EEE224_Fall09_MaterialMedia

EEE224_Fall09_MaterialMedia - METU - NCC EEE 224...

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1 EEE 224 ELECTROMAGNETIC THEORY Static Electric Field in Material Media METU - NCC
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2 What about electrostatic fields in a material media ? So far, we considered electrostatic fields in free space (or vacuum). Material Media Material classification: Conductors Dielectrics (or insulators) Semiconductors (in between the two)
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3 Material Media (a) The conductor exhibits no energy gap between the valence and conduction bands. (b) The insulator shows a large energy gap. (c) The semiconductor has only a small energy gap.
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4 σ : conductivity (Siemens/m) If σ >> 1, good conductor (e.g., metals) Charges flow easily. If σ << 1, good insulator Almost no charge flows.
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5 Static Electric Fields in Conductors FACT 1 : In electrostatics, electric field E=0 inside conductors . E e : Electric field before the conductor was introduced. E i : Electric field created inside the conductor as a reaction to E e . E : Resultant electric field after the transient period following the insertion of conduction object. E i = -E e Î E = E i + E e = 0 inside the conductor
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6 Static Electric Fields in Conductors FACT 2 : Electric field E is always perpendicular (normal) to the surface of a conductor . (Its tangential component is zero) 0 E ∇× = 0 C Ed l = ± 0 (as h Î 0) 0 (as h Î 0) 0 (as E=0)
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7 Static Electric Fields in Conductors FACT 3 : The normal component of E-field is: 0 enclosed S Q Ed s ε ⋅= ± 0 enclosed top bottom sides Q ++ = ∫∫ ρ s : surface charge density 0 (as h Î 0) 0 (as E=0) 0 s n s Es ρ Δ Δ= 0 s n E = 0 s n E =
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8 Static Electric Fields in Conductors FACT 4 : The conductor is an equipotential surface.
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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_Fall09_MaterialMedia - METU - NCC EEE 224...

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