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Homework Help: Conceptual Question about Voltage Drops

  1. Jun 4, 2015 #1
    • Warning Issued: Formatting template not used for homework question
    So I have one last roadblock to understanding how circuits fully work and it has to do with currents (in series). To my current understanding, if we were to have a simple DC circuit with one battery at 10V and one resistor at 10 ohms, the current at all points in the wire is 1 A. Now, if we were to connect another resistor of 10 ohms, the current would be then be .5 A.

    I am essentially trying to figure out how is the current determined in the wire before it encounters any resistors. What I don't understand here is how is it possible for the electrons to know what speed to travel with when it doesn't know the resistances that are ahead of it? Shouldn't as much charge as possible be trying to escape the terminal of the battery regardless of the resistors ahead?

    If the way I'm explaining it doesn't make any sense, I will gladly offer up a different explanation.

  2. jcsd
  3. Jun 5, 2015 #2


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    I always find it helpful to think of current as being like a bicycle chain. It doesn't make any sense to try to think of one link in the chain moving by itself. Either all links move at the same time or no links move.
  4. Jun 5, 2015 #3


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    Watch "surface charges and circuits" on youtube.. Answer to your doubt lies in the surface charge feedback theory...You need to understand the very initial transient (which lasts for a few picoseconds) which is hardly discussed in the circuits course..
    Last edited: Jun 5, 2015
  5. Jun 5, 2015 #4


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    The electrons move inder the influence of the electric field which propagates
    through the whole of the circuit. The field is setup by the power supply and
    its propagation is influenced by the components in the circuit. I tend to think
    of the situation like the ocean (electrons) and islands (the components), except
    that the current goes through the islands under the influence of the pressure
    difference (as evident by the waves present there) created on the shores of the islands.
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