# capacitors

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• Created by: Anwen
• Created on: 22-05-14 21:08
• Capacitance
• Capacitors in Series
• V1=Q/C1 V2=Q/C2 V=Q/C1+Q/C2 V=Q/C Qisconstant 1/C=1/C1+1/C2
• key words
• Capacitor
• is a pair of conducting plates separated by an insulator. If a PD is placed across the plates they aquire equal and opposite forces
• Capacitance of a capacitor
• change on either plates ___________ PD between the plates
• Dielectric
• Insulator between the plates of a capacitor also serving to make capacitance larger than if there were just an empty space (usually made of porcelain or paper)
• Capacitors in Parallel
• Q1=C1*V Q2=C2*V Q=C1V+C2V C=C1+C2
• charged and discharged capactitors
• Q=Qoe^-t/CR V=Voe^-t/CR T=CR (time.it.takes) T=Q/I
• Discharging= Q=Qoe^-t/CR
• Qo initial charge (when capacitor is full of energy)
• Charging = Q=Qo(1-e^-t/CR)
• Qo final charge (when capacitor is full of energy)
• Parallel plate capacitance
• Q.prop.V Q.prop.A Q.prop.1/d
• Combining giving Q.prop.VA/d
• The constant is determined by what's inbetween the two plates (the dielectric) If this is a vacuum or air then the constant is £o
• Q=£oVA/d C=Q/V C=£oA/d
• Energy stored in a capactior
• E=1/2QV =1/2Q^2/C =1/2CV^2