Capacitance Revised: 2012Aug06

3. Capacitance 2 Leyden Jars Volta’s law of capacitance Energy storage

a. Leyden Jar 3 Invented in 1745 by Pieter van Musschenbroek (1700–1748) as a device to store “electric fluid” in a bottle

b. Alessandro Volta’s law of Capacitance 4 1776 Law of Capacitance: Stored charge is proportional to applied voltage: Q=VC Capacitance “C” is measure of ability to store charge. Units: Farad=Coul/Volt Common unit is “microfarad”

bii. Parallel Plate Capacitor 5 Capacitance is a function of geometry of plates:

biii. Capacitors in circuits 6 Capacitors in Parallel is like 2 tanks next to each other (same voltage). Total capacitance: C = C1+C2 Capacitors in series (have same charge), total capacitance is:

c. Capacitive Energy Recall spring: F=kx, energy stored: 7 Recall spring: F=kx, energy stored: For capacitor: Q=CV, energy stored Energy is stored in the electric field between the plates

References 8 Misc http://www.circuitstoday.com/working-of-a-capacitor static electricity animations at http://www.physicsclassroom.com/ History at: http://www.hkcapacitor.com/capacitor/Capacitor-History.html http://www.sparkmuseum.com/LEYDEN.HTM http://maxwell.byu.edu/~spencerr/phys442/node4.html http://en.wikipedia.org/wiki/Timeline_of_Fundamental_Physics_Discoveries