voltage across resistors - parallel vs series

Discussion in 'General Electronics Chat' started by lemon, Mar 28, 2010.

  1. lemon

    Thread Starter Member

    Jan 28, 2010
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    2
    Hi:
    I know that the voltage across each resistor in a series circuit is different and the same across resistors in a parallel circuit, but I don't know why.
    Could somebody please help me to understand?
    thank you
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. lemon

    Thread Starter Member

    Jan 28, 2010
    125
    2
    I find the fact that the voltage across the different components in a parallel circuit is the same, counter intuitive because I expect the parallel circuit to split the voltage, as it does the current. But I guess what everyone is trying to say with the water analogy is, if the tap is opened, this is the current flowing. The voltage is just the force/push, that moves the current. The part I find counter intuitive is that if a force is being shared by three avenues, then that force is still being divided up and lessened.

    I just read from your link that the defining characteristic of a parallel circuit is that all components are connected between the same set of electrically common points. So, I guess I need to think in terms of, the voltage just being a reading of a force that doesn't actually travel. It is just a measure of the effect that the resistance is having on the current, taken at any two given points in a circuit. And as all components are connected between the same set of electrically common points in a parallel circuit, then by this definition, the voltage must therefore be equal across those points. Maybe!
     
  4. dsp_redux

    Active Member

    Apr 11, 2009
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    If that is what works for you for now, it's okay. The more you'll investigate, the more you will understand how voltage is often compared to water flow force.
     
  5. lemon

    Thread Starter Member

    Jan 28, 2010
    125
    2
    You mean voltage is water flow force and current as water flow?
     
  6. Ghar

    Active Member

    Mar 8, 2010
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    I don't think you're right about force at all. Consider your own strength, you have some amount of force you can exert. If you triple the mass of what you're pushing you still exert the same force because you're still the same person.

    If you want an actual mathematical analogy with mechanics for this, you get that voltage is force and current is velocity. Resistance is a damper (reactionary force proportional to velocity) and inductance becomes mass.

    https://ccrma.stanford.edu/~jos/pasp/Dashpot.html

    You're not correctly moving to the mechanical analog. Parallel in mechanics means you're applying the same force to each element and then each element can have a different velocity.

    If you want to stay with a water analogy your pump's output has not changed simply because you changed your piping.

    https://ccrma.stanford.edu/~jos/pasp/Spring_Mass_System.html
     
    Last edited: Mar 28, 2010
  7. dsp_redux

    Active Member

    Apr 11, 2009
    182
    5
    Actually, potential is the better word instead of force.
     
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