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definition: voltage, current

Discussion in 'Electronic Basics' started by Paul Mars, Feb 14, 2005.

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  1. Paul Mars

    Paul Mars Guest

    I was trying to explain to a friend what they are and what the difference
    is. My schooling in Electronics was so long ago. I feel that I still have a
    very good grasp of what they are, but I could not explain them.

    My friend looked them up and got this:

    current (as in "electrical phenomenon") n. : a flow of electricity through a
    conductor; "the current was measured in amperes"
    voltage (as in "electrical phenomenon") n. : the rate at which energy is
    drawn from a source that produces a flow of electricity in a circuit;
    expressed in volts

    this is WRONG. Please help,
    p
     
  2. John Fields

    John Fields Guest

    ---
    We define current to be the number of electron equivalent charges
    moving past a fixed point in a specified interval of time, and we have
    named the unit of charge transfer the ampere, one ampere being equal
    to 6.24E18 electron equivalent charges moving past an arbitrary
    reference point in one second.

    We define voltage to be the force required to cause charge to move
    through/against a resistance, with one volt of force being defined as
    that force necessary to make 6.24E18 electron equivalent charges pass
    through a resistance of one ohm in one second.

    Since, then, a resistance of two ohms would require twice the force to
    cause a flow of charge equal to one ampere to occur, we can write:

    E 2V
    I = --- = ---- = 1A
    R 2R

    where I is the current, E is the voltage and R is the resistance.

    There's still a lot left to consider, the coulomb and the joule for
    example. Do you want to go on?
     
  3. Paul Mars

    Paul Mars Guest

    Please do and throw in the Watt please.

    BTW Your definition is more logical then what I learned. If you would like
    please comment on voltage being defined as the potential difference between
    two points period.
     
  4. Ratch

    Ratch Guest

    Charge exists in two flavors, positive and negative. When it moves, as
    the negative electrons in a wire, or positive or negative ions in
    electrochemistry, it is called a current. It takes energy to move charges
    from on place to another. The amount of energy per unit charge is voltage.
    If it takes 5 joules of energy to bring 1 coulomb of charge from point A to
    point B, then the voltage of point B with respect to point A will be -5
    volts. Think of voltage as the amount of energy per unit charge, not force.
    Voltage does produce a electrostatic field which repels or attracts a unit
    charge with a finite force, but voltage by itself is not force. Wattage is
    simply energy transferred per unit of time. Any good electrical text will
    describe what I wrote in more detail. Ratch
     
  5. Yes!

    I was going to quibble with force on this one, but you done the job fine
    Ratch:)

    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
  6. Genome

    Genome Guest

    Indeedy, sort of. The Ampere was/is defined as 1 Coulombe per second of
    charge passing by.

    It has something to do with electrochemistry and deposition of a Molseworth
    of Avogadros somesuch somewhere else.

    mole junior ask brane, 'if you are so clev wot is one plus one?' at which
    point brane larf so much it burst into a trillion pieces.

    The charge on an electeron is 1.6019dribblydribblyE-19 Coulombes. Multiply
    that by Johns number of electerons and you get 1...ish.

    The charge on an electeron was worked out by Millikan (sp)

    Blame the Chemists.

    DNA
     
  7. John Fields

    John Fields Guest

     
  8. Genome

    Genome Guest

    No......! I shit you not.

    The bloke was an American.

    He went and suspended droplets of something that he charged up in an
    electric field (no pun intended) and measured something versus something
    like gravity or another thing (how fast it went up and down) and it was dead
    sensitive and they all came out to be multiples of the charge on an
    electeron and he found the smallest one was 1.6-19C or something.

    It was a classic experiment.

    DNA
     
  9. John Fields

    John Fields Guest

    ---
    Milli = 1 times ten to the minus three so Millikan, with a name like
    that, should have only been able to measure to one part in a thousand.

    However, his exquisite experiment yielded results sixteen orders of
    magnitude greater than one part in 1000, so if his surname would have
    been Attodecikan, it would have fit his accomplishment. :)
     
  10. BobG

    BobG Guest

    Has the OP given his friend the hydralogical analogy yet? Volts is PSI
    in the hose and Amps is gallons per minute, the size of the hose is the
    resistance of the wire. Seems intuitive.
     
  11. Genome

    Genome Guest

    Thanks for explanation.

    No offence meant to you or owners thereoff.

    DNA
     
  12. Genome

    Genome Guest

    Monster,

    "Millikan first let them fall until they reached terminal velocity. Using
    the microscope, he measured their terminal velocity, and by use of a
    formula, calculated the mass of each oil drop."

    But..... I think that's wrong.

    DNA
     
  13. Pig Bladder

    Pig Bladder Guest

    This last election, I heard that the electerons were charging
    five bucks a vote!
     
  14. Rich Grise

    Rich Grise Guest

    Voltage is defined as the potential difference between two points. The
    "period" is a punctuation mark.

    Potential is like pressure.

    When you compress a spring, you give it potential energy, which it
    stores up in the form of the stress on the spring itself. When you
    release the spring, that energy is released as "kinetic energy", but
    that's another topic.

    The point is, that "potential" corresponds to "pressure." It's
    something like water flowing downhill, where the "potential energy" is
    represented by the height of the water column - actually, the height is
    the voltage - the current, obviously, is the flow, and the power is
    the pressure times the flow.

    Now, if you just let the water fall, then the analogy to an electronic
    circuit kind of breaks down, except that a waterfall might be kind of
    conceptually like an arc.

    But if it falls through a waterwheel, then you can extract energy from
    it. The amount of energy you can extract at any given moment can be
    expressed as (or derived from?) the flow rate multiplied by the pressure
    difference. No, wait - rate - that's the rate at which you're extracting
    energy. Energy and work are almost interchangeable - I had a physics
    teacher who said, "Energy is the capacity to do work." Work, of course, is
    force times distance. And power is the rate of doing work.

    Hope This Helps!
    Rich
     
  15. Ratch

    Ratch Guest

    No it is not defined that way. It is often confusingly described that
    way. Potiential of what?
    In what way? Force per unit area vs energy per coulomb!?
    No potential energy is converted into kinetic energy unless you propel
    something like a pinball. It could just as easily be converted into heat by
    connecting it to a dashpot.
    Does the above description help anyone to really understand what
    voltage is? Ratch
     
  16. Fred Abse

    Fred Abse Guest

    Stephen Leacock?
     
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