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Cell phone can pop popcorn?

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Bjørn

Wed Jun 11 2008, 06:53AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

I don't believe in the video. Neither do I believe in posting nonsense in the same post as "Anyone dumb enough to believe it, are gullible and should probably be removed from the breeding pool".

There is nothing special about 2.45 GHz, it is just a practical frequency. Here is a nice graph that shows the dielectric losses (and heating) at different frequencies:

As you can see the optimum frequency will depend on what you are cooking, the size of what you are cooking and the temperature.

Steve Conner

Wed Jun 11 2008, 11:29AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

To be fair, the old "Resonant frequencies of water" myth is very widespread. It's hardly worth getting upset about.

Marko

Wed Jun 11 2008, 12:06PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I don't get that point either. The resonant 'frequency of water' thing was something I asked around long ago, and it is indeed nothing special about 2.45Ghz. That does not have anything at all with whether a cell phone can heat things or not.

It seems that someone simply decided to ignore the fact that cell phone is emitting several thousand times less power than a typical microwave oven, and after that most of it is radiated into space rather than being confined in a resonant cavity.

Bjørn

Wed Jun 11 2008, 02:00PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

It is perfectly fair to demand people that want to remove less than brilliant people from the "breeding pool" to know what they are talking about.

Anyone that disagrees can whine about it on Myspace.

Chris Russell

Thu Jun 12 2008, 04:48AM

... not Russel!
Registered Member #1 Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052

I think the best argument to explain how this can't happen is to work through the math.

According to the information here:

Average mass of a popcorn kernel (at worst, site notes bigger kernels are more desirable): 0.133g
Average moisture content of a popcorn kernel at 21C: 15%, or .020g
Temperature at which a popcorn kernel pops: 250C (delta t of 229C)

We know that the heat of vaporization of water is 40.7kJ per mol, or 40.7kJ per 18.0g, or 2.26kJ per gram. This suggests that the energy required just to boil the water in one kernel of popcorn is roughly 45.2J. We also know that the energy required to heat a gram of water by 229C is 958J (4.184J per degree C), which adds another 19.2J to the required energy, upping the ante to 64.4J per kernel.

This means that your average 600W microwave oven should be able to pop 490 (65.1g) popcorn kernels, the amount in a single bag of Act II microwavable popcorn, in about 52.6 seconds. Note that this is assuming they absorb energy at 100% efficiency, there were no other ingredients to heat such as butter, no microwave energy was lost as heat while being reflected off the walls of the oven, no power dissipated by the magnetron due to impedance mismatch, and no heat lost from the kernels by convection. In reality we know that the real amount of time it takes is 2-3 times longer, but at least we know we are in the correct general area.

This also means that in order to be able to pop a kernel of popcorn in 13 seconds, as shown, the total power that those phones must deliver to a single kernel is a staggering 4.95W. Even allowing 2W per phone, this means that somehow an omnidirectional antenna is coupling 82.5% of its energy into a small kernel of popcorn some cm away. Laughable. But it gets worse.

A cell phone is not a microwave oven. There's no reflective cavity, so the microwaves only get to pass through the kernel of popcorn once, rather than many times. Therefore, in order to get as much energy as possible into such a small target, the beam would have to be incredibly tightly focused, well beyond what would be possible even with a well-designed parabolic dish.

Even if a cell phone was capable of emitting a maser-like 2W beam of microwave energy at 2.4 GHz that just happens to be exactly the width of a popcorn kernel, you will not see that sort of efficiency. The half power depth of for the heating of water at 2.45GHz is 12mm. Anything smaller than that will not even absorb half of the microwave energy that passes through it. A 6mm popcorn kernel (the largest size given here:

) would absorb about 30% of the energy that passes through it, if it were made of solid water. Since it's actually only 15% water, now it's only absorbing about 4.5% of the energy that passes through it, and I'm being very generous with the math here. For three phones to deliver that much power to *one* kernel, the phones need to emit a beam of microwaves 6mm wide, containing a total average power of 100W, or 33W per phone.

Folks, that is not a phone, that's a frickin' maser beam of death.

ea6b607

Thu Jun 12 2008, 05:17AM

Registered Member #1320 Joined: Sat Feb 16 2008, 01:31AM
Location:
Posts: 67

just to prove you wrong I think I'll make a huge amplifier and use it to amplify my cell phone signal to 2kw and put it through a directional antenna. Powered by a large car battery bank and place it all in a 400lb back pack. Still mobile still a phone and it CAN pop popcorn. So wher do I start?

Steve Conner

Thu Jun 12 2008, 09:46AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I suddenly had a scary vision of a sort of microwave drag race, where geeks hot-rod their ovens to pop a whole bag of popcorn as fast as possible.

You could make a party of it and eat all the popcorn with beers afterwards.

Nik

Fri Jun 13 2008, 04:20AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

I would overclock my magnetron up to the THz level and use dark coloured corn

. Does any one know where that "resonant water" stuff even started? It seems way more complicated then the true answer of "absorbing radiation makes stuff hot."

Backyard Skunkworks

Fri Jun 13 2008, 06:02AM

Registered Member #1262 Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451

Likely, someone mistook dielectric heating through vibration as some kind of resonance. The fact that dielectric heating occurs across a broad spectrum of frequencies obviously got forgotten.

I recently wrote a school paper on bull... uh cell phones causing cancer. It's a really wide misconception that dielectric heating for water is limited to 2.45ghz or some other mystical frequency. It's also a wide misconception that everything that involves "OMG RADIATION" causes cancer.

I even ran across one site where someone went ballistic because their magnetic field meter measured... 10milligauss.

The fact is, anything related to cell phones causing strange effects like popping popcorn, let alone cancer, is pure BS.

Cell phones put out way less power than a microwave oven, normally on the order of a watt or less each. Maybe thousands of cell phones, all with some type of focusing coil, could heat popcorn. Thats about it.

Chris Russell

Fri Jun 13 2008, 07:11AM

... not Russel!
Registered Member #1 Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052

Dr. Conner wrote ...

I suddenly had a scary vision of a sort of microwave drag race, where geeks hot-rod their ovens to pop a whole bag of popcorn as fast as possible.

You could make a party of it and eat all the popcorn with beers afterwards.

Interestingly, while searching for information for my post above, I saw an interesting method of popping popcorn, apparently in use by street vendors in San Francisco. Apparently they heat the popcorn and oil in a sealed, high pressure container of some sort, and at some predetermined temperature and pressure, they place the contraption in a large bag and release the seal, whereupon all the popcorn pops at once with a mighty kaboom, filling the bag with steaming hot popcorn in an instant. The heating process is presumably not very fast, but that's a delivery system with some showmanship!

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