rayiner;339808 Wrote: > Say your microwave cooks a pizza in 100 seconds at 1,000 watts (ie: 100 > kJ of delivered energy). By your reasoning, I can accomplish the same > effect by leaving the pizza next to a 25 watt lightbulb (say 10 watts > actually hitting the pizza) for about 3 hours. Try it sometime --- it > won't work! > > You're misunderstanding the basic physics here. Why does your pizza > cook? Your pizza cooks because you heat it up. It heats up because at > 1,000W, the microwave hits it with far more energy than it can > dissipate. That excess energy is stored, increasing the temperature of > the pizza. On the other hand, the pizza can probably easily dissipate > 10W. You can leave the 25 watt lightbulb next to it for days and its > temperature won't increase much at all.
Can I ask what physics or electrical engineering study you did? I actually studied and applied RF and from what you write I can guess you didn't. A lightbulb generates mostly light at visible frequencies; any heat (IR) is an unwanted byproduct (the bulb is flawed like so many things). The microwave, like the cellphone, generates RF. You can't heat a pizza with light unless it's IR (but IR works from outside-in, ie conventional oven) but you can surely heat it with RF which penetrates the pizza and heats it all trough! rayiner;339808 Wrote: > Also, frequency does matter. There is a reason microwaves operate at > 2.45 GHz. That is a resonant frequency of water. When you bombard food > with high-energy RF at that frequency, the water in the food resonates, > absorbing the RF energy. Once you go a little bit off that frequency, > the resonance effect stops, and most of the RF energy goes right > through the food instead of being absorbed by it. If you ran your > microwave at 1.9 GHz, even at 1,000W, it wouldn't cook your food very > well at all. Sorry, but that is just wrong, you know nothing of the subject. If water would be resonant at 2.45 GHz, we could use it as a medium for global communications (the oceans) and wouldn't need fiber-optic cables, satellites etc. Water will dampen all RF and the higher the freq the more it dampens. Only VLF is usable for underwater communications. Cooking with a microwave is based on what happens with molecules. It makes the molecules rotate. It is called "Dipole rotation" and part of the Dielectric heating phenomenon, read this for more: http://en.wikipedia.org/wiki/Dielectric_heating It also lists the formula from which you can see that the higher the (angular) frequency, the better it works, there is no resonance involved and the effect works even as low as 100 kHz and as high as 300 GHz as listed in the link that follows below; The impact of RF on our body is measured as a SAR value. Specific Absorption Rate, see http://en.wikipedia.org/wiki/Specific_absorption_rate Basically, governments decide what's okay and what's not okay which one would assume can be based on average use of cellphones plus a big safety-margin. The question is if that would suffice for people who excessively use their cellphone. A research-team in Sweden thinks that it is -not- safe for some "successful, middle-aged businesspersons", especially when they complain about headaches. Doctors are advised that this group has a higher risk for brain-tumors because of using their cellphones so much (as their research indicated). I put the link up before, but here it is again: http://www.bio-medicine.org/medicine-news/Use-of-Cellular-Phones-associated-with-Increased-risk-of-Brain-Tumors-1-1/ Pff. just now I decided to lookup "microwave oven" on wikipedia and I should have done that before all else. It reads: " Microwave heating is sometimes explained as a resonance of water molecules, but this is incorrect: such resonance only occurs in water vapor at much higher frequencies, at about 20 gigahertz[5]. Moreover, large industrial/commercial microwave ovens operating at the common large industrial-oven microwave heating frequency of 915 MHz (0.915 GHz), also heat water and food perfectly well. [6] The frequencies used in microwave ovens were chosen based on two constraints. The first is that they should be in one of the ISM bands set aside for non-communication purposes. [...] For household purposes, 2.45 GHz has the advantage over 915 MHz in that 915 MHz is only an ISM band in the ITU Region 2 while 2.45 GHz is available worldwide. " So, no, there's no resonance involved; yes, it works perfectly well even as low as 915 MHz, and the 2.45 GHz was chosen because of ISM/frequency licensing issues and has nothing to do with any resonance frequency at all. I'm sorry I flame a bit here, but pls. write about what you actually know about, and not just statements that you could know are not true by checking it on the web. Anyway, I think we're far from audio power-supply issues, aren't we? ;-) Ciao! Nick. -- DeVerm ------------------------------------------------------------------------ DeVerm's Profile: http://forums.slimdevices.com/member.php?userid=18104 View this thread: http://forums.slimdevices.com/showthread.php?t=52348 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
