Coulomb - count of particles or unit of charge ?

Discussion in 'Physics' started by RipClaw, Oct 9, 2008.

  1. RipClaw

    Thread Starter New Member

    Oct 9, 2008
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    I am a bit confused with what coulomb means.

    Does coulomb mean:
    A count of the number particles who lost their peace, and now known as charged.

    OR

    unit of charge itself & particle count does not matter.

    I am also confused with the following circular definition. :confused:
    Elementary Charge = 1.602176487(40) × 10^–19 coulombs
    Coulomb = 6.241 509 629 152 65 × 10^+18 elementary charges

    ωτ∫ ?

    What is the fun ? If you multiply them both, you get 1 :rolleyes:
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,137
    1,786
    The answer is that it is both. The definition is NOT circular, it is an equivalence relation. They are reciprocals of each other, and when we multiply reciprocals together we get, ceteris paribas, 1 !!
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    A Coulomb is a measure of charge as defined by the accumulation of 6.24 x 10^18 elementary charges. So the charge on that many electrons make up a Coulomb.
     
  4. RiJoRI

    Well-Known Member

    Aug 15, 2007
    536
    26
    Of course, this brings up the question, who counted those 6 1/4 bazillon charges??

    --Rich
     
  5. triggernum5

    Active Member

    May 4, 2008
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    Did Coulomb actually define that number, or was it derived later via charge/mass relationship of an electron, and the correlation of voltage and work/energy..
    Remember 1Watt = 1V*A = 1J/s = 1N*m/s, and we already had proper defined newtons, meters, seconds, and volts..
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    The name was chosen to honor Coulomb, not derived by him. It is the charge accumulated in one second by a current of one Ampere.
     
  7. triggernum5

    Active Member

    May 4, 2008
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    Didn't think Coulomb had the technology to pull that off..
     
  8. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    I've learned the elementary charge was first calculated by Robert Milikan in 1909 using a oil drops, a microscope, x-rays, and electrified plates. I still have not turned up the name of the person who counted the charges per second per amp, though.
     
  9. ZAIZAI

    New Member

    Oct 14, 2008
    3
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    The oil drop experiment is actually very neat. It is described in numerous text books, I am sure, Nuclear Physics by Irving Kaplan is one of them.

    Simple experiment together with some mindbogling theory (mathematics) and you kan figure out the charge of one electron...

    Yes everyone knows the charge is minus one, but prove it!
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
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    The charge on an electron is not divisible. As it is a unit charge, setting it equal to -1 is simply a matter of definition. No proof needed.
     
  11. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    It stems from the SI-definition of the Ampere:

    Ref. http://physics.nist.gov/Pubs/SP330/sp330.pdf

    This definition comes from work by André-Marie Ampère on his Force Law. Note that the Ampere is a base unit.

    We know from Millikan's experiment the value of the elementary charge. And Charles-Augustin de Coulomb defined the Coulomb to be:

    Or perhaps more logically in context of this discussion an ampere is one coulomb of charge going past a given point in the duration of one second.

    Therefore you can empirically arrive at the conclusion 1C = 6.24150962915265 x10^18 elementary charges.

    Dave
     
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