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ProveISaidIt t1_j2bwnfi wrote

Microwaves heat food by causing the water molecules in the food to become excited, thus banging into each other. That creates friction, which creates heat.

Objects heat up through the input of energy. Heat doesn't absorb cold, rather cold absorbs heat. Plates are typically made of some kind of stoneware, e.g. ceramic, which is clay.

Side note: Corelle dishes manufactured by Corning are glass and do not heat up on the microwave. I use Corelle for this reason.

The cold stoneware absorbs heat energy from the food. Because the food is losing heat to the plate it remains cooler. The water molecules continue to produce heat through friction that the plate continues to absorb.

I would imagine if the food were heated long enough to the point all of the water had evaporated the plate and the food would reach equilibrium. However, the food would long since become inedible if not combusted.

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Fred2718 t1_j2c8smr wrote

"it remains cooler" Lol wut? It's basic thermodynamics that something cool cannot transfer heat energy to something warm.

Dishware gets hot, even more than the food, if the ceramic or glaze contains metal elements, which can absorb microwave energy. Products marked "microwave safe" do not - they are transparent to microwaves. Clear glass is almost always non-absorbing, but many glass items cannot stand the heat from the Hot food.( More precisely, they cannot stand the stresses from uneven heating and cooling.)

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ProveISaidIt t1_j2c9rxx wrote

Which part? Microwaves heat food by causing the water molecules to vibrate.

An ice cube cools your drink by absorbing the heat from the beverage. Likewise, the plate being colder, absorbs the heat from the food that is generated by the vibrating water molecules.

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Fred2718 t1_j2cbvw5 wrote

  1. The cold plate cannot get hotter than the food by conduction of Heat from the food.

  2. Microwave energy can be absorbed (and converted to heat) by conductive/resistive structures in metal-based ceramics, as well as water molecules in food. I should add that most ceramics suck at conducting heat, so the dish's internal heat tends to stay there.

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ProveISaidIt t1_j2ccbhp wrote

I just figured out what you meant. That makes sense. I do know that when I heat food on a Corelle plate I can take the plate from the microwave and it does not burn my hand. The food is hot and I can eat from the same plate.

When using the stoneware the plate is too hot to handle but the food is not up to temperature.

I had assumed it was drawing heat solely from the food. I have always heard you cannot put a dry plate into a microwave because there needs to be water to absorb the energy.

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ProveISaidIt t1_j2dvvkx wrote

No one said something cool can transfer heat to something hot. Cold absorbs heat.

I said as the food warms from the microwaves that heat transfers into the plate. I don't know about ceramics containing metal elements or not.

I do know that Corning Corelle is made from dufferent types of glass, as explained in the link. I have been using Corelle in microwave ovens for almost 40 years and it does not get hot the way a stoneware dish does.

I can only speak from my own experience. If I want to preheat a Corelle plate I have to put water on it as the water transfers heat into it.

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jerrycotton OP t1_j2bwy5d wrote

This is the most poignant reply I have received on all my time on this website, thank you and also for the Corelle dishes recommendation.

Edit: Is this an undercover advertisement for Corelle dishes, if so you deserve a raise!! Haha

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ProveISaidIt t1_j2bxnpl wrote

LOL. No. My folks bought Corelle in the 70s when it was first introduced. When I got married I bought it for my household. So I guess that after almost 50 years that kind of makes me an expert.

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SofaKingI t1_j2cw4gl wrote

FYI that comment is full of inaccuracies.

Molecules moving doesn't cause friction, which creates heat and increases temperature . The vibration of molecules IS temperature.

Heat transfer also only works from the hotter object to the colder one. Once the plate is hotter than the food, heat transfer can't possibly be occuring from the food to the plate. It's the other way around.

So the reason the plate is so hot can't possibly be that it's taking heat directly from the food. The plate's material is absorbing the microwaves.

That last paragraph doesn't even make sense.

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epelle9 t1_j2ct8we wrote

This is completely incorrect, heat transfers from the gotten object into the colder one, if the food is colder than the plate then the plate will warm up the food, not the other way around. This is the basis of thermodynamics.

What's happening is that the plate that heats up will have a resonating frequency close enough to the microwave frequency to the point where the microwaves can be picked up by the plate instead of the water inside the food.

So the plate gets heated up instead

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ProveISaidIt t1_j2dpc7e wrote

Microwave ovens work by causing the water molecules in the food to vibrate. That's how it heats food. You can look it up.

By your explanation a dry plate with no food on it would heat in a microwave.

From what I've always heard that would damage the microwave as there has to be water to absorb the microwave energy.

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epelle9 t1_j2eipdo wrote

Yes, it causes the water molecules in the food to vibrate, but if the plate has a similar frequency to the water molecules, then the plate can heat up too.

And yes, if you have a plate that generally heats up more than the food, you can put it in the microwave and it will heat up.

Why are you arguing instead of listening? I have a major in physics engineering, I know what I'm talking about. Your explanation literally violated one of the basic thermodynamic laws.

Seems like Dunning Krueger effect in action.

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ProveISaidIt t1_j2emh70 wrote

Trying to understand a concept isn't the and as arguing. Also, you may have lead with the major in physics.

As stated, I only draw from my experience. That is articles I've read and videos from SciShow and the like.

If I hold a metal rod with a metal pair of pliers and heat the far end of the rod, the piers will heat up from hear transfer.

That's about as far as my understanding of thermodynamics goes.

I have never heard of plates having resonant frequencies as microwaves. That, however, does not mean it's not true, only that I have more to learn.

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ProveISaidIt t1_j2ew3y6 wrote

I took a look at the first law of thermodynamics. Way too complicated for a quick read. I wasn't a science major.

It talks about energy in a closed system. Isnt the microwave inputting additional energy while it is running?

If you don't mind educating me a bit by continuing the dialog. I find science fascinating. Sadly, I didn't get the science gene. My dad was a chemist, one brother a biochemist, the other brother was mechanically minded. Even my daughter and niece are in the sciences.

I read articles, watch videos and grasp at concepts.

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epelle9 t1_j2ftj0f wrote

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.

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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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