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How is charge born?

  1. Jul 24, 2006 #1

    I understand that an electric field is created as a result of the force between two opposite charges.

    But how is a chrage initially created?

    Supposing I have two parallel metal plates acting as a capacitor - they become charged when I apply an electric field across them i.e C = Q/V but how is the electric field created in the first place .... more charges???

    Please help!


  2. jcsd
  3. Jul 24, 2006 #2
    you got it backwards im afraid, the electric field inside the capacitor is a result of the charges on it's plates...

    when you connect a power source (e.g. battery) to a capacitor, electrons start moving from one plate to the other - until the voltage on the capacitor is equal in size to the voltage of the power source.
    you don't make charges... you just drive them around.

    a charge cannot be created, the total charge is a constant quantity in our universe

    electric field can be viewed as a field that exist around a charge, you can calculate it by measuring the force on another charge, but that's not it's definition...
    Last edited: Jul 24, 2006
  4. Jul 24, 2006 #3
    Hi Fargoth,

    Sorry for the confussion! I realise that the electric field in a capacitor is due to the charges on its plates.

    However, what I should have said is how does that charge come to be on its plates? The electric field I was referring to, when I said

    Was the electric field generated by a capacitance meter used in measuing the capacitance of these plates.

    To make clearer, how do the plates become charged - sorry for such ramblings!


  5. Jul 24, 2006 #4
    sorry, i posted and then re-edited my post to mkae it more informative, try looking your answer on my initial post, and if you didn't find it yet, ask again, and i'll answer in more length.
  6. Jul 24, 2006 #5
    No that explaination is fine!

    So any material has a charge i.e contains molecules with a number of protons and electrons have a positive and negative charge respectively. So if I were to make these hypothetical plates from a material with a high proton count then they would have a larger positive charge and thus a better capacitance than plates made from a low proton weighted material, thus a poorer capacitor?

    So your statement that the charge is a constant through out the universe comes from the fact that the universes material is finite and therefore contains a finite number of protons and electrons. We then can put these atoms togother to create molecules. When we place one molecule 'near' another then a electric field is created proportional to their charges and inversely proportional to their separation. :rolleyes:

  7. Jul 24, 2006 #6
    well, the capacitance is measured by the quantity of charge you can displace between it's two plates per the voltage between these plates.

    there is of course a finite charge that can be displaced, because there is a finite number on protons and electrons on the plates, and there are even less electrons that are on the conduction band - so the normal linear equation you know only holds for "small" voltages.

    but as long as you refer to this equation, it doesn't matter what matterial you used, as long as it's a conductor, you can get you capacitance higher by putting some polar molecules between the plates, so they re-arrange against the field and reduce the voltage per charge displaced between the capacitor plates.

    as for the second remark, there are more then protons and electrons.
    a proton can be transfomed to other particles - but they must have a total of one positive electron charge.
    and a neutron might decay into a proton and an electron but the total charge is still zero.
  8. Jul 25, 2006 #7
    how is charge created at the first place?
  9. Jul 25, 2006 #8
    How is logic created?
  10. Jul 25, 2006 #9

    Andrew Mason

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    If you can answer that question or "how is mass created?" I can guarantee you the Nobel prize in physics.

  11. Jul 25, 2006 #10
    mass is energy which is neither destroyed, nor created, if you are asking me how to convert from energy to mass, I guess that would give me something more than nobel prize.
  12. Jul 25, 2006 #11


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    It was never created.

    Try wrapping your brain around that
  13. Jul 25, 2006 #12
    ok, what are its subatomic particles?
  14. Jul 26, 2006 #13


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  15. Jul 26, 2006 #14
    you can't create a charge from thin air (im not talking about both positive and negative - thats happening all the time, just one of them)

    i don't think that ever happened, even in the beginning of the universe, the universe always was electrically neutral, there was a time in which the negative and positive charges haven't formed atoms yet - and photons were constantly being absorbed, but the universe was still neutral as a whole.
  16. Jul 26, 2006 #15

    Charges are everywhere around us. Materials are made of atoms full with electrons.

    The electric charges around us may have very different "mobilities".
    Deep electrons in atoms may need an x-ray or a gamma-ray to be separated from their atom.

    Free electrons in metals (also called conduction electrons), on the contrary, are very free to move from one atom in the metal to another. They could even leave the metal with a little energy, but the positive charge they leave behind will attract them back if the energy is too low. Even non-metallic substances can leave electrons rather easily, like barium or calcium oxides in electronic tubes. This is also how thermocouples create a small but measurable voltage when heated: the two metals in the junction have different attractiveness for electrons and electron choose their side.

    Besides, there are many different ways to drive electric charges into motion.
    The oldest known method is friction (see Van de Graaff).
    The most used drive is the electromotive force created by magnetic induction.
    Radioactivity could be used since energetic radiation can quick off electrons (the photomultiplier for example)

    Chemistry offers many other possibilities. Electrons may have more affinity for one substance and will move if they are given to opportunity to do so. (this is how batteries work).

    In the end, it may happen that the preferred location for electrons are on the plates on your capacitor. They may prefer to leave the battery, at least as far as this is possible: an electrical equilibrium will stop the flow at some time (when the capacitor is charged at the potential of the battery).

    So, charges are no mystery at all. Like anything here on earth it can move, it can be moved, can be manipulated.

    Last edited: Jul 26, 2006
  17. Jul 26, 2006 #16
    Does charge have any subatomic particles or is it energy?(no mass)
  18. Jul 27, 2006 #17
    I thought I heard somewhere that all charged particles have mass, but that not all mass particles have charge.
    Could be wrong, though, I'm no expert and can't remember the source or its validity.
  19. Aug 4, 2006 #18
    Why do charges accumulate at the edges of objects i.e ones fingers (the spikey parts of the body to get electrostatic shocks) or the edges of the capacitors plates?
  20. Aug 5, 2006 #19
    A nullified universe of alocal fluctuations.
  21. Aug 5, 2006 #20

    Please could you elaborate more on this?

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