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Volts vs Electron Volts

  1. Apr 22, 2006 #1

    Bear with me, I'm a mature student returning to the sciences after a 16 year break...

    I'm currently reading up on electricity and cannot, for the life of me, get my head around what 'appears' to be an inconsistency. Obviously my brain isn't 'seeing' the answer properly just yet so I could do with some help.

    Basically, if one coulomb has 6.25 x 10 -18 electrons and 1 volt is the potential energy required to carry out 1 Joule of work how is it that 1 eV is only worth 1.602 x 10. -19 Joules??? Why not 6.25 X 10 -18 Joules?

    I've read around many sites but can't get my brain to shift into the right perspective with this...

  2. jcsd
  3. Apr 22, 2006 #2
    A electronvolt is the kinetic energy a electron gets when its passed through a 1 volt electrostatic potential difference.

    I dont quite follow why you think that ammount of energy in relation to a joule should be the same as a electrons charge in relation to a coulomb??
    Last edited: Apr 22, 2006
  4. Apr 22, 2006 #3


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    By the way your exponent is off. 6.25 x 1018 electrons make up one coulomb of charge.
  5. Apr 22, 2006 #4
    Ok, this is where I am going wrong obviously. The problem is I need to be un-confused...
  6. Apr 22, 2006 #5
    Quite right, apologies for the typo.
  7. Apr 22, 2006 #6

    Physics Monkey

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    A volt is one joule/coulomb. The charge of an electron is - 1.6 x 10^-19 coulombs. The energy acquired by one electron being accelerated through a potential difference of one volt is therefore (1 volt) x (1.6 x 10^-19 coulombs) = 1.6 x 10^-19 joules. Thus one electron volt, one eV, is 1.6 x 10^-19 joules.

    Hope this helps.
  8. Apr 22, 2006 #7


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    you're on the right track. you were asking the right question in your initial post. so now ask yourself: what is the reciprocal of 6.25 x 1018 electrons/coulomb?
  9. Apr 23, 2006 #8
    rbj wins a big fat cigar :smile:

    It's nice when the obvious strikes you in the face :rofl:

  10. Apr 23, 2006 #9
    I think you are confused with the extra negative power, i.e from 18 to -19.

    the reason is 1 divided by 6.25 gives 0.1602, and writing that in standard form gives 1.602 x 10^-1, giving you an extra negative power, so the charge is not 1.602 x 10^-18 but 1.602 x 10. -19 .
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