epelle9 t1_j2ftj0f wrote
Reply to comment by ProveISaidIt in ELI5: Why plates get too hot to touch in the mircrowave but the food can still be cold? by jerrycotton
Well, it's actually the second law that states this, not the first one. It says that heat flows from the object with higher temperature to the object with lower temperature.
How a microwave basically works is that it sends out microwaves at a certain frequency that they interact with water.
It basically interacts with most polar molecules causing them to spin and heat up. Since water is a polar molecule that can interact with microwave frequencies, it interacts with them, absorbing the wave and as a result producing heat. Transforming the electromagnetic energy (since microwaves are electromagnetic waves) into thermal energy.
But water isn't the only polar molecule that can interact with microwave frequencies of electromagnetic waves, other molecules can have that same interaction too.
So when you put a plate (or any object) into the microwave that also has molecules that interact with microwave frequencies, that plate (or those objects) also heat up just like water would.
If you want to know what causes the molecules to spin, it's that their polarity (which is linked to its dipole moment) wants to align with electromagnetic fields, and the microwaves (as well as any electromagnetic wave), is just a disruption to the magnetic field, so the polar molecules wants to align with the constantly changing electromagnetic field.
Water (H2O) is a polar molecule because of it's structure, since the molecule is formed at an angle, with the O molecules going the opposite side as the H molecule, since O is more electronegative, it attracts the electrons to one side, causing that side to have more negative charge and the other side a positive one.
Think of it as every water molecule being a compass, with one side negatively charged and the other positively. It wants to align with the world's electromagnetic field and point north. Now if you bombard the world with other electromagnetic waves, the field will be constantly changing and causing the compass to spin fast, which would cause friction that ends up being heat.
But it would heat up all compasses, not just the ones created from X material. And there are many molecules that are polar, not just water.
ProveISaidIt t1_j2fuy7h wrote
Thank you. I had heard microwave was discovered because it melted a chocolate bar in some guys pocket. I knew that you can use them to ionize the gas in florescent tubes and freak out the Boatswains Mates or so I'd heard. I was in the US Navy Reserve for a spell.
I didn't know things like dishware would heat up on its own. We got our first microwave 40 years ago as mentioned. The warning was always never to run the oven without something moist to absorb the energy. So I've never put just a plate in.
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