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Unformatted text preview: Efield in different materials • Conductor • Insulator • Semiconductor Current and current density Current: dt dQ I = Current density: (assuming the current is perpendicular to dS) dS dI j = Relation between current and current density ∫ ⋅ = S S d j I t Convection current Convection current : u j v ρ = Conduction current: E j ⋅ = σ v ρ u E Can anyone tell the difference between convection and conduction current? σ is conductivity. Calculate drifting velocity in presence of Efield Convection current = conduction current u j v ρ = E ⋅ = σ E is the charge density of the medium. v E u ρ σ ⋅ = v ρ Different materials • Conductor: • Insulator (dielectrics): • Semiconductor 1 σ 1 << σ ? = σ Conductor Calculate resistance and conductance: S l R σ = Example • Calculate resistance of a thin film resistor Titanium D=1um L=1cm W=6um σ =1.8e6 s/m Example • Calculate resistance of a thin film resistor Titanium D=1um L=1cm W=6um σ =1.8e6 s/m Dielectrics...
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This note was uploaded on 03/30/2009 for the course ECE 335 taught by Professor Yifeili during the Fall '08 term at UMass Dartmouth.
 Fall '08
 YifeiLi
 Electromagnet

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