When a positively-charged rod is brought near a neutral insulated metal sphere, the electrons on the sphere will be attracted to the side of the sphere that is near the rod, leaving protons on the other side of the sphere away from the rod. Since protons cannot move, how do we explain this phenomenon?
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$\begingroup$ the protons do not move from their lattice location. Read this en.wikipedia.org/wiki/Electron_hole $\endgroup$– anna vCommented Mar 26, 2023 at 9:09
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2 Answers
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. . . . . leaving protons on the other side of the sphere away from the rod. is a misleading statement.
A metal cam be through of as made up of positive ions, eg $\rm Cu^+$, fixed in space (lattice) and a "sea" of free/mobile electrons not influenced by any particular positive ion.
When an electric field is applied, eg due to a charged rod being close to the metal, free electrons migrate leaving one side of the metal with fewer free electrons per unit volume (positive side) and the other side of the metal with more free electrons per unit volume (negative side).
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$\begingroup$ Hi Farcher, thank you for your response. Is it wrong to say that the protons get repelled to the right side of the sphere? The textbook that I referred to shows positive charges only on the right side. $\endgroup$– LeenCommented Mar 27, 2023 at 0:31
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$\begingroup$ @Leen that's an incorrect statement, yes. The electrons move, but the protons (aka atoms) don't, since they are locked in place by the lattice. $\endgroup$– AllureCommented Mar 27, 2023 at 0:52
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$\begingroup$ @Leen Your textbook is showing the net charge. There are actually nuclei and electrons everywhere. The charge is, in practice, only slightly out of balance. $\endgroup$ Commented Mar 27, 2023 at 1:05
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A metaphor to supplement the correct answer by Farcher.
Imagine you took a sheet cake with icing, and scraped all of the icing off of left side to satisfy a picky eater who doesn't care for buttercream. If you have another eater who loves cake icing, you might pile the icing on the right side. Now your cake is polarized.
If someone who doesn't mangle their cakes were to see this monstrosity, they might ask why there is just cake on the left side. Of course the cake goes all the way across, and there is an icing deficit on the left side rather than a cake excess.
For a multi-electron atom like copper or aluminum, imagine the ion lattice as a layer cake, where only the icing on the top of the cake is mobile.
