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Physics/Ac/Dc converter


QUESTION: A TV that we bought for the bedroom has an ac/dc converter box that connects the tv to the outlet. It is quite close to where we sleep.  My understanding is that it is best to avoid products with those boxes (for health reasons), especially in a sleeping area.  Would it be better to purchase a tv with a regular power cord (and no ac/dc converter)?

Thank you!

ANSWER: It's amazing how many devices are now working on DC these days.  No, the EMF emitted from converters of this type are very low.  In fact, in old tube TVs that converted to high DC voltage that problem was far more significant.  If you want to lower the amount of EMF in your house, consider the biggest sources first, like cell phones.  However, even with direct transmitting devices like cell phones, there's no consistent evidence of even a statistical increase in any health risk.  Cell phones and wifi dwarf the signals from your TV's power converter, and it operates at such a low frequency that you can ignore the converter in your bedroom.  The National Institute of Health maintains many fact sheets on EMF and cancer risk, like this one specific to cell phones:

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QUESTION: Thank you so much for your thorough answer (highest rating)!  One more question based on your response - I had Wifi turned off in my new apt - however, in New York, you can't really escape it - you're getting it from neighbors, outside sources, etc.  In my previous apartment, I was under the impression that I did not have wifi because I couldn't access it on my mobile devices - but I have since found out that I think my modem was in fact emitting it because the corresponding lights were always lit up (even though I didn't have access to it).  I am very upset to find this out because I spent many hours at my desktop computer near my modem.  My understanding is the closer you are to the modem, the worse it is?  At this point, is there anything I can do in my current apartment to reduce exposure?  I use my cell phone in a very limited way, but no one can control their neighbors or street use of Wifi.
Thank you again!

The reason that wifi signals only go a few tens of feet is that they're fundamentally weak from the start.  Your cell phone, which you do use even if it's in a limited fashion, transmits signals all the way to distant towers.  Even if it's not being used, it pings and receives data to/from towers.  This signal is far stronger than wifi, even if it is intermittent.  

If your modem's wifi was inactivated, then that signal should be off...and if it's not, then I wouldn't worry about it due to the low strength.  You're needlessly making yourself stressed by worrying about this issue, and stress can have very powerful and negative effects on your health.  Beware becoming one of the "worried well."  As an example of what stress can do to you, when there was a leak (as usual, caused by metal scrappers opening something they should've never gotten their hands on) of radioactive 137Cs from a scavenged medical source in a defunct hospital, it resulted in people actually playing with the glowing blue salt that contained the radioactive material.  They didn't understand what it was, resulting in one of the unusual incidents in which members of the public were affected by their radiation dose.  This caused major panic, leading to the radiation surveys of 112,000 people.  Whereas 16 people were hospitalized for serious exposure and about 30 more monitored on an out-patient basis for minor exposures, 8% of people surveyed (over 8,000 people!!) had symptoms of nausea.  This was entirely because they were stressed out about radiation, which they can't perceive directly and they didn't understand.  That's a large number of people, most of whom received zero exposure due to the incident.  Stress is a powerful thing, don't stress yourself out.  It will literally make you ill.  And if you don't feel ill, then here's why:

I'm an expert on ionizing radiation, the type that can harm you in large enough doses.  The photons or other particles in ionizing radiation have higher energies than the photons in visible light and can cause chemical bonds to break.  That's why you should wear sunscreen and not get multiple whole-body CT scans every year.  Photons in the visible spectrum are about 1 million times lower in energy than the photons I deal with, and can barely facilitate photosynthesis in plants.  Photon requencies associated with wifi and cell phone transmission have 100,000 to a million times lower energy than the visible light spectrum.  Scientists have neither proposed a reasonable mechanism how they could cause you harm, nor has any such harm been measured.  

So worry about the big issues first, and wear your sunscreen.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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