What is 1.5V, 9V or 12V really means?

Discussion in 'General Electronics Chat' started by dtvonly, May 13, 2015.

  1. dtvonly

    Thread Starter Member

    Dec 14, 2012
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    Hi. By definition, "...Volt is a potential energy difference between two points....."
    So what is 1.5V, 9V or 12V really means?
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    It means that if you put a fixed value of resistance across it, then a proportional amount of current will flow. That current is proportional to a certain amount of charge for a fixed amount of time. That's what it all means. What were you expecting -- something deep and profound?
     
  3. WBahn

    Moderator

    Mar 31, 2012
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    By definition, 1 V is a potential energy difference of one joule PER COULOMB of charge between two points.

    That answers your question.

    1.5V means that there is a potential energy difference of 1.5 joules per coulomb between the points where that potential difference is measured. Similar for 9V, 12V, or 480,000 V.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    voltage is the measurement of electric force between two points of the same circuit, the bigger the force the bigger the voltage is displayed.
     
  5. wayneh

    Expert

    Sep 9, 2010
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    "Force" is a mechanical term and I don't think it's appropriate for describing voltage. "Potential" seems to be the preferred term.
     
  6. WBahn

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    Force is measured in newtons, not joules.

    The electric field is a measure of the electric force (per unit charge) at a point in space.

    The voltage is a measure of the work (per unit charge) done in moving between two points in space.
     
  7. Dodgydave

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    Jun 22, 2012
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    ErnieM likes this.
  8. Papabravo

    Expert

    Feb 24, 2006
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    Semantic hairsplitting. Check the fundamental units -- they never lie.
     
    Last edited: May 13, 2015
  9. WBahn

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    It's an inherited travesty due to the sloppiness of previous generations made at a time both when things weren't nearly as well understood and also when rigor and consistency weren't as valued. Using the term "force" in this context is deprecated and causes all kinds of confusion because you tell people that something is a "force" when it isn't and, not surprisingly, they think that it is a force, when it isn't. This is made all the worse since there very much IS an electric force, namely the force exerted on one charged particle by all other charged particles.
     
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  10. WBahn

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    The term "force" is perfectly applicable in the electromagnetic realm, but you are correct that it is not appropriate for describing voltage because voltage does not describe a force. The very notion of voltage and electric potential come directly from Coulomb's Law describing the force -- as in F=ma force -- between two charged particles.

    Calling volts a measure of electric force is like saying that height is a measure of gravitational force.
     
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  11. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    the little agitators bait the hook and we all fight to bite it!

    what is a volt? works here.
    what is a pound? would work somewhere else
    what is a gold standard? would set off the experts at yet another forum.

    I honestly believe half of these rudimentary questions are just clever trolling, since any 3 year old these days knows how to google such things. Yet, I often find myself leaping to answer such simple queries too. Just the nature of our basic personalities. We joined to help others gain understanding and are betrayed by our altruistic tendencies.
     
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  12. WBahn

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    Quite true. I don't know how much of it is trolling, since there seems to be no shortage of people that genuinely seem to not understand these concepts no matter how much Googling they do.
     
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  13. ian field

    Distinguished Member

    Oct 27, 2012
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    Some context would make that easier to answer.
     
  14. studiot

    AAC Fanatic!

    Nov 9, 2007
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    These questions come round with every generation of students.

    There are two different quantities measured in volts.

    Electric Potential (which is not potential energy by the way).

    and Electric Potential Difference, (which is what I think you are talking about).

    So which one do you wish to ask about?
     
  15. WBahn

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    Voltage is always a potential difference. When we talk about the voltage AT a point being a certain voltage, there is ALWAYS a reference point and the voltage is always the potential difference between that point and the reference point. In physics, that reference point may well be at an infinite distance, just as the reference level for gravitational potential is often take to be at an infinite distance. This is for conservative electric fields; for non-conservative fields you also have to specify the path between the two points.
     
  16. studiot

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    I have to disagree with you there.

    Consider a thought experiment in a universe with only one single electric charge.

    There is an electric field emanating from that charge in all directions.

    What units do you measure that field in?
     
  17. wayneh

    Expert

    Sep 9, 2010
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    I think you'd call it neutral and there would be no field.
     
  18. studiot

    AAC Fanatic!

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    Of course would be a field, that is electrostatics 101.

    I would think you will see a diagram of it in every EM textbook ever written
     
  19. WBahn

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    The electric field is measured in the same units as all electric fields, namely N/C. You can also express that in V/m. You cannot express the electric field in volts, since volts is not a measure of electric field.

    But let's leave the measurement of the electric field aside and take your claim that electric potential does not need to be relative to some reference. Okay, then if you say that the voltage at some distance from that charge is 100V, what does that mean? That's 100 joules/coulomb. What does that mean and why is it 100 joules/coulomb and not, say, 10 joules/coulomb or 1000 joules/coulomb. The answer is simple -- it is the net work that must be done on a unit test charge to bring it from rest at an infinite distance from your one single electric charge to rest at that point. And don't get hung up on the presence of a unit test charge in this universe that only has one single electric charge because the test charge does not have to physically exist, even in this imaginary universe, since it drops out of the integral and you are only integrating the electric field along that path.
     
  20. AnalogKid

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    Aug 1, 2013
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    If there is only one charged particle in the entire universe, there is no way to determine that it has a charge because there is nothing for that charge to interact with.

    ak
     
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