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B What is Voltage really?

  1. Jul 22, 2016 #1
    Hello, i was wondering if somebody could give be a better explanation of what voltage really is. Its has been explained to me that the voltage of an electron can be thought of as holding a ball at certain height representing the potential energy of the ball which is then converted into kinetic energy as the ball falls and that voltage is kind of like that. I was wondering if there is any more clear explanation for what voltage really is, as this analogy does not really explain what allows electrons to have different amounts of energy, as an battery can not just move an electron higher up, Thanks.

    Just a thought but could voltage be thought of as the speed of an electron?
     
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  3. Jul 22, 2016 #2

    Simon Bridge

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    The description you have is the accurate description of what voltage is.
    "Voltage" is a casual term used to refer to the difference in electric potential between two places. It is derived from the SI unit used to measure it.

    See: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elevol.html
    Voltage is not properly though of as the speed of an electron any more than the gravitational potential can be though of as the speed of a mass. Much as a mass on a shelf has gravitational potential energy (so the shelf has a gravitational potential) and yet is stationary, an electron may have electrical potential energy, and so be in a position that has a voltage, and yet be stationary: ie if it is levitated between plates of a capacitor.
     
    Last edited: Jul 22, 2016
  4. Jul 23, 2016 #3

    sophiecentaur

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    You seem to be after a 'more familiar' explanation, rather than a 'better' one. Potential Difference is very well defined in conventional EE and that is the best thing to stick with. Trying to re-state such definitions in friendlier terms can lead you up the garden path eventually.
    That may seem to be an elitist remark but EE is a very well structured study and has answered all the more straightforward questions - where QM and Relativity are not involved. So it is as well to go along with it and follow the existing rules of the game.
     
  5. Jul 23, 2016 #4
    I think the analogy still works. Why does a ball held up high have more energy than a ball resting on the ground? Why does that extra energy get converted when it moves towards the ground?

    Same as an electron moving between two points with a voltage.
     
  6. Jul 23, 2016 #5

    sophiecentaur

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    That statement adds nothing to the conventional description. It is just in your own words. The only difference is that you use the word "electron" which is more specific than the word "charge", which covers more possibilities. Also, the question "why" is not in the spirit of true Science which does not try to answer it.
     
  7. Jul 23, 2016 #6

    David Lewis

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    Energy is only part of the equation. Voltage is the ratio of energy to charge. If you double the amount of electric charge, voltage will be cut in half for a given amount of energy.
     
  8. Jul 23, 2016 #7
    Voltage is simply the amount of work (which is force integrated with respect to distance) you need to do on a charge, per unit charge in moving the charge between two points in an electric field.
     
  9. Jul 24, 2016 #8
    It was not intended that the statement add to the conventional description. It was intended to explain how the analogy remained applicable. We are in a teaching forum, after all.
     
  10. Jul 24, 2016 #9

    sophiecentaur

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    If you want an answer to the question about "why the energy gets converted", it's because the Potential energy of a falling body is transferred to kinetic. When a charge moves through a conductor, any change in Electrical Potential is because work is done (as in a motor) or the conductor heats up (Resistance). If a car goes downhill with the brakes on, its original Potential Energy is transferred to heat in the brakes plus a bit of KE due to its small but finite speed downhill.
    The "analogy" that you are looking for is valid because Potential is a concept which applies to all sorts of fields.
     
  11. Jul 24, 2016 #10
    I do not see the point of this conversation. My comment was directed at the original poster to assist with their understanding.
     
  12. Jul 24, 2016 #11

    sophiecentaur

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    Well, yes but we all expect to have ideas in our posts to be challenged to some extent. That's what tends to happen on forums.
     
  13. Jul 24, 2016 #12
    Voltage is like water pressure,think squirt gun, high voltage but low amps (amps==amount of water), open garden hose, low voltage, high amperage, firehose, high voltage with high amps, very powerful, its important your analogies keep the relationship between volts/amps
    While no analogy will capture the true relationship as well as mathematics does, it can be useful in getting a grip on the concepts.
     
  14. Jul 24, 2016 #13
    You don't challenge anything, you misunderstood my intentions and then added your own response.
     
  15. Jul 24, 2016 #14

    sophiecentaur

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    You could, perhaps, have stated it differently. You used the "why" word twice and that is not very appropriate - for reasons I have already given and that is what I was challenging, mainly. If you would take issue with that then hear what Richard Feynman has to say about the "why" question. (Easy to find on Youtube).
     
  16. Jul 24, 2016 #15

    sophiecentaur

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    You could have added the idea that Pressure times flow rate gives an indication of Power. That strengthens the analogy.
     
  17. Jul 25, 2016 #16

    David Lewis

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    What do you mean by "unit charge"? Would it be correct to put the charge upon which the work is being done in the denominator instead?
     
  18. Jul 25, 2016 #17

    sophiecentaur

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    The Unit Charge would be the Coulomb in the SI system. Using the word "unit" means that the formula can be applied to any system of units.
    In gravitational theory, the Unit Mass tends to be used so that SI or Imperial units can be used with the same formulae.
     
  19. Jul 25, 2016 #18

    David Lewis

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    Thank you. What if the amount of charge being energized is not one coulomb? (Or not one unit of whatever system you use to measure charge?)
     
  20. Jul 25, 2016 #19

    Drakkith

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    Then your numbers change, but the concept remains the same.
     
  21. Jul 25, 2016 #20

    sophiecentaur

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    I had the privilege of learning my first few years of Physics with Imperial Units and then grew up to use cgs, MKs and then SI. I had to forget the number 32(ft/s2 then learn 981cm/s2 then finally moved on to 9,81m/s2 for the acceleration due to gravity but the formulae remained the same. Coulombs were always the same unit for my charges though as I didn't use esu's and emu's in anger (at least I don't remember them at A level).
     
    Last edited: Jul 26, 2016
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