Lecture+11+feb9 - Lecture 11 EMF, Energy, and Power in DC...

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Lecture 11 EMF, Energy, and Power in DC circuits
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Microscopic view of metal conduction “Free” Electrons in a metal are highly scattering---their net displacement is very small compared to the distance traveled. They DRIFT slowly to right against E. The drift speed is so low that it might take a day to get across our lecture hall! Let’s see why.
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- - - - - - - A - - - - - - - - - - - - - - - v d dt e drift Shaded volume has dQ dQ = q N e dQ = qndV = qnAv d dt Where “n” is free electron density I = dQ/dt = qnv d A J = I/A = qnv d n is huge! ~10 29 electrons/m 3 Hence nq ~ 10 10 C/m 3 The concept of electron drift velocity in section 25.1 is important. The theory of metallic conduction in 25.6 should be read to give more physical meaning to this, but I’m not as concerned about the details in 25.6 Electron drift velocity (Average velocity of all conduction electrons)
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ΔV(=V R ) for current-carrying Resistors The “IR Drop” E points to lower V I and E point in same direction + terminal of battery is higher V than - terminal + V - I E R V R drops by IR in direction of I
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Lecture+11+feb9 - Lecture 11 EMF, Energy, and Power in DC...

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