1Charles-Augustinde Coulomb(1736-1806)Lecture 2: Coulomb’s lawThis (and last) lecture, HRW, ch. 21For next time, HRW 22.1-22.5,22.8-22.92Last lecture•Coulomb’s Law: Interactions between charges•Uniformly charged spheresThis lecture•Charge is quantized and conserved.•In a conductor, electrons are free to move.•In an insulator, the motion of electrons is constrained.3•Charge is conserved:–Total charge at end is same as at beginning: Q1–Q2•Symmetry: Identical spheres–Final charge same on each•Charge on each sphere: (Q1–Q2)/2Example: charge conservation+Q1–Q2Connect the two spheres together with a metal (conducting) wire Interactive Lecture Question #2.1•What is the final charge distribution?Two identical metal spheres have charges +Q1and -Q24Rattling BallInduction separates the charge on the neutral middle ball. If it isn’t perfectly centered, it gets attracted to one side.+--++-+When the ball contacts the big sphere, it gets net charged.+.It is then repelled from that side, attracted to the other. The cycle repeats indefinitely if the charge on the spheres is always replenished.+-+
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