Lecture9_SP10 - Topics to be covered in class: Review:...

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Topics to be covered in class: Review: dielectric inside a capacitor Resistivity, conductivity, resistance Ohms’s Law Review: upcoming mid-term Independent reading: (a) temperature dependence of the resistance (pp.870-871)
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How does the capacitance change after a partially-filling dielectric is inserted?
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How does the capacitance change after a partially-filling dielectric is inserted?
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Said differently: the battery was disconnected BEFORE the dielectric was pulled out!
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Dielectric is pulled into a capacitor by fringe electric fields: that’s why the energy of the capacitor went up! Dielectric did not want to come out, we had to pull it out: we’ve done POSITIVE work (work at our expense)! Electric field did NEGATIVE work Æ its potential energy went up! Potential energy would have gone down had the E-field done POSITIVE work (work at the E-field’s expense!)
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Conundrum: you labor and labor – and where’s the fruits??
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Let’s become accountants: where is our work going??
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Let’s become accountants: where is our work going??
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Would you do more or less work if you just yanked the dielectric out??
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Lecture9_SP10 - Topics to be covered in class: Review:...

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