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Homework Help: Circuit/electric potential question

  1. Mar 7, 2010 #1
    My textbook says that a battery in analogous to a water pump- it pumps water (charge) uphill, which subsequently flows downhill. What I'm confused about, then, is why charges in the circuit wouldn't lose all their potential energy even without a resistor? If they are flowing "downhill" through the circuit wouldn't their potential energy be lost even without something to dissipate it?
     
  2. jcsd
  3. Mar 7, 2010 #2
    Perhaps I didn't understand your question, but are you asking if a battery would loose it's potential energy if we short-circuit it?
     
  4. Mar 7, 2010 #3

    lightgrav

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    Homework Helper

    you're right ... some "resistors" are made of wire.
    with enough current, even THICK wire has significant resistance.

    ResistANCE is a property that ALL objects have ;
    a resistOR is a device made especially to have a constant specified value of resistance.

    So, the charges can lose their electrical Potential Energy even in good wires .
     
  5. Mar 7, 2010 #4
    No, sorry I know the wording is confusing.. Basically, using the analogy of "water pumps" I imagine a battery as taking water from the ground, pumping it to a higher level and therefore increasing it's potential energy. Then, going through the circuit, it flows downhill. Imagining that charges are analogous to the water.. flowing downhill through the circuit.. wouldn't all potential energy be lost by the time they reached the negative terminal? Why do we need resistors to decrease voltage?
     
  6. Mar 7, 2010 #5
    Okay thanks for the reply. I still don't really understand why they wouldn't lose their potential energy even if there wasn't resistance.. Like when you have a positive charge and a negative charge, once they come together the potential energy of the system is zero. If an electron is leaving the negative terminal, wouldn' t it's potential energy be zero by the time it reached the positive terminal?
     
  7. Mar 7, 2010 #6
    The electrons will lose all their potential energy when going from the negative to the positive
    terminal of the battery.
    The heat will always be dissipated somewhere. Batteries have an external resistance that
    will limit the shor circuit current and will dissipate the energy.
     
  8. Mar 7, 2010 #7
    They would, if there were no resistors, a huge current would start to flow. The current is a result of flow of electrons.

    As this current is flowing, the majority of electrons on the - side is traveling to the + side and because of that, the voltage is decreasing. So it is analogous with the water flow.

    But it makes me wonder thou, if we had a perfect conductor to what would the energy be transformed into (since heat isn't an option now)? Electron movement?
     
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