Microwaves on one of the longest (and lowest energy) waves in the entire spectrum, and yet we use these waves to cook food. Since X-Rays, Gamme Rays, and UV Rays are much more powerful (they are very short and highest energy waves on the spectrum), does this mean they would be able to cook food, such as potatoes, faster? Since you are adding more energy to the object, wouldn’t this mean it would obtain the energy it needs to be cooked faster? And if so, why don’t we use faster waves to cook food? Is it because of the higher levels of radiation?
I need to know the answers to every question I think of, and when my chemistry teacher doesn’t know it gets me very frustrated! Please help me out!
Yes, you probably could cook with X-rays. Early X-ray machines sometimes did just that to patients. IANAP, but I think the problem would be with shielding. Microwaves are stopped by the thin metal walls, and the metal mesh screen in the door. An X-ray cooker would probably have very heavy thick lead walls.
Well, visible light is shorter than microwaves. Try that and see if shining a flashlight on your soup heats it up. Microwave ovens emit light in a frequency that is exactly right to excite water molecules, causing them to warm up. I can’t explain any more than that, because I’m a student of social sciences and humanities.
You also want something to which the food is somewhat transparent, but not completely. If the food is completely transparent to what you’re using, then all of the radiation will just pass right through the food without doing anything. And if you use radiation to which the food is completely opaque (like infrared, for instance, as in an ordinary oven), then you’ll just cook the outside using your radiation, and let conduction (which is much slower) do the innards. Microwaves can penetrate some distance into food, but not completely.
No, it isn’t. Consumer microwave ovens run at 2.45 GHz because at the time the technology was invented, that frequency was unused and foods could absorb it effectively, but not TOO effectively–if all the radiation is absorbed by the surface of the food, the inside won’t cook. It is not tuned to a resonance of water, since any such resonances don’t exist as such in liquid water. The “stickiness” of adjacent liquid water molecules makes vibrations “smear out” so that resonances are not well-defined.
The key property of 2.5gHz energy is that it is absorbed by fats, sugars, and water, turning into heat.
Energy of other frequencies is either transmitted or reflected, neither of which will cook food very well. Theoretically you could cook food with EM energy of any frequency of sufficient intensity, but it would not heat food with the evenness that you want. Gamma and X-rays would simply pass right through the food, ionizing it but not heating it very much. Visible and UV light would be mostly reflected.
For the energy that is available from household current, 2.5gHz is the best way to cook food for earthlings.
I’m not sure about sugar, but otherwise you’re correct. There is however a large problem with using 2.45GHz for food, and that is that it’s not absorbed well at all by ice. Fortunatelly most frozen food contains a (varying) amount of free water, and it is this that absorbs the energy. This is why microwave ovens are comparatively bad at thawing food that’s composed of different materials. Try putting a dollop of ice-cream next to an icecube (both of the same temperature), and shove it all in the microwave. The ice-cream contains lots of water that’s supersaturated with sugar, and thus stays liquid, so it will absorb the energy much faster than the ice. [sup]1[/sup]
In the meat processing industry 915MHz is used instead to thaw meat to –4/-3° C.
Sure, it’s the best to cook with, but not the best to thaw with.
[sup]1[/sup]Note, I haven’t actually tried this myself, but based on what I understand about microwves that’s what ought to happen.
It’s fats (including oils), sugars, and water. Perhaps other obscure compounds as well, but those are the main ones. Foods that don’t have one of those don’t heat very fast in a microwave. Previous poster is correct in mentioning that ice behaves differently than water, although there is enough free water in most melting foods to get the process going.
If so, why was this the perfect freq to have those 2.4 Ghz portable house telephones that sit next to you head, transmitting at? Why choose something so resonant with what the human body is comprised of?
This shouldn’t be a problem. You can find an X-ray energy that penetrates an inch or two into water, but no further. (Somewhere around 40 keV would be my guess.)
I think the primary obstacle is the inefficiency of X-ray sources. X-ray sources usually work by bombarding a tungsten target with an electron beam. Most of the energy goes into heating the target (which is usually water-cooled), and only a fraction of the energy goes into the emitted X-ray.
Also, X-rays are far more dangerous than microwave radiation, and the damage to the body is believed to be cumulative. You really don’t want an X-ray generator in your kitchen.
I’m not sure if the ionizing effect of the X-ray would affect the flavor and safety of the food. I would guess not, since irradiation is already used for sterilizing food, but does anyone know?
As stated by Q.E.D., 2.45 GHz is not a magic frequency, and has nothing to do with the resonant frequency of a water molecule. For resonance to occur, you need the EM wavelength to be on par with the length of the object you’re trying to resonate. Now let’s see here… the EM wavelength is 12.2 cm. And a google search reveals that a water molecule is about 2 angstroms long. So the EM wavelength is 1.22 billion times longer than a water molecule. Nope, ain’t gonna happen…
Many things (including water) heat up when subjected to EM radiation. This is because the material absorbs some of the energy contained in the EM wave. There’s a term for this: attenuation constant, a.k.a. loss tangent, a.k.a. dissipation factor. For materials with a very high loss tangent, the EM energy is absorbed very rapidly after the wave penetrates the outside surface (within a few thousandths of an inch). For materials with a very low loss tangent, it is possible for the EM wave to pass through the material with very little energy being absorbed by the material.
It should be obvious, then, that for cooking purposes, you do not want a situation where the loss tangent is very high, else energy absorption will only occur near the outside surface. You also don’t want a situation where the loss tangent is very low, else the EM radiation will travel through the food without imparting much energy to it.
Food usually has a lot of water in it. One of the interesting things about water is that the loss tangent is frequency-dependent. In other words, you can “dial in” the loss tangent you want by simply varying the EM frequency (within limits). It was experimentally found that 2.45 GHz provided a good “middle-of-the-road” loss tangent, i.e. the EM wave was absorbed within 1 or 2 inches (or whatever) after penetrates the outside surface. But there are probably other frequencies which give the same loss tangent for water. My guess is that the range around 2.45 GHz was chosen because it was the lowest frequency, and/or it was found to be the least problematic when it comes to RF interference.
It is kind of interesting to ponder what would happen to a piece of meat if you blasted it with X-rays or gamma rays. I know you wouldn’t “cook” it, and it wouldn’t be “burned” (radiation “burns” are largely a result of apoptosis, necrosis, and concomittant inflammation resulting from detection of DNA damage and the responses that induces; so a piece of dead meat isn’t going to behave that way).
With enough of a dose, would the meat smell or taste much different? I imagine it must, since ionizing radiation is going to change its chemical makeup somehow; but I’ve no idea what sorts of changes one should expect.
You say there is no resonance, but then say that the water somehow absorbs energy from the EM wave. How can you have absorption without resonance? If you pop some water into a microwave spectrometer, you’ll see signals where the microwaves are in resonance with certain transitions between different rotational levels of water. Maybe there is a terminology mix-up here with what we mean by “resonance”. I have never read before that the overall size of a molecule has anything to do with its absorption spectrum.
A resonance is usually considered to be a sharply defined energy level (or spectral line, if you prefer to think of it that way). When you have a relatively complicated molecule like water, though, you’re going to have so many wide resonances that they all sort of blur together, with the result that complicated molecules can absorb whole ranges of frequencies, not just sharply discrete levels.
Regarding the cordless phone thing, microwaves run at some hundreds of Watts while cordless phones run at a few milliwatts. Theres little to no chance of you being cooked by your cordless phone.
It’s simpler than glucose or deoxoribonucleic acid, but it’s a fair bit more complicated than, say, N[sub]2[/sub], or even CO[sub]2[/sub]. All that a diatomic molecule can do is osscillate in one mode, or rotate in two degenerate modes (so effectively only one rotational mode). A bent triatomic molecule like water can oscillate in three modes, and can rotate in three distinct modes, giving it three times as many distinct modes as a diatomic molecule.
