The book i am reading says that if an object is negativeley chargedit has more e

Question

The book i am reading says that if an object is negativeley chargedit has more electrons than protons and if it it positevely chargedit has lost electrons and thus has more protons. In the nextsection on gausian surfaces it says that if there is no net chargein the interior of a conductor then all the excess charge in aconductor resides on the exterioir. What i am confused about is bythe books definition the excess of charge implies that there is anet charge because there are more protons or electrons depending onwhether or not the charge is positive or negative, so how is itthat the net charge is zero.

Explanation / Answer

Since all charges can move in perfect conductors and anyexcess charge will end up at the surface, it therefore atfirst seems odd that your book would give an exception to the caseof having a net internal charge. Let me expain this exceptionfirst. Even a perfect conductor can have a non-conducting lump ofcharge (the charge is fixed) placed somewhere inside ofit - this would draw charge to this lump creating a blanket ofsurrounding charge opposite to the charge in the lump.Also the same charge as the lump will appear at the outeredge of the surface of the conductor -to keep the conductorover all neutral. What all this means is thatcharge in this situation will beinside the perfect conductor -there wouldbe a net internal charge. As an example you could imbed a coulumb of charge anywhereinside any conducting solid and a negative coulumb of charge wouldsurround the imbedded coulumb drawing off a coulumb of charge fromthe surface of the conductor. Therefore there can be a net charge inside a perfectconductor, since the "lump" is not part of the conductor, ifsay a lump of plastic (an insulator) with trappedcharge is placed anywhere inside the conductor. Normally though excess charge placed anywhere in or on anyconductor will have liked charged particles that will repelfrom each other (since they are not trapped) until all chargeis jambed onto the suface- where although the charges may notbe farthest way from one another ( a few charges internally wouldgreatly spread out the charge at the surface increasing averagedistance apart) but at least they are "stable" since all thecharges will always feel an outward push only stopped by runningout of conductor and jambing against an insulator at thesurface then evenly coating the surface in charge (usually airis the insulator). This is why there is no net internalcharge since any charged particle in excess thatmoves into the interior of the conductor will be quiklypushed in "some" direction until it (or another likedcharge) very quickly jambs up against the surface againleaving the inside on aveage with no net charge. I thought I would explain why there is only charge at thesurface of a conductor since I think this is the essence ofyour confusion. Therefore in the normal case with no imbeddedfixed charge there will be a netsurface charge but no netinternal charge. It is very important to point out that in the special but veryimporant first case there is anet charge inside the conductor its self and anyexcess charge added to the conductor can be inside theconductor -this is the case your book was tryingto "cover" if not fully eplain at that moment. Alsoit can be still said that all net charge is suface chargesince the internal charge in the first case resides on the surfacesurrounding the internal "lump" of fixed charge -but it is still anet charge inside the conductor.

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