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Computer laptops, DC and EMF

  1. Apr 22, 2008 #1
    My background is in CS, so I apologize if I sound a bit stupid wrt the topic at hand.

    My friend and I have been having a heated debate about the causes of "discomfort" that I've been experiencing with my Macbook Pro. After having it on my lap for several minutes, even on top of surfaces that are allegedly nasa-grade insulators, I would feel an unpleasant warm tingling sort of sensation in the 'surrounding area'.

    Heat, I thought, so I installed a software temperature gauge and set the fans on maximum, keeping the CPU core under 90degF. The laptop was even cool to the touch, yet I would still feel the sensation.

    Wireless, I thought, so I turned it off as well as bluetooth. No change.

    Then I started considering electromagnetic fields as a potential source. My friend, however, is convinced that I'm insane. He says that without some sort of coils to amplify the effect, there simply would not be enough current going through the circuits to create a magnetic field strong enough to be felt in the way I'm feeling the effect. The DC current, he says, and the resulting static magnetic fields, are simply not strong enough to be noticeable...

    I'm not at all convinced. I've even read that some laptop monitors alone generate between 5 - 100 mG of magnetic flux which, according to some European standards, is above their acceptable norms. I plan on getting a gauss meter and running a few tests, but in the meantime I'd love to hear any thoughts on the matter...
  2. jcsd
  3. Apr 22, 2008 #2


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    Welcome to PF, Slay2k.
    I've never heard of such a thing.
    Do you by any chance happen to have a medical condition (such as diabetes) that would allow even the minor pressure of a laptop to disrupt the circulation in your legs? Reduced bloodflow can result in the sort of symptoms that you mentioned.
  4. Apr 22, 2008 #3


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    Just because the laptop is not hot to the touch it doesn't mean it isn't a source of heat. Even with all the fans etc the laptop will definitely be above room temperature (15 - 20 C), and as long as it is below external body temp (34 - 37 C) it wouldn't be hot to the touch.

    So say it is at 30 C, the part of your body in contact with the laptop, through some clothes I presume, would feel 30 C which is 10 C above the temperature felt by the rest of your body, hence the warm feeling.

    Also vibration from the spinning hard disk would have an affect, small but maybe enough to have an effect.

    Forget the electromagnetic field idea, it's preposterous; although I'll probably be proved wrong.
  5. Apr 22, 2008 #4
    Thanks and no, no medical conditions I'm a healthy kid :)
    This is true and I've considered this, but keep in mind it is never directly on top of my clothes. I've either used laptop accessories that elevate it 5-6 inches above my body, or a product called "Laplogic W800" (can't post URL due to my low post count, so google if you'd like), which purports to be a top-grade thermal insulator. I figure with those factors in mind, I shouldn't feel nearly as much as I do...
  6. Apr 22, 2008 #5


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    In that case you're right that is odd.

    It suggests to me that the warm feeling is perhaps simply the result of the weight of the laptop on your lap causing a the discomfort. In the same way my arse feels warm and uncomfortable after sitting on it all day in the library
  7. Apr 22, 2008 #6


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    It might also be a purely psychological effect. No offense intended, but a belief or even suspicion that something can happen is capable of manifesting itself as physical symptoms. Those are no less real than if there was a clinical cause. Is there a chance that you just expect something like that to happen?
  8. Apr 22, 2008 #7
    I am also skeptical about any em fields being your problem here, but i could be wrong. Anyway slay2k here are some variables you can narrow down for us without very much effort:

    Can you experience this feeling only when sitting at your computer desk or can you feel it in a certain radius around your computer?
    If so how far before you lose the sensation?

    Does this feeling only occur with your computer while at the office or does it work anywhere?

    Is the feeling produced only by one, by any, or by a certain kind of computer?

    Could you possibly be mentally insane?

    Could your friend be pulling your leg here with some elaborate practical joke?

    Write this stuff down. I think that it might help you figure this out. Good luck!
  9. Apr 23, 2008 #8


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    Regarding this...
    I would go so far as to say that especially when it's not hot to the touch, it is a source of heat. When you installed the new software to keep the fans running more, did the effect get worse? You see, the CPU is going to generate about the same amount of heat in any case. Keeping the chip cooler means more of that heat is being pushed out of the machine, possibly into your lap.

    Have you talked to others about this, and is it a common phenominon? I've never owned a laptop, but I might have to get one!

    Aslo, to add to RpbrtM's list of things to try, try sitting for several minutes with your laptop on your lap while it is switched off. Maybe it is just trapping your own body heat, like sitting with a piece of insulation on your legs.
  10. Apr 23, 2008 #9
    Your legs are blocking cool air from

    A laptop needs a constant flow of cooler air from beneath to cool the system down, that's why they say to never put your laptop on soft surfaces, it sinks and no cooldown happens.

    Look at the bottom of your laptop, you should see four pins that act like "legs" that keep the laptop off the table.
    Last edited: Apr 23, 2008
  11. Apr 23, 2008 #10
    It occurs anytime I put the laptop on top of my body, meaning within less than a foot. It is produced by any laptop machine, I have tried several. I could possibly be insane, yes. And no my friend isn't playing jokes.

    Makes sense, but heat pushed onto my lap doesn't ring true when the laptop is on top of insulating material. But I will absolutely try it with the laptop switched off, this is not a bad idea, I just can't do it right this second since I'm typing on it.

    Yes, which implies again that this is a heat issue with the laptop heating my legs. Which I'm not sure is the case since I've used both an iLap and a LapLogic board to elevate it and allow for air flow underneath..
  12. May 8, 2008 #11
    I don't think I ever paid attention before, but I believe I was just experiencing what you were talking about. I was outside wearing shorts and had my laptop sitting in my lap. Out of nowhere it seemed as though something under the laptop was making my left thigh itch, so i lifted the laptop up to see what was biting me or making it itch. Right on the underside of the laptop, the spot that was making my leg itch, was the plastic laminated 'Contextant Systems' label this is fixed with adhesive to the backside of the access door for the internal wireless card. Only catch is, there's no internal wireless card inside... I removed it four or five months ago. The CPU fan intake was completely unobstructed and the exhaust is blown directly out the back. The ram, which tends to get very hot, is in the very center of the laptop, so it's not because of those.

    The irritation or itching/warm feeling in that spot kept coming back after a few minutes and each time I would again lift the laptop up to look... nothing there. The spot on the laptop wasn't hot either. Warm at best. I believe it has something to do with the laminate getting warm and irritating the skin. That's in my case at least.
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