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Need help understanding potential difference practically

  1. Jan 21, 2017 #1
    I have a problem understanding the concept of potential difference. I get the picture of seeing it as a height difference for example (rock or water that would fall down) but what confuses me is that many times the order of elements in a circuit does not matter. To explain myself better: if I have a battery, an Led and a resistance, no matter if I put the resistance before or after the led, always the same amount of current will flow because what matters is that the resistance has now added another potential drop. This is a bit esoteric to me since is like saying that, though no current is flowing, this different potential is already there. I can see a potential difference as a force which is due to charges that are accumulated for example in a battery but what happens at the charges level when the resistance is added? I get that in the intuitive picture of the height difference this would be like lowering the top of the mountain or placing the valley higher but what happens physically at the level of charges?
    There are ten electrons and ten holes at the two poles of a battery, if I add on one side a resistance, would the charges move to it which means that on the other extreme now I might have only 5 charges (due to the effect of the resistance) and therefore when I close the circuit now I will have less charges moving? But if this would be the case, then a current is flowing even when the circuit is not closed which is not possible, so my idea is not correct.
    Any idea of how could I visualize this more practically since the similarities with mountains and rocks don't work for me?

    Thanks a lot!
     
  2. jcsd
  3. Jan 21, 2017 #2

    davenn

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    hi there Herott
    welcome to PF :smile:

    to save me posting it all again .......
    have a look at what I posted in this thread
    https://www.physicsforums.com/threads/simple-circuits.900746/

    post #4
    just a few days ago, describing potential difference/ voltage drop across one or more resistances
    also describing the current flow

    if that helps or doesn't help .... let me know and we can go further :smile:


    Dave
     
  4. Jan 21, 2017 #3

    davenn

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    yes the potential difference is already there ... doesn't need an external current flowing the PD is the voltage of the battery ..... 1.5V, 12V etc

    a potential difference is created in a battery between the terminals due to a chemical reaction within the battery separating positive and negative charges


    within the battery ? see my previous comment

    or in the external circuit ?

    No, the current will ONLY flow into the external circuit when the circuit is complete
     
  5. Jan 21, 2017 #4
    The rock falling from a height, or the roller coaster going up and down the track, is useful for visualizing kinetic energy vs potential energy in a gravitational field.

    I suppose I'm like many people here, in that I first learned about electrical circuits using the famous water-pipe analogy. It is useful for visualizing electrical current.

    For example, suppose we have two constrictions in series in a pipe. Does the total constriction effect depend on the order of the constrictions?

    http://hyperphysics.phy-astr.gsu.edu/hbase/electric/watcir.html
     
    Last edited: Jan 21, 2017
  6. Jan 21, 2017 #5

    jim hardy

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    It's my opinion this usually stems from a foggy concept of "potential".
    https://www.merriam-webster.com/dictionary/potential
    that's all there is to it, really.

    https://www.britannica.com/science/electricity/Calculating-the-value-of-an-electric-field#ref195494


    Think one step at a time. You're trying to mix analysis of charges in motion with the definition of potential.. Get your concepts nailed down first.
     
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