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I am a non-physics person trying to wrap my head around some EM radiation facts. Please help me with this.

I have read about Dielectric Heating on Wikipedia. And watched quite a few videos on internet on how Microwave oven works. It all boils down to the following facts. Please correct me if I am wrong on any of them.

  1. The Microwaves are absorbed by Water molecule and the Negative charged Hydrogen atoms want to align with negative radiation and Positive Oxygen atom wants to face positive radiation which makes the water molecule dance.

  2. Microwave oven Magnetron changes the negative-positive polarity in charge as often as 2.4 billion times in a second which makes Water molecules dance really really fast.

  3. This dance makes the water molecules heated.

Now coming to my question, I learned that Cell Phones use UHF frequencies such as 800 MHz and 400 MHz.

Does that mean water molecules in our body are dancing at the rate of 800/400 steps per seconds ? Why don't they heat up then ?

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    $\begingroup$ "wrap my head around some EM radiation"; "it boils down to..." - keep those puns coming ;) $\endgroup$
    – ProfRob
    Jul 31, 2014 at 14:38

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Yes you are more or less correct. And cell phones do heat up our tissues but they are very low power (1W compared to a 1000W microwave oven). The water might not resonate but it can absorb energy in these bands. Industrial ovens work at 915Mhz and public ovens are at 2.45GHz (due to regulatory issues)

There is a test in the US called Specific Absorbtion Rate SAR where phones are tested for how much radiative heat they generate and must be below the SAR guidelines. FYI cell phone bands are not 400Mhz, but 700/800/900/1700/1800/1900 depending on where you are.

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POWER. Actually, power transfer. A microwave uses a frequency that water normally vibrates at. A cup of water will boil in a microwave, while the ice cube beside it barely melts. Second, a cell phone operates off a small battery (maybe 100 mW). A microwave oven uses about 1000 watts of energy. Although a cell phone might get the water excited, you wouldn't be able to measure any difference.

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    $\begingroup$ Water molecules contain three atoms and so can vibrate in a number of different ways. This makes calculating their resonant frequency very difficult. However microwave radiation of any frequency will affect them although they may not resonate. Industrial microwave ovens run at 915Mhz and public ones run at 2.45Ghz because that frequency band is open for world wide use without many regulations. $\endgroup$
    – user6972
    Apr 10, 2014 at 4:30

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