lecture01B - Charles-Augustin de Coulomb(1736-1806 Last...

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1 Charles-Augustin de Coulomb (1736-1806) Lecture 2: Coulomb’s law This (and last) lecture, HRW, ch. 21 For next time, HRW 22.1-22.5,22.8-22.9 2 Last lecture Coulomb’s Law : Interactions between charges Uniformly charged spheres This 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: Q 1 –Q 2 Symmetry: Identical spheres Final charge same on each Charge on each sphere: (Q 1 –Q 2 )/2 Example: charge conservation +Q 1 –Q 2 Connect 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 +Q 1 and -Q 2 4 Rattling Ball Induction 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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