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Ampheres, Volts, Ohms, Watts

  1. Oct 8, 2014 #1
    I've been trying to brush up on my electrical engineering skills and have been working on the circular and redundant terminology of amps, volt, ohms and watts.

    It seems to me it all comes down to a quantity of electrons (i.e. coulombs).
    And, for various reasons perhaps the number of electrons over a period of time (e.g. 1 coulomb per second)

    So, it seems like all the other terminology: amperes, volts, ohms, watts, etc... is just redundant obfuscation of the simple measurement of electrons.

    Why doesn't my residential electricity provider just bill me in coulombs (C) each month. Why do we have such ridiculous concoctions like kWh?

    I've been reading other explanations on the web where the issue comes up and you see the ridiculous and incredibly inaccurate explanations involving water pipe analogies and other circular explanations that do not even come close to explaining that the plethora of electrical terminology is just dozens of redundant terms that all mean the same thing.

    Am I missing something?

    Thanks...
     
  2. jcsd
  3. Oct 8, 2014 #2

    russ_watters

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    Welcome to PF!

    Volts and coulombs are not directly related. Now if everyone was connected to the same service voltage, you could indeed bill for coulombs, but since they don't, you need to combine the coulombs and volts to find how much energy they supplied you (which directly translates into how much fuel they spent to make it.

    Those other terms also have different and useful meanings, but unrelated to the example you gave.

    For example, you know amps is coulombs per second, right? So they are similar but not interchangeable.
     
  4. Oct 8, 2014 #3

    Drakkith

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    Consider a circuit carrying 10 amps of current at 10 volts. Since power is P = VI, then the power is 100 watts. No consider a circuit with 10 amps of current at 100 volts. Same amount of current, but different voltage. Power is now 1,000 watts. So even though we are talking about moving electrons, we are not talking solely about moving electrons. We have to consider the potential difference which causes them to move in order to find the energy and power of the circuit.

    Because KWh's is a measure of power usage, not current and not the number of charges. As shown above, you can have the same number of charges passing through a point the circuit yet the power usage can be many many times more or less.
     
  5. Oct 8, 2014 #4
    The definitions are interrelated but certainly not circular.

    You can take water as an analogy.

    The current, measured in Amperes, is how much water flows per second, say through a given pipe.

    The voltage, measured in volts, is the difference in height between the entrance and exit of the pipe.

    Charge, measured in Coulombs is the volume of water.

    and so on and so forth.

    (You can't take this analogy too far, because the behavior of water is much more complicated than that of electricity)
     
  6. Oct 8, 2014 #5

    SteamKing

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    Yes, quite a lot. These terms all describe different things, of which you seem oblivious.

    An ampere is the measure of the flow of electric charge. 1 Amp = 1 coulomb of charge (which itself equals approx. 6.24*1018 electrons passing a given location in 1 second. Think of an ampere as the amount of flow of electricity.

    A volt is the potential difference between two points in an electrical conductor. Think of voltage as analogous to the pressure in a pipeline.

    An ohm is a unit which measures the resistance of the electrical current flowing in a conductor. A resistance of one ohm is equal to a change of 1 volt when 1 amp of current is flowing.

    A watt is a unit of power, or how much energy or work is delivered in a unit amount of time.

    Your power company doesn't bill you for the number of electrons furnished to you, because a bag of electrons, by themselves, aren't capable of doing any work for you. Your power company is furnishing you a certain amount of work to run all of your lights, appliances, and other electrical gadgets, which is why your bill shows how many kW-h of electricity you used each month. If your utility company put a steam engine in your house to drive some gadget, like a water pump or a fan, you'd still get a bill measured in kW-h for the usage of this steam engine.

    Keep going. You've still got a lot of brushing up to do.
     
  7. Oct 8, 2014 #6
    Thanks Russ, and yes... that's my point... amperes is coulombs per second. Why make up all this useless terminology. I see countless amounts of time on the internet wasted where individuals are struggling to understand useless, redundant terminology. I think it would not be so bad if each such discussion started out by saying the terminology is redundant ratios of the number of electrons and have no clear differential purpose.

    In my opinion... the International System of Units has a lot of work to do.

    I wouldn't be making a big deal about this if I didn't see my own kids (who are extremely adept in problem solving) being turned off by the useless memorization of terminology that has no function.

    I've seen a conference room of people suddenly come out of a moribund atmosphere and become excited when the subject of naming or creating the name for something comes up. I do not know why people are predisposed to that behavior.
     
  8. Oct 8, 2014 #7

    Drakkith

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    The terminology isn't useless, you just don't understand it correctly, as pretty much every post in this thread explained.
     
  9. Oct 8, 2014 #8
    Drakkith, thanks for the reply. Sorry, but I disagree with your comments. Amps, volts and watts are all ratios of electrons per unit of time. They are useless and redundant concepts. Coulombs is not a ratio... it is a specific number of electrons. It is simpler and more clear to say electrons per second... especially if you are trying to teach this to children.
     
  10. Oct 8, 2014 #9
    The SI system replaces older ones where the conversion between units was completely aleatory. Having a unit for charge that is the product of the units of time and current is totally logical. Of course you could just write Ampere-seconds, but in many cases using Coulombs is more practical. Note that many things do not have their own unit, e.g. speed is measured in m/s rather than cheetahs, snails, crusades or whatever, and areas and volumes are measured in units of length squared (m^2, mm^2, km^2, ...) or to the third power.

    In any case, if you use the system regularly, the units come naturally.
     
  11. Oct 8, 2014 #10
    Amps and Volts are base units that are needed to generate all the others, just like seconds. They cannot be replaced or absorbed by other electrical units unless you base everything on Amps and Joules (units of energy).

    You could in principle replace the unit of charge (coulomb) by the elementary charge. This is sometimes done in theoretical physics. In everyday electrical engineering, however, this is impractical. Nobody wants to drag around 10^23s left and right. But you *still* need a second base unit.

    C = A s; A = C/s
    W = J/s = V A
    J = V A s = V C
    F = C / V
    Ohm = V / A
     
    Last edited: Oct 8, 2014
  12. Oct 8, 2014 #11
    SteamKing, thanks for your reply. With all due respect I must disagree with your comments. I'll just point out one thing to better make my point. Voltage is not analogous to pressure. Voltage is a ratio involving a quantity of electrons over time. Pressure does not include a time element.
     
  13. Oct 8, 2014 #12
    \\

    That is wrong. Voltage does not have any notion of time at all.

    Voltage is a ratio of energy per charge. You need one Joule of energy to transfer 1 Coulomb of charge over a voltage difference of 1 Volt.
     
  14. Oct 8, 2014 #13
    M Quack, thanks for your reply. I must respectfully refute your assertion. Joules is a ratio of mass, distance and time. It is not directly related to charge (i.e. coulombs) which is measured in a quantity of electrons.

    You do bring up a good issue. There is probably an interesting relationship between Joules and Coulombs... but, something that interesting would never be found in a school text book.
     
  15. Oct 8, 2014 #14
    M Quack... a Volt is 1 Joule divided by 1 Coulomb. A Joule is a ratio involving time.

    I think Joule is an excellent concept... as good as (but completely unrelated to) Coulomb.

    I still think amps, watts and volts are a waste of time.
     
    Last edited: Oct 8, 2014
  16. Oct 8, 2014 #15
    I disagree.

    The Joule is the unit of energy which is something static not involving time. Power (measured in Watts) is the change of energy per unit time (1W = 1J/s), so power has a notion of time.

    The Coulomb, as you pointed out, is the unit of charge. A given, fixed number of electrons will always have the same, constant charge. So no notion of time here either.

    The Ampere is the unit of current. Current flows, and is therefore related to movement. Movement is clearly something that has a notion of time. Measuring current is making electrons jump through a hoop, and counting how many you get per second or so.
     
  17. Oct 8, 2014 #16
    If you take your ideas a couple of steps further you end up with natural units, i.e. units that are completely based on universal physical constants.

    Wikipedia list a few reasons why this is not used in everyday life - skipping the tiny detal that we still cannot convince certain people not to base their measurements on the approximate size of body parts of dead people and similar concepts.

    http://en.wikipedia.org/wiki/Natural_units
     
  18. Oct 8, 2014 #17
    M Quack,

    First, as you demonstrate in the equations you provide, they are redundant ratios of the same thing.

    Second, all of the equations you provide are expressing a quantity of electrons within a time period. They provide no useful purpose. Electrons per second is sufficient for any and all discussions.

    Lastly, I have no problems with any measurement term involving a simple specification of time, distance, mass or charge. Coulombs is as good as any other term I've seen to specify a quantity of charge.

    I see no reason to make up additional names for something like distance beyond something like meter. Why would I make up some ratio like 1 divided by meter and give it a name? Just say "per meter".
     
  19. Oct 8, 2014 #18
    M Quack, yes you make an excellent point. I unfortunately live in a country not using the metric system. Dealing with human nature is problematic.

    But, I would hope scientists could be more rational. I would hope the community would help push everyone to more logical units of measure such as coulombs and away from ridiculous ones like kWh.
     
  20. Oct 8, 2014 #19

    russ_watters

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    So.... You've now been shown several examples of the fact that you misunderstand what the units mean (specifically, joules and volts not involving time). You need to change your approach here: stop claiming there is a problem with how the units are used by scientists and start learning/fixing your understanding of them.
     
  21. Oct 8, 2014 #20
    https://en.wikipedia.org/wiki/Joule
    J = kg * m**2 / s**2
    s = seconds

    Joules is a very important unit of measurement.

    I can't think of a simpler way to express an unit of energy as equal to moving a unit of mass over a unit of distance within a unit of time.
     
    Last edited: Oct 8, 2014
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