# EEE224_Fall10_SteadyCurrents - METU - NCC EEE 224...

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1 EEE 224 ELECTROMAGNETIC THEORY Steady Currents METU - NCC Assist. Prof. Dr. Özlem Özgün Office : S-144 Phone : 661 2972 E-mail : [email protected] Web : http://www.metu.edu.tr/~ozozgun/

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2 STEADY ELECTRIC CURRENTS Electrostatics is the study of charges at rest. Now, we shall allow the charges to move, but with a constant velocity (no time variation). steady electric current = direct current (DC) 0 = t
3 Types of Current Convection current (due to motion of electrons and/or ions in vacuum or gas) Conduction current (due to the drift of valence electrons in a conductive medium, such as metal wire) Separation of charge Æ creates electric force ( voltage, potential difference ) Motion of charge Æ creates electric flow ( current )

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4 Current - - One ampere is a number of electrons having a total charge of 1 C and moving through a given cross section in 1 s. Surface S dq I dt == = = Charge(C) coulombs (A) time(s) second
5 J (Amp/m 2 ) Current Density Vector S ds J J t J n J n t nt : normal(perpendicular) component : tangentialcomponent J J JJ J =+ ˆ ˆ : normal unit vector n n ds a ds a = ˆ n a Since J t is due to charges moving tangent to the surface element (they don’t cross the surface ds ), J t doesn’t contribute to the total current crossing the surface. Current through ds : ˆ .. nn d I J d sJ a d d s == = Current through S : . S IJ d s = flux of J Current & Current Density Vector

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6 Current & Current Density Vector If S is a closed surface: . S IJ d s = v Total current leaving (or entering) S Taken in outward (or inward) direction 00 vS dv ds ∇⋅ ⋅= = ∫∫ J=0 JJ v If J is solenoidal (or divergenceless) Divergence theorem
7 Types of Current (convection current) Convection current (due to motion of electrons and/or ions in vacuum or gas)

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## This note was uploaded on 01/07/2011 for the course EE 209 taught by Professor Alexander during the Spring '10 term at Middle East Technical University.

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EEE224_Fall10_SteadyCurrents - METU - NCC EEE 224...

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