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Can a cellular phone demagnetize a credit card?

  1. Jun 25, 2004 #1
    Hi there!

    Can a cellular phone demagnetize a credit card? Why do loudspeakers make a strange noise when the cellular phone rings?

    I don't know the physical explanation to all this. I'd be grateful if you could tell me what kind of electromagnetic wave phones radiate and how they works.

  2. jcsd
  3. Jun 25, 2004 #2


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    1) A speaker can demagnetize a credit card. Since cell phones have speakers, it's conceivable that this can happen. On the other hand, the speakers are quite small, and probably shielded pretty well, so I'd bet it rarely happens.

    2) When your cell phone is about to ring, the tower sends out a message checking to see if your phone is available. Your phone responds with a message saying it is available, at its highest transmission power. This occurs a half second or so before your phone actually begins to ring. Your phone rarely transmits at its highest transmission power, but does so during this phase of the call to make sure the tower hears it.

    - Warren
  4. Jun 25, 2004 #3
    Didn't the myth busters do something like this? Oh wait that was with ele skin walets.
  5. Jun 27, 2004 #4
    Thank you, Warren
  6. Jun 27, 2004 #5
    It takes a pretty large H field to reorient the magnetic dipoles on the strip.
    My degausser uses at least 50 watts to do the job in a 6" torus field at 60 Hz.
    Maybe if you held them tight together ..... ( H is 1/r )
    I can't quantify it but what is the cell putting out ... a watt or two ?
    And might not this be above a cutoff frequency for reorientation ?

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