L24_a - ELECTRIC CURRENT FLOWING CHARGE (Quick Review from...

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Unformatted text preview: ELECTRIC CURRENT FLOWING CHARGE (Quick Review from Chap 21) CURRENT: rate at which charge crosses a specified surface amount of charge per unit time surface (for example) could be cross-section of a wire symbol for current is I Average current is t Q I = ave Q is amount of charge across surface in time t DIRECTION OF CURRENT: SAME as direction of POSITIVE charges crossing surface OPPOSITE direction of NEGATIVE charges crossing surface + +-- Current (I) INSTANTANEOUS CURRENT (which we will just call current) dt dQ I I t = = ave lim Units of current are Amperes: 1 A = 1 Coulomb per second CHARGE CARRIERS DEPENDS ON MATERIAL In good conductors (metals): current carried by electrons (negative) o Direction of electron motion opposite to direction of current flow I (current) -e -e -e -e -e conductor In plasma (ionized gas) or electrolyte (i.e. solution in batteries) o current flow can be carried by: positive ions (moving in direction of current flow) negative ions (moving opposite to current flow) In semiconductors (i.e. in transistors, computer circuits, etc.) o current flow can be carried by: electrons (negative) moving in direction opposite to current flow positive charge carriers (holes) moving in direction of current flow-- + + I (current) + + + + + -- -- -- Material with positive and negative charge carriers (i.e. plasma, electrolyte, or semiconductor) MICROSCOPIC PICTURE:...
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This note was uploaded on 03/08/2012 for the course PHYSICS 1051 taught by Professor Michaelmorrow during the Winter '12 term at Memorial University.

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L24_a - ELECTRIC CURRENT FLOWING CHARGE (Quick Review from...

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