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Trying to understand Electric Potential

  1. Dec 29, 2014 #1
    I just watched a videos explaining electric potential and voltage in terms of gravitational potential. A negative charge was drawn with electric field lines converging into it and then a positive charge placed in the vicinity. The video explained that work was required to overcome the electrostatic attraction and separate the positive charge to a point farther away from the negative charge - this was compared with lifting a mass against gravity with the energy exerted via work going into increasing the gravitational potential energy of the mass. Thus the work done on the positive point charge also increased its electric potential and also increased the voltage between the positive and negative charges.

    This is where I started getting confused. The author said that as the positive charge is released it will either "fall" back to the negative charge or be used to do work (like falling water turning a water wheel) in electric devices. My confusion comes from the fact that the charge "falling" is a positive charge but I've always understood it as negative charged electrons being the entities that move down potential differences to power electronics.

    Could someone clean up this small confusion and also explain, all other aspects being equal, what a device experiences when connected to a 100v source and a 1000v source? I understand higher voltage carries more energy per coloumb but practically speaking will the 1000v source "fry" or "blow up" a device?

    Thank you
     
  2. jcsd
  3. Dec 30, 2014 #2

    Dale

    Staff: Mentor

    For most purposes there is no difference between positive changes falling and negative charges rising. They do the same work and generate the same B fields and so forth.
     
  4. Dec 30, 2014 #3
    Ok, so it doesn't really matter if I switch the positive and negative charges and make the negative one that moves...the same potential will result.

    One thing I read though that I have trouble relating to this negative and positive charge separation view of potential is the following: a position with a higher accumulation of positive charges will be relatively positive whereas a location with more negative charge will be relatively more negative. How does this concept of charge separation relate to more positive charges = higher (more positive) potential?
     
  5. Dec 30, 2014 #4

    Dale

    Staff: Mentor

    Yes, that is correct. The potential from a single point charge is proportional to Q/r. So it is positive near a positive charge and negative near a negative charge. The total potential from many charges is the sum of the potentials from each charge.
     
  6. Jan 4, 2015 #5
    Okay that makes sense to me; thank you for your input.
     
  7. Jan 5, 2015 #6

    Stephen Tashi

    User Avatar
    Science Advisor

    The conventions of postive and negative were established before the exact nature of electric current was known. These conventions model current as flowing from positive potential to negative potential. For example, analyzing circuits is usually done by drawing current arrows as if current flowed from the positive terminal of a battery to the negative terminal. This pretends a positive charge is flowing. If you follow this convention consistently, you get the right answers. The fact that it's negative charges that are actually flowing the other way doesn't matter except in questions like which electrode in a vacuum tube should be heated.
     
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