EE 307 Chapter 5 - Electric Fields in Materials

EE 307 Chapter 5 - Electric Fields in Materials - ECE 307:...

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Unformatted text preview: ECE 307: Electricity and Magnetism Spring 2010 Instructor: J.D. Williams, Assistant Professor Electrical and Computer Engineering University of Alabama in Huntsville 406 Optics Building, Huntsville, Al 35899 Phone: (256) 824-2898, email: williams@eng.uah.edu Course material posted on UAH Angel course management website Textbook: M.N.O. Sadiku, Elements of Electromagnetics 4 th ed . Oxford University Press, 2007. Optional Reading: H.M. Shey, Div Grad Curl and all that: an informal text on vector calculus, 4 th ed . Norton Press, 2005. All figures taken from primary textbook unless otherwise cited. 8/11/2010 2 Chapter 5: Electric Fields in Material Space Topics Covered Properties of Materials Convection and Conduction Currents Conductors Polarization in Dielectrics Dielectric Constant and Strength Linear, Isotropic, and Homogeneous Dielectrics Continuity Equation and Relaxation Time Boundary Conditions Homework: 9, 12, 17, 19, 22, 23, 24, 28, 32, 33, 34, 35, 37 All figures taken from primary textbook unless otherwise cited. 8/11/2010 3 Convection and Conduction Currents Current (in amperes) through a given area is the electric charge passing through the area per unit time Current Density is the amount of current flowing through a surface (amperes/m 2 ), or the current through a unit normal area at that point Depending on how the current is produced, there are different times of current density Convection current density Conduction current density Displacement current density (Chapter 9) Current generated by a magnetic field dt dQ I = S I J = = s S d J I 8/11/2010 4 Convection Current Density Convection current density Does not involve conductors and does not obey Ohms law Occurs when current flows through an insulating medium such as liquid, gas, or vacuum y v v Su t y S t Q I = = = u J u S I J v y v y = = = 8/11/2010 5 Conduction Current Density Conduction current density Current in a conductor Obeys Ohms law Consider a large number of free electrons traveling in a metal with mass (m), velocity (u), and scattering time (time between electron collisions), . The carrier density is determined by the number of electrons, n, with charge, e Conduction current density can then be calculate as Where is the conductivity of the conductor This relationship between current concentration and electric field is known as Ohms Law E E m ne u J ne u m E q F v v = = = = = = 2 8/11/2010 6 Conductors Conductors are materials with an abundance of free moving charges Convention states that when an electric field is applied to a conductor, the positive free charges are pushed along the same direction of the applied field, while the negative charges move in the opposite direction The free charges do two things...
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This note was uploaded on 12/14/2011 for the course EE 307 taught by Professor Williams during the Spring '10 term at University of Alabama - Huntsville.

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EE 307 Chapter 5 - Electric Fields in Materials - ECE 307:...

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