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Electricity, eletron flow and very basic electronics

  1. Aug 26, 2007 #1

    sorry if the first question is a bit silly, but my knowlegde of electronics is pretty dull.

    1. Question is about electron flow through a resistor.
    Amps are electrons per time unit, right?
    Voltage is the electrons energy or the amount of energy needed to move them from one point to another, right?
    Conventionel current flows opposite of electrones, right?

    So if i apply 15 volts (of conventionel current) over a resistor and it show 8 volts on the other side, does this mean the resistor has actually accelerated electrons?

    2. Are there any books or sites where i can read about how electrons move in metal and various materials?
    Are there any technical terms or words that would be good to search for instead of just "electrone flow"

    I have gathered over 100 electronic books by now and none says anything about this and i'm not getting any usefull hits when i search.
  2. jcsd
  3. Aug 26, 2007 #2


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    To answer your questions in (1):

    An ampere is defined as a Coloumb per second where a Coloumb is the SI unit for charge, since current is technically charge per time, not electrons per time, though the electrons are the charge carriers here.

    You are close with your definition of a voltage, but you are not quite there. First, you have to understand what a "potential" is. The electric potential at a point in space, is defined as the potential energy per unit charge at that point. So, if you have a particle at a point with electric potential, V, its potential energy, U, is:

    [tex] U=qV[/tex] where q is the charge of the particle.

    One of the reasons we use the potential is that, unlike potential energy, it doesn't depend on the amount of charge you have at that point. The potential is the same for all of them.

    Now that we have covered that, we can talk about voltage. A voltage is a change in potential between two points or a potential difference. (Notice I said "potential," not potential energy.) So actually, the energy needed to move a particle, [tex]\Delta U[/tex], is not equal to the voltage but is:

    [tex]\Delta U=q \Delta V[/tex] where [tex]\Delta V[/tex] is the voltage or potential difference and q is the charge of the particle as before.

    The energy to move electrons from one point to another is directly proportional to the voltage, but not equal to it.

    Moving on, yes, conventional current does move in the opposite direction from the electrons, but in the situation you described above, the electrons would not be accelerated. Consider that the only difference between conventional and electron current is the direction. Now, in that resistor you loose 7 volts. This means (since voltage is proportional to energy) that you also loose energy. The electron current also looses energy by crossing that resistor, but it just does it in the opposite direction.

    I would recommend investing in an introductory physics text, if you do not have one, such as Halliday or Serway if you have algebra and basic calculus knowledge. (if you aren't up on calculus, there are algebra-based texts, but there will be less derivations, and thus formulas appearing without as much justification.)

    You seem to be genuinely interested in electronics, and there is a lot to learn about electricity and circuits in a introductory physics text.

    I hope this helps! :smile:
    Last edited: Aug 26, 2007
  4. Aug 27, 2007 #3
    thank you very much

    thanks a lot for the quick and very good reply... had to read it a couple of times though :)
  5. Aug 27, 2007 #4


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    Anytime. :smile:
  6. Aug 27, 2007 #5
    I think the definitions of current and voltage from the OP are the best for a beguiner.
    The concept of potential is useless for a technician or an engineer because the potential is the difference of potential ( = the voltage ) between a point and the another point infinite away. You cant connect a voltmeter in/to/at the infinite.
  7. Aug 27, 2007 #6


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    I disagree. The potential difference across a resistor is easy to measure with a DVM.
  8. Aug 27, 2007 #7
    Yes, the potential difference not the potential.
  9. Aug 27, 2007 #8


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    Um, okay. Then I think we are all saying the same thing. You don't need to make two measurements with respect to infinity, when you can make one measurement locally on the difference. Fair enough.
  10. Aug 28, 2007 #9


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    I still think that knowing what a potential is is very important to understanding a potential difference. I understand that potential differences are what matter here, but that still doesn't change the fact that it's hard to understand a difference in something if you don't understand that something.

    I also don't agree with what you said about the original posters definitions. I don't think they are best for a beginner. While they were close, they were not correct. I understand that those definitions may seem simpler than the ones I posted, but they are incorrect. All this does is support incorrect ideas and confusion (even if his mistakes, such as the defintion of the Ampere, were only small ones).
    Last edited: Aug 28, 2007
  11. Aug 29, 2007 #10
    From G01:
    Its your point of view, I just showed mine.

    Potential differences and potential ( absolute ) come from the same integral, the first with limits at two points and the second with limits: one point and another point at infinite, so they are the same concept.
    I think, my point of view, that the potential difference is easier of understanding.

    Again your point of view.
  12. Aug 29, 2007 #11


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    Why, then, do you believe that giving a beginner incorrect definitions (such the electron per second definition of the Ampere) is alright? How does this benefit the beginner?
    Last edited: Aug 29, 2007
  13. Aug 29, 2007 #12


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    A volt is 1 joule per coulomb. Note that the potential is usually due to an external source, not the charge itself. It's similar to the fact that gravitational potential energy normally refers to a relatively large source of the gravitational field, and not to a relatively small object within that field, even though the object also has a gravitational field associtate with it.
  14. Aug 30, 2007 #13
    The OP said electrons. I understand that means a given number of electrons. In a electronic circuit the only moving charges are the electrons.
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