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I noticed that both microwave oven and Wi-Fi use the same frequency band 2.4-2.5 GHz. Yet microwave oven will certainly fry a living being the Wi-Fi has not done yet I suppose. So why is Wi-Fi harmless and microwave oven harmful to us?

Why won't our bodies absorb the Wi-Fi energy through dielectric heating like it does if put in a microwave oven?

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  • $\begingroup$ It's not only just the frequency that counts, but also the intensity. It's like the difference between standing next to a lit match and a bonfire. $\endgroup$
    – Hasan
    Nov 30, 2013 at 16:46
  • $\begingroup$ Power matters. WiFi has very low power. But if you take off plastic "peel" from WiFi antenna and nake the metal, you can burn your skin from it. $\endgroup$
    – Suzan Cioc
    Nov 30, 2013 at 20:56
  • $\begingroup$ Obligatory xkcd. $\endgroup$ Dec 1, 2013 at 1:24

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Our bodies do absorb Wi-Fi energy, which causes the signal to attenuate. The thing is that the signal is so weak compared to a microwave oven that our bodies are able to get rid of the extra energy as fast as we accumulate it. Your skin just isn't going to heat up measurably.

If you stand to close to a radar transmitter, for example, you will experience some discomfort (apparently this is how the idea of microwave ovens came about)

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    $\begingroup$ +1, although NEVER stand near a radar transmitter! Thankfully, we're aware of such things and you won't be able to do this these days without cutting through razor wire fences or, if this is impracticable, being very explicitly told where you can and mustn't go (navy ships have forbidden zones clearly marked around antennas). I knew a fellow about thirty years ago who was no more after a transmitter was accidentally switched on whilst he was working on it (some blockhead took the safety tags off the transmitter's controls). He died about two months afterwards. $\endgroup$ Dec 1, 2013 at 1:22
  • $\begingroup$ PS: You have a great grasp of a really broad range of physics: would you care to add a few words on your background on your user page - if you want to (I know many people are more private than I am). $\endgroup$ Dec 1, 2013 at 1:27
  • $\begingroup$ Thanks. I've added some stuff although probably as thorough as to be pointless :) $\endgroup$ Dec 1, 2013 at 11:43
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First of all, the Wi-Fi doesn't have a defrost setting, we have that going for us. Jokes aside, I looked at the microwave and Wi-Fi that I have, and the first major difference is the power level. The microwave outputs $400W$ to $2kW$ where the for the Wi-Fi is just around $5W$. Also, the microwave runs on a single frequency in a very confined and shielded space. So all that power is focused in a small region of space. Where as for the Wi-Fi, all that energy is radiated "symmetrically". So your body will receive only a small fraction of its output. But if you where to surround yourself with hundreds of Wi-Fi's my guess is that you'll start to feel some discomfort.

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  • $\begingroup$ You meant to say power density I suppose $\endgroup$ Nov 30, 2013 at 16:44
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    $\begingroup$ Yes. But I think in this context, just saying power is enough. $\endgroup$
    – vnb
    Nov 30, 2013 at 16:47
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    $\begingroup$ Yes, the fact that we aren't inside a small resonant cavity is a plus :) $\endgroup$ Nov 30, 2013 at 17:00
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    $\begingroup$ Wi-Fi does not emit 5W of power! That would cause a number of problems: overlap with other networks, dielectric heating, battery consumption just to name a few. Instead it is limited by law in many countries to 100mW. $\endgroup$
    – Alexander
    Nov 30, 2013 at 22:43

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