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Fuses and grounding in a circuit

  1. May 11, 2012 #1
    When I ground something, how does the electrons actually flow into the earth? Since it is not a complete circuit whereby electrons flow back into the battery such as in cases like a battery connected to a bulb. I always thought a complete circuit was required so how can the electrons "choose" to flow into the earth without going back to the source? On another note, if my source has a pd of 10V, will the potential at the bulb be 10V and O st the earth's point of contact?

    When I touch the live or neutral wire, why won't the fuse melt? Is it because I'm taking the V=RI of my body and the circuit around it. So the resistance of me is very high so the I would be very low compared to when before I touch the live? But in that case, won't there be a parallel branch whereby one continue through the main circuit and another through me? So in that case what would be the explanation for this?

    Thanks for the help guys! :smile:
  2. jcsd
  3. May 11, 2012 #2
    If I understood correctly, you're talking about a situation in which you ground something, e.g. an electrode which is charged, and electrons then just flow into the ground. The difference is that this current is not a steady state current. It's a transient. They just flow out and they're gone. Now to draw a continuous current you need a closed circuit - there has to be a loop, which charges are continuously pumped around.

    Regarding the second bit, you're totally correct. Perhaps your resistance is so high that the voltage doesn't even manage to "break down through you". And yes in that other case you would be a parallel branch. But verify yourself, from maths and by intuition, that adding a very high resistance parallel branch, doesn't change the net resistance too much. The extra branch draws a very small current, and effectively doesn't change the currents flowing in the rest of the circuit significantly.

    Hope that helps
  4. May 11, 2012 #3
    Thanks for the help! It explained a lot to me. But when dealing with grounding cases, how do I determine the effective resistance? Since its not like a normal parallel branch where it goes back to the circuit..

    Thanks so much for the help!
  5. May 17, 2012 #4
    I would be more clear if you gave a specific example. But whenever you have a grounded node, its potential is defined to be zero. If you have another - its potential is zero too, and basically - they're connected to a common ground node - so they're connected together.
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