Unformatted text preview: C ab for a 6 = b are called, at least by some, electrostatic induction coeﬃcients. They depend only on the shape of the conductors (and dielectrics, if present). a) Argue that C ab = C ba and that C aa > 0. Hint: write down the energy in terms of the C ab . b) In the gaussian system, what are the units for C ab ? What is C for a sphere? c) The Earth is a good conductor and approximately spherical. What is the capacitance of the Earth in “practical” units (microfarads)? If we remove all the electrons out of a gram or so of material on the Earth, what would be the potential of the Earth? What would be the electric ﬁeld on the Earth’s surface (in volts/cm)? Hint: you can ﬁnd conversion factors for electromagnetic quantities on the back cover of textbooks. Google can probably do it too). Hint 2: I’m looking only for rough numbers here....
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 Spring '11
 Bedaque
 Charge, Work, capacitances, concentric conducting spheres, ELECTRODYNAMICS PROBLEM SET, nondiagonal constants Cab

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