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Electronics Forum / Design / July 2008is it easier to negatively charge something than to positively charge it?
imagine a balloon floating in the air, and you give it a negative charge. This pumps more electrons into it (or onto its surafce). Giving it a positive charge (in relation to its suroundings) is done by removing existing negative electrons. Once all the electrons are gone, how could you possibly give it more "positive" charge? Whereas you can put as many electrons onto you want, limited only by the voltage of your charging source (and dielectric breakdown). The analogy I'm thinking of is a sealed metal tank. as long as you have a strong enough compressor, you can pressurize the tank to whatever PSI you want (until it ruptures of course). But the opposite case, of sucking the air out to create a vacuum, you will never be able to create less than about -15 PSI (I'm talking Gauge pressure, not absolute pressure, which just like VOLTAGE is measured in relation to the surrounding "ground" conditions). Does electric charge work the same way? >imagine a balloon floating in the air, and you give it a negative >charge. This pumps more electrons into it (or onto its surafce). [quoted text clipped - 13 lines] > >Does electric charge work the same way? Interesting. If you had, say, a ping-pong ball sized solid aluminum sphere, sucking all the electrons out scales to a voltage roughly in the 1e12 kind of turf. As a practical matter, it would come apart long before you could charge it that much. Atoms get ripped out of metals at much lower field strengths. And after all, it's electrons that hold things together. John > imagine a balloon floating in the air, and you give it a negative > charge. This pumps more electrons into it (or onto its surafce). [quoted text clipped - 13 lines] > > Does electric charge work the same way? Well, you could just as well give an object a positive charge by putting protons onto it, or positive ions. The difference is that the mass of a proton is much greater than -- about 1840 times -- the mass of an electron. You might also want to consider practical limits. A "pile" of electrons, or a "pile" of protons, will try mightily to get away from each other. I believe the capacitance of an electrically conducting sphere 1 meter radius in freespace is 111.3pF, more or less. So if you put a mere 1 coulomb of electrons on it (if you could actually do that), about 6*10^18 electrons, it will have a potential of nearly 9 billion volts. Left as an exercise for the reader: what's the electrical field strength immediately outside such a sphere? What keeps the excess electrons on the sphere? > Well, you could just as well give an object a positive charge by > putting protons onto it, or positive ions. The difference is that the > mass of a proton is much greater than -- about 1840 times -- the mass > of an electron. But protons don't like to hang around. Conservation of charge works, but physics being funny like it is, 13.6eV says those protons will grab up electrons, forming hydrogen which goes on its merry way, leaving the target electron-deficient. Depending on the material, some may chemically combine (I guess you could say a proton beam is the most acidic thing known to science, it's the ultimate Bronstead-Lowry proton donator), which you'd have to figure out in isolation of the charge. I suppose the way to tell would be to measure its mass extremely accurately, comparing equal charge (easy to measure) obtained by electron vs. proton bombardment. (Note that, at the charges we're talking, relativity will have a measurable effect. Assuming such apparatus that can actually measure these differences.) Tim  SignatureDeep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms > > Well, you could just as well give an object a positive charge by > > putting protons onto it, or positive ions. The difference is that the [quoted text clipped - 12 lines] > charges we're talking, relativity will have a measurable effect. Assuming > such apparatus that can actually measure these differences.) As has been pointed out earlier in this thread, you can't put much charge on a physical object before the mechanical forces generated by self-repulsion pull it apart. Thinking about protons as Bronstead- Lowry acids in this context is a pure waste of time. -- Bill Sloman, Nijmegen > As has been pointed out earlier in this thread, you can't put much > charge on a physical object before the mechanical forces generated by > self-repulsion pull it apart. Thinking about protons as Bronstead- > Lowry acids in this context is a pure waste of time. Well it was an aside, hence the parenthesis. You're welcome not to read it (which is what parenthesis mean). Tim SignatureDeep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms > imagine a balloon floating in the air, and you give it a negative > charge. This pumps more electrons into it (or onto its surafce). > Giving it a positive charge (in relation to its suroundings) is done > by removing existing negative electrons. Once all the electrons are > gone, how could you possibly give it more "positive" charge? Well, as the study says, the +ve or -ve charge depends on the lack of the electrons or excess of the electrons as compared to protons. So, for creating +ve or -ve charge in an object, all u have to do is jus disturb the electron-proton balance. Pump extra electrons for -ve charged object, and suck out some electrons to create a positively charged object!! ------ http://dharmanitech.blogspot.com Good answers, thanks everyone. |
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