Unformatted text preview: s on the right plate of C2, an equivalent amount of negative charge is removed from the left plate of C2, leaving it with an excess positive charge • All of the right plates gain charges of –Q and all the left plates have charges of +Q Equivalent Capacitance, Example • The 1.0μF and 3.0μF are in parallel as are the 6.0μF and 2.0μF • These parallel combinations are in series with the capacitors next to them • The series combinations are in parallel and the final equivalent capacitance can be found Energy Stored in a Capacitor
• Assume the capacitor is being charged and, at some point, has a charge q on it • The work needed to transfer a charge from one plate to the other is • The total work required is Energy, cont
• The work done in charging the capacitor appears as electric potential energy U • This applies to a capacitor of any geometry • The energy stored increases as the charge increases and as the potential difference increases • In practice, there is a maximum voltage before discharge occurs between the plates Energy, final
• The energy can be considered to be stored in the electric field • For a parallel plate capacitor, the energy can be expressed in terms of the field as • U= ( oAd)E2 • It can also be expressed in terms of the energy density (energy per unit volume) E2 uE = o Capacitors with Dielectrics
• A dielectric is an insulating material that, when placed between the plates of a capacitor, increases the capacitance
– Dielectrics include rubber, plastic, or waxed paper • With a dielectric, C = Co
– The capacitance is multiplied by the factor when the dielectric completely fills the region between the plates – For a parallel plate capacitor, this becomes – C = o(A/d) Dielectrics – An Atomic View
• The molecules that make up the dielectric are modeled as dipoles • The molecules are randomly oriente...
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This note was uploaded on 02/03/2010 for the course NEUROSCI 101A taught by Professor Scheibell during the Winter '10 term at UCLA.
- Winter '10