capacitors

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  • Created by: Anwen
  • Created on: 22-05-14 21:08
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  • 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

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