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Could someone explain charge to me?

  1. Apr 13, 2004 #1
    What exactly is charge?

    I am currently in both Physics 12 and Chemistry 12 and we just started Electrostatics today and I got very confused.

    Sure, I could just accept it for being and plug whatever I need to into the equation to get my answer but I'd prefer to know exactly what's happening.

    I thought that perhaps they are ions in the chemical sense or are they perhaps electrons and if so how are they being removed from the valance shells by just rubbing?

    I'm a little confused... could someone help me with an explanation?

    Thank you,

    Marc
     
  2. jcsd
  3. Apr 13, 2004 #2

    Janitor

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    The answer depends on the context. In hot plasmas, charged particles are electrons and positive ions. If the plasma is hot enough, most of the nuclei are entirely stripped of their electrons.

    As you point out, in an electrolyte solution, charges are ions, being atoms or molecules containing an excess or a deficit of electrons.

    In a copper wire, the charges of importance are valence electrons, I believe.

    In a semiconductor, there are electrons in conducting bands, and when an electron is kicked from a filled band to an empty band, a hole is left behind in the previously filled band. The hole can act as a positive charge; there is an interesting discussion on this in another thread.

    In a charged capacitor, one plate has an excess of electrons, while the other plate has a deficit of electrons.

    Inside of baryons and mesons there are quarks, which have a charge magnitude of 1/3 or 2/3 the magnitude of the electron charge. For reasons having to do with the nature of the force binding quarks together, you never come across bare quarks under ordinary circumstances.

    I hope this wasn't entirely stuff you already knew.
     
  4. Apr 13, 2004 #3
    Well, no, I didn't know the majority of that.

    Let me give you a context then. For instance, a bolt of lightening, what causes the charge separation in the clouds? It is perhaps because of the dipole interactions between the water molecules that push the negative ones to the bottom to the point that ... well.. *shrugs* I don't know exactly what lightening is.

    I'm aware that it changes based on situation. Sorry I didn't make it clear... I am thinking more of common everyday charge. For instance, when I take a sweater off... what causes that charge? Where does it come from? The rubbing of the material... but what creates that charge? Does it come from something in the air? Is it stripping atoms in the air of their electrons that creates the small spark that we see?

    We were analyzing the whole "Induction, contact, and friction" charging and I was confused as to what the charge was doing on the ball or rod in the first place?

    Also, what causes the charge on a charged object to disappear with time? Is it just a variety of interactions with the air? Filling of valence shells or... that's the only one I can really think of...

    Thanks for the quick response!

    *confused*
     
  5. Apr 13, 2004 #4

    Janitor

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    Here is a link on van de Graaf generators that may help:

    http://www.amasci.com/emotor/vdg.html

    I have read that the generation of lightning in thunderstorms is along the same lines as the way it is done by a van de Graaf generator. Whether that is a sloppy or a realistic thing to say, I'm not sure.

    I have also heard that dust in the air is important in causing lightning. However, Jupiter has lightning storms, and since it does not have a solid surface (at least not anywhere close to the cloud tops that our spacecraft can photograph with their cameras) with the clay needed as a source for dust, I suspect raindrops (which Jupiter does have) are critical to lightning generation.
     
  6. Apr 14, 2004 #5
    may be charge is just like mass a fundamental quantity that cannot be described
     
  7. Apr 14, 2004 #6

    Chi Meson

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    NOt, "may be," but "is."

    Janitor's comments are all fine; thi sis just my 2 cents (did anyone else notice that the "cent" symbol is gone?)

    THere is the quark model of sub-atomic particles which is very accurate at predicting the charge and mass (and other fundamental properties) of the many hundred "fundamental particles." BUt this model does not explain what "charge" is.

    THe latest conjectures, such as string theory (which is not a true "theory" because it can't be tested) delve into what "charge" and "mass" actually are. Untill we know what is underneath, we have to accept that there is a base-layer of "what is." Currently that base begins with these fundamental properties.

    Charge, therefore, is a quality of matter that causes certain effects (that's what you're learning now). There is lots of evidence that shows that no particle can have a total charge that is not a full-integer multiple of the fundamental charge (the charge of one electron or proton).

    [No, the quark is not a "particle" because no single quark can exist on its own; but yes, some quarks carry fractions of the fundamental charge. That debate is over sematics.]

    Charge comes in two "flavors" that where dubbed "positive" and "negative" by Ben Franklin; although they show "opposite" natures, there is nothing intrisically positive nor negative about charge.

    THe Law of Conservation of Electric Charge is one of the strongest laws of physics. Basically it says that no charge can be created or destroyed, ever. So when you "charge" something, you are by law, also chrging something else equally and oppositely. Scuff your feet on the carpet, and you get charged negatively by stealing some electrons from the carpet. This means that the carpet has been positively charged since it now is missing some electrons.

    Oh, I could go on...
     
  8. Apr 14, 2004 #7

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    Since the topic of lightning came up.

    I remember as a kid looking at a book about a volcano called Paricutin, in Mexico. It started as a crack that opened up in a farmer's field in 1943. It got to be fairly big, erupting on and off over the course of a decade. Nobody was killed by ashfall or lava flow, but three people were killed by lightning generated by the plume of ash rising into the sky. It seems that small solid or liquid grains/drops moving through air lead to a charge buildup. I have sometimes gotten quite a shock from handling a vacuum cleaner hose while suctioning up dust from the garage floor.

    http://volcano.und.nodak.edu/vwdocs/volc_images/img_paricutin.html
     
  9. Apr 14, 2004 #8
    is charge quantised?
     
  10. Apr 16, 2004 #9

    Chi Meson

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    Yes.

    It is a well-supported theory that no PARTICLE can have an electric charge that is not a full integer multiple of the fundamental charge (1.60217646263 x 10^-19 Coulombs).

    The theorized charge of individual "quarks" will be 1/3 or 2/3 of this amount, but since individulal quarks do not exist on their own, then the previous paragraph is so far still valid.

    This is essentially what is meant by "quanta." Specific, "discreet" packages of a certain quantity.
     
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