EE2011 Lecture 3 - Electrostatics Parrt II

I r l j ds e ds s s prof joshua le wei li em research

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ctance dl dl V 1 A l l R ;G . I R l J ds E ds S S Prof Joshua Le-Wei Li, EM Research Group Prof 7 EE2011: Engineering Electromagnetics Electromagnetics Conductors • Example 3 Question: The radii of the inner and outer conductors of a coaxial cable of length l are a and b, respectively. The insulation material has a conductivity . Obtain an expression for G’, the conductance per unit length of the insulation layer. Solution: The total current of I, will be flowing through the area of A=2 rl. Therefore, we have the current density J and electric field E as follows: J I I I ˆ ˆ ˆ Jr r r . ; so E 2 rl Aa 2 rl a ˆ Ir I b ˆ dr E dl r Vab ln . a 2 lr 2l b b Therefore, the conductance per unit length is G1 I 2 G' . b l Rl Vab l ln a Prof Joshua Le-Wei Li, EM Research Group Prof 8 EE2011: Engineering Electromagnetics Electromagnetics Conductors • Joule’s Law – Power dissipated in a conducting medium in the presence of an electrostatic field E is considered. The electron and hole charges are qe ve v and qh The electric force acting on qe and qh are Fe vh qe E vh ve v, respectively. E v and Fh qh E E v. The work (energy) expended by the electric field by the electric field is W Fe l e Fh lh le lh W Fe Fh Fe u e Fh u h t t t E J v where the electron shift velocity is u e P velocity is u h ve E ue vh E uh v l e / t , while the hole shift l h / t. Prof Joshua Le-Wei Li, EM Research Group Prof 9 EE2011: Engineering Electromagnetics Electromagnetics Conductors • Joule’s Law - Continued – Power dissipated in a conducting medium is P E Jdv (W) - Joule' s Law V 2 E dv V E x ds E x dl S E x A E xl Prof Joshua Le-Wei Li, EM Research Group Prof IV 10 l I 2 R (W). EE2011: Engineering Electromagnetics Electromagnetics Conductors • Example 4 Prof Joshua Le-Wei Li, EM Research Group Prof 11 EE2011: Engineering Electromagnetics Electromagnetics Conductors • Example 5 Prof Joshua Le-Wei Li, EM Research Group Prof 12 EE2011: Engineering Electromagnetics Electromagnetics Dielectrics • Dielectrics: Concepts – Induced field is called a is polarization field polarization – Polar and nonpolar materials – Polarization property D = 0E+P – P= 0 eE: • Linear if P |E|; • Isotropic if P//E; • Anisotropic if E and D are in different directions; •...
View Full Document

This document was uploaded on 02/18/2014 for the course EE 2011 at National University of Singapore.

Ask a homework question - tutors are online