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Single wire transmission

  1. Oct 29, 2011 #1
    https://mail.google.com/mail/?ui=2&...&th=13350dc1754a8105&attid=0.0&disp=inline&zw

    Can someone explain why the source must also be hooked up to ground. I know it completes the circuit but whats the point? Why wouldn't current flow without it? Since the line is at a positive potential then there is a resistor(acting as a house) then house is connected to ground. Seems as if current should flow from high to low potential.

    Having a dumb day can't figure stuff out.
     
  2. jcsd
  3. Oct 29, 2011 #2

    berkeman

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    Your link requires a secure sign-in and password. Can you post is in the clear somewhere else?
     
  4. Oct 29, 2011 #3
    1029111104.jpg
     
  5. Oct 29, 2011 #4

    berkeman

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    Yes, in this circuit the source has to be grounded. Otherwise the circuit is not complete, and no current can flow through the signal source.

    Alternately, just draw a wire across the bottom of the signal source and the load resistors, and get rid of the ground symbols. They just represent a common connection in this problem anyway.

    Think of the signal source like it was a battery. You need to connect to both the + and - terminals of a battery to get any current out of it, right?
     
  6. Oct 29, 2011 #5
    So without a complete circuit is there a way to hold the voltage constant at the source and draw current when necessary?

    If you had a van de Graff(not touching the ground) and a wire hooked up to the top connected to resistor that connected to the ground, shouldn't it have a steady current.
     
  7. Oct 29, 2011 #6

    berkeman

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    I don't know much about Van de Graff generators, but no, without a complete circuit, no current will flow. Keep thinking about my battery illustration. If you connect only one end of a battery to anything, nothing happens, right?
     
  8. Oct 29, 2011 #7
    I believe you on the battery and everything and that makes sense but I don't understand why my Van de Graff example will not work..
    As long as there is build up of electrons in the ground then there will be no counter electric field and it should work.
     
    Last edited: Oct 29, 2011
  9. Oct 29, 2011 #8

    berkeman

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    Look at the figure at the wikipedia page for the VdG generator:

    http://en.wikipedia.org/wiki/Van_de_Graff_generator

    It shows a complete circuit, right? The electrons get pumped to "ground" or the - return lead. The arc that gets drawn across the gap flows as the same current all throughout the circuit.
     
  10. Oct 29, 2011 #9
    If you had a van de Graff(not touching the ground) and a wire hooked up to the top connected to resistor that connected to the ground, shouldn't it have a steady current.

    That's my question. I just used the van de Graff in my question becuase it provides a constant voltage and charge on surface.
     
  11. Oct 29, 2011 #10

    berkeman

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    Looking at the figure at the wikipedia article, it does not matter a bit if you hook "ground" or "Earth" or a pink poodle to the - connection. The current flows around the closed path shown in the figure.

    (Not that I have anything against poodles)
     
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