3 ms·

I have to disagree. Any 'model' that implies that water has some resonant frequency that microwaves are specifically designed for is misleading to the point of

I have to disagree. Any 'model' that implies that water has some resonant frequency that microwaves are specifically designed for is misleading to the point of uselessness. If microwave ovens were tuned perfectly for water, then the water near the surface of foods would absorb most of the oven's energy, and not let the center of the food warm up as efficiently... essentially causing the microwave oven to heat food more like a regular oven. AFAIK, the frequency chosen for use by microwave ovens is a balance between * A desire for the EM energy to penetrate deeper into the food (per my 2nd paragraph above) * A desire for the EM energy to not interfere with licensed communications bands, in the event that the oven is "leaky". Finally: it's not very hard to explain the concept of a dipole moment, and why molecules that have one will twist in the presence of EM radiation. In fact, if you do explain this, quite often the student will come to realize that this is also true of light, which is why (A) a vintage Easy Bake Oven toy could bake a brownie with just an incandescent lightbulb, and (B) will serve to demystify microwaves as being just sub-infrared light.

delta_p_delta_x 3y ago
> A desire for the EM energy to not interfere with licensed communications bands, in the event that the oven is "leaky" I'm not sure how deep a desire this is, given microwaves operate at 2.45 GHz wideband, which is bang smack in the middle of 802.11n Wi-Fi and Bluetooth...
- tass 3y ago
  That frequency was chosen because it's not part of licensed bands, doesn't mean the band is unused. Also, microwaves have been around a lot longer than wifi and Bluetooth.
tonymet 3y ago
Then come up with a better model for chefs
- rvbissell 3y ago
  Well, I kinda did in my last paragraph. But if you want it more ELI5: "Some molecule shapes rotate like windmills when light or radio waves (same thing) pass close by them. Water happens to be one of those shapes, but there are others in food too, so it is not just about water. Also, there is nothing special about the frequency of microwaves to make this happen; microwave ovens use that frequency because it is considered a "free for all", and you don't have to ask the government for permission to use it for anything (cooking, bluetooth, or otherwise.) The frequency used for the microwaves does make some sense for use in a microwave oven, because that frequency tends to penetrate deeper into food than visible light does." That's still a model -- because everything is, the map is not the territory -- but it's close enough that I think most internet pedants won't try to refine it more.
  - tonymet 3y ago
    It doesn't explain why butter melts but shortening doesn't. sounds like you'll need a better model
    - rvbissell 3y ago
      ... because shortening isn't butter. Someone else in this thread mentioned that fats have dipole moments, but that doesn't mean that all fats react with the same intensity. For any affected substance: molecular weights, crystalline structures, etc all play a role. You aren't uniquely "ringing water's bell" with 2.45GHz

delta_p_delta_x 3y ago

> A desire for the EM energy to not interfere with licensed communications bands, in the event that the oven is "leaky" I'm not sure how deep a desire this is, given microwaves operate at 2.45 GHz wideband, which is bang smack in the middle of 802.11n Wi-Fi and Bluetooth...

tass 3y ago
That frequency was chosen because it's not part of licensed bands, doesn't mean the band is unused. Also, microwaves have been around a lot longer than wifi and Bluetooth.

tonymet 3y ago

Then come up with a better model for chefs

rvbissell 3y ago
Well, I kinda did in my last paragraph. But if you want it more ELI5: "Some molecule shapes rotate like windmills when light or radio waves (same thing) pass close by them. Water happens to be one of those shapes, but there are others in food too, so it is not just about water. Also, there is nothing special about the frequency of microwaves to make this happen; microwave ovens use that frequency because it is considered a "free for all", and you don't have to ask the government for permission to use it for anything (cooking, bluetooth, or otherwise.) The frequency used for the microwaves does make some sense for use in a microwave oven, because that frequency tends to penetrate deeper into food than visible light does." That's still a model -- because everything is, the map is not the territory -- but it's close enough that I think most internet pedants won't try to refine it more.
- tonymet 3y ago
  It doesn't explain why butter melts but shortening doesn't. sounds like you'll need a better model
  - rvbissell 3y ago
    ... because shortening isn't butter. Someone else in this thread mentioned that fats have dipole moments, but that doesn't mean that all fats react with the same intensity. For any affected substance: molecular weights, crystalline structures, etc all play a role. You aren't uniquely "ringing water's bell" with 2.45GHz