EEE224_Fall10_Electrostatics

# EEE224_Fall10_Electrostatics - METU NCC EEE 224...

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1 EEE 224 ELECTROMAGNETIC THEORY OVERVIEW of ELECTROSTATICS 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 WHERE ARE WE? EEE 224 Electrostatics : charges are at rest (no time- variation) Steady electric currents : charges are in steady-motion (no time-variation) Magnetostatics : charges are in steady- motion (no time-variation) Electrodynamics : charges are in time- varying motion (give rise to waves that propagate and carry energy and information) EEE 303 (static) 0 = t 0 t (dynamic) Electromagnetics is the study of CHARGES at rest in motion
3 Electrostatics Electrostatics is a branch of electromagnetics dealing with the effects of charges at rest . Electric fields do not change with time. Simplest situation in electromagnetics, but fundamental to the understanding of more complex models. Oscilloscopes, ink-jet printers etc. are based on electrostatics.

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4 Electric Field Intensity Electric field intensity is the force per unit charge that a very small stationary test charge experinces when it is placed in a region where an electric field exists. Unit : (Newton / coulomb) or (Volt / meter) q F : force experienced by the charge q in an electric field.
5 Fundamental Postulates of Electrostatics : volume charge density (coul / m 3 ) in free space (or in vacuum) : permittivity of free-space 0 v E ρ ε ∇⋅ = 0 E ×= v 0 Thus, static electric fields are always irrotational. static electric fields are not solenoidal unless v =0

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6 Fundamental Postulates in Integral Form 0 total S Q Ed s ε ⋅= v 0 E ∇× = V S Q total ds . 0 v E ρ ∇⋅ = () total enclosed v V Qd v = where Gauss’ Law Take volume integral and apply Divergence thm. S C 0 C l = v Take surface integral and apply Stoke’s thm.
7 Gauss’ Law 0 total S Q Ed s ε ⋅= v V S Q total ds . total v V Qd v ρ = where Gauss’ Law is useful in “symmetry conditions ”, such that the normal component of the electric field intensity is constant over an enclosed surface. In such cases, the surface integral is very easy to evaluate. A “Gaussian surface is a surface to which the electric field intensity is normal and over which equal to a constant value.

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8 Gauss’ Law Cylindrical symmetry ”: (rotational symmetry, axial symmetry) Everything is the same around its vertical axis.
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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_Electrostatics - METU NCC EEE 224...

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