass is the ideal heating surface.