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Lecture_09-1 - Lecture 9 1/16 Electric Current Q t dq dt...

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Lecture 9 1/16 Electric Current Current is charges in motion rate at which net positive charges move through a cross sectional area dt dq t Q I units of current is ampere (A) 1 A = 1 C/s Current is a scalar, signed quantity, whose sign corresponds to the direction of motion of net positive charges by convention A A d J I J is current density , a vector with units (A/m 2 )
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Lecture 9 2/16 Microscopic View of Electric Current in Conductor All charges move with some velocity v e A Random motion with high speeds (on the order of 10 6 m/s) but with a drift in a certain direction on average if E is present thermal energy scattering off each other, defects, ions, … drift velocity v d is order of magnitudes less than the actual velocity of charges
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Lecture 9 3/16 Current and Drift Velocity in Conductor drift velocity v d is order of magnitudes less than the actual velocity of charges t v A n q Q L A n q V n q Q d n is number density of charge carriers d d v A n q t t v A n q t Q I If we have: current (I) = 1.0 A copper n ~10 29 atoms/m 3 wire radius = 1 mm v d for copper ~ 0.01 mm/s
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Lecture 9 4/16 Ohm’s Law Current-Potential (I-V)
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