lecture6 - Lecture 6 Capacitance In this lecture you will...

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1 ECE 303 – Fall 2005 – Farhan Rana – Cornell University Lecture 6 Capacitance In this lecture you will learn: • Capacitance • Capacitance of Some Simple Structures • Some Simple Solutions of Laplace’s Equation ECE 303 – Fall 2005 – Farhan Rana – Cornell University Capacitance Consider two metallic objects connected by a voltage source V + - + + + + + + + + + + + + + + - - - - - - - - - - - - - - • The total charge on both metal objects have the same magnitude but opposite sign • The charge is proportional to the applied voltage: V Q total charge + Q total charge - Q • The constant of proportionality is called the capacitance C : CV Q = • Capacitance has units Coulombs/Volts or Farads • More generally, capacitance is also defined as: dV dQ C =
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2 ECE 303 – Fall 2005 – Farhan Rana – Cornell University Capacitance of Parallel Plates V +- φ = V = 0 area = A d V E x = d V o L ε σ = d V o R = + + + + + + + + - - - - - - - - d A V Q dV dQ C V d A Q o o = = = = d From previous lectures: ECE 303 – Fall 2005 – Farhan Rana – Cornell University Capacitance of Concentric Cylinders + + + + + + + + - - - - - - - - V () = a b r V r E r ln a b b V o out ln = a b a V o in ln = a b V Q dV dQ C a b b V b Q o o ln 2 length unit per e capacitanc ln 2 length unit per charge π = = = = = = Since the structure is infinite in the z-direction (i.e. in the direction coming out of the slide) one can only talk about capacitance per unit length (units: Farads/m) b a From previous lectures:
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This note was uploaded on 02/02/2008 for the course ECE 3030 taught by Professor Rana during the Fall '06 term at Cornell.

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lecture6 - Lecture 6 Capacitance In this lecture you will...

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