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lec06_ddn

# lec06_ddn - Lecture 6 Current Resistivity as a property of...

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9/11/11 2 Lecture 6 • Current Resistivity as a property of materials • Emf

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9/11/11 3 Electrostatics versus Electric Current
9/11/11 4 Electric Current Notice that flow of positive charge in one direction, + + + + + + + + + + CURRENT I Becomes more positive Becomes more negative It’s completely equivalent to negative charge in the opposite direction. CURRENT I Becomes more positive Becomes more negative - - - - - - - - - -

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9/11/11 5 Drift Velocity with without
9/11/11 6 Drift Speed, Total Charge & Current n = # charge carriers volume q = charge of each particle v d = drift velocity

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9/11/11 7 Relationship between Current and Drift Speed Find v d for 14-gauge copper wire carrying a current of 1 A. Assume there is 1 free electron/atom. n = n atoms = ρ N M Copper ρ = 8.93 g/cm 3 M = 63.55 g/mol 14 gauge wire Area = 2.081 mm 2 v d = I qnA
9/11/11 8 Electric Current one q in one q out

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9/11/11 9 Resistance Resistance is a property of the object, i.e . It depends on the shape and material
9/11/11 10 Resistivity I I length area A L Resistivity is a property of the material.

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9/11/11 12 Temperature Dependence

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