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Receding Electric field/Magnetic Field?

  1. Nov 13, 2013 #1
    In a circuit, would the electric field produced by emf instantly go to zero upon disconnecting the circuit from the emf source? I would assume there is some sort of time delay. If so, what is it?

    Similar question for a magnetic field: if a conducting solenoid producing a magnetic field is removed from its emf source, how fast would its magnetic field go to zero? I read something about magnetic field decay somewhere, and this article cites 30-thousandths of a second:


  2. jcsd
  3. Nov 13, 2013 #2


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    Too bad the article's author felt a need to add 'sizzle' by mentioning antigravity... The collapse of a magnetic field will depend on a number of variables including its size, strength, and any materials its collapsing through. Your OP also mentioned a circuit, and that could imply components that take time to discharge.

    Certainly they've tried to do their best in this experiment so far. But after reading the article, I need someone to explain something I must be mis-thinking. If they can produce 400+ of these anti-hydrogen atoms, couldn't detect that by a difference in gravitational attraction on the system, with and without the atoms inside? Hmmm... Wouldn't 'falling upwards' cause a difference, exerting the upwards component since locked in the mag field? Am I missing something, or is it just too small to measure with a level of certainty?
  4. Nov 13, 2013 #3
    Is there perhaps some equation that dictates the collapse of the magnetic field and the electric field? I've been searching for some solid constants/formula for such for quite a while, but haven't hit it yet.

    As for the article, my sentiments are similar; however, not sure how demanding the whole "110 times the mass" and the "65 times the mass" are in terms of precision. Would have been nice to provide figures such as the example velocities in the article to get a grasp.
  5. Nov 13, 2013 #4


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    No, the difference in gravitational attraction is exceedingly weak. Much too small to measure for 400 atoms.

    As for the OP's question, check here for a time constant formula for an inductor: http://en.wikipedia.org/wiki/Time_constant#Time_constants_in_electrical_circuits
  6. Nov 13, 2013 #5


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    Thanks, Drakkith. I would've thought the entire experiment was questionable if not for the people performing it and their sources of funding/support. I don't want to push hypothetical ideas at all, so why would anyone postulate that antimatter would fall 'away' from matter? Whether Newtonian or GR physics, matter results in gravity. If matter falls down and anti-matter 'falls up' , why would the two get together and annihilate so easily? Can we kick this around within the realm of standard physics?

    (Maybe a new thread so not to hijaak OP?)
  7. Nov 13, 2013 #6
    Yeah, I'm aware of the Time Constant formula-but that only dictates the rate of change in current and voltage.

    What I am trying to find here is this scenario:

    A typical RL circuit with battery, switch, resistor, and inductor; switch is closed. The inductor is creating a back emf, which is causing a gradual increase in the current through the inductor.

    During this increase (let's say after one time constant for simplicity sake) Switch is opened; electric field, set up by the original battery, goes to 0 after a certain period of delay (?). Or does the field go instantly to zero and there is no current at the same the instant the switch is flipped?

    And presumably, around the similar or same time, the magnetic field produced by the inductor also goes to zero because the current flowing through the inductor has been abruptly changed to zero due to the flipping of the switch. Again, is there a delay in this "collapse" of the magnetic field? Or does the magnetic field go to zero the instant the electric field goes to zero because the current through the inductor is zero? Or is there a delay?

    Hope I'm making sense. Essentially asking about the time delay in the collapse of magnetic and electric field upon the removal of emf source.

    Also, appreciating the discussion on the article as well; it is an interesting article. If somebody could help me out on the OP tho, that would be great.
  8. Nov 13, 2013 #7


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    @Conservation. Maybe you found this already? It doesn't include formulas, but does address what you're describing in technical terminology. Perhaps you'll find better search terms to try. Sorry if I'm too far behind you. <grin>
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