Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Need Help Urgent

  1. Jan 30, 2004 #1
    Need Help Urgent !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!


    why do we need a complete ciruit required in order to have a continious flow of current.

    An early reply will be appreciated.

    Thanks in advance

  2. jcsd
  3. Jan 30, 2004 #2


    User Avatar
    Homework Helper

    Re: Need Help Urgent !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

    Charge conservation and the principle of relativity:

    div j = ∂ρ/∂t


    ∂μjμ = 0
    (this is the same as above, but you might not have seen it, and it emphasises the relativistic requirement)

    Otherwise, electrons would disappear at one point in space and then reappear at another point in space, and this would violate conservation of charge under the principle of relativity (see simultaneity).
  4. Jan 31, 2004 #3
    I really couldn't disagree less with Turin.

    (That means I agree with Turin.)

    But here's an answer with no tensor calculus involved:

    Connect a light bulb to the negative terminal of a battery. The light bulb is neutral, and the electrons in the battery are repelled by each other. (Opposites attract, likes repel.) So some of them will run through the wire to the light bulb. But pretty soon, there's about the same amount of charge everywhere, or rather, the electrons have arranged themselves so that they are least repelled by each other. Imagine attendees of a party that ended badly, awkwardly trying to avoid each other at another party the following week.

    It's a stable configuration, once they've all found a corner to sulk in, but not very conducive to light bulbs getting lit up.

    To make the light bulb glow, you connect the other side of it to the positive terminal. The electrons are all attracted to this beckoning beacon, and they are much more concerned with reaching the positive terminal than they are with avoiding each other, and to get there they are even willing to pass through the thin filament of the light bulb, heating it to white hot in the process.

    But unless there's a positive terminal to go to, they ain't movin'.

    Forgive me if it seems that I'm anthropomorphizing electrons; I'm actually electrosizing humans.

  5. Jan 31, 2004 #4
    That should go in the who wants to be a liar thread.
  6. Jan 31, 2004 #5

    Thankyopu everyone:smile:
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Need Help Urgent
  1. Satellite Urgent Help (Replies: 4)