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lecture06

# lecture06 - II Electric current 1 Definition dQ I= dt Units...

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II. Electric current 1. Definition dt dQ I = Units: [ I ] = 1A = 1 C/s Conventional current Electron flow Example: 10 20 electrons passed through the electric conductor during 4 seconds. Find the electric current through this conductor. A s C t q I 4 4 ) 10 )( 10 6 . 1 ( 20 19 = × = = - C s A It q 5 . 0 ) 1 )( 5 . 0 ( = = = C s A It q 30 ) 60 )( 5 . 0 ( = = = Example: The electric current of 0.5 A is flowing through the electric conductor. a) What electric charge is passing through the conductor during each second? b) What electric charge will pass through the conductor during 1 minute? a) b)

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2. Current density dA dI J = Current density is a local characteristic defined at a point Current is not a local characteristic Current density is a vector directed along the current at a given point Current is a scalar Both current and current density are macroscopic characteristics Units: [ ] ( 29 s m C m A J 2 2 / 1 / 1 = = Current density J is a vector quantity whose magnitude J is the ratio of the magnitude of current dI flowing in a conductor to the cross-sectional area dA perpendicular to the current flow and whose direction points in the direction of the current.
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