Before starting this module, you should be able to: When you complete this module, you should be able to: 
  • Cite some common dielectric materials.
  • Describe how an electrical charge is stored in a dielectric material.
  • Define a coulomb of electrical charge.
  • Define capacitance in terms of two conductors and a dielectric.
  • Describe the meaning of charging capacitor and discharging a capacitor.
  • Explain how AC current flows in a capacitor circuit, but with none flowing through the capacitor, itself.

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 Capacitor Charge and Discharge 
in a DC circuit 
 

Charge Effects

  • The source of current in this circuit is the DC voltage supply, Vs.
  • Current flows through this circuit in a counter-clockwise direction.
  • The current charges the plates of the capacitor, but does not flow through the capacitor, itself. 
  • Current flows in this circuit until the capacitor is completely charged--until the voltage across the plates of the capacitor is equal to the voltage source, Vs.

Discharge Effects

  

  • The source of current in this circuit is the energy that has been stored in the capacitor.
  • Current flows through this circuit in a clockwise direction.
  • The current discharges the plates of the capacitor, but does not flow through the capacitor, itself.
  • Current flows in this circuit until the capacitor is completely discharged--until the voltage across the plates of the capacitor is zero.

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lbldef.gif (1302 bytes)
Capacitor Charge and Discharge 
in an AC circuit

 

While the applied voltage is increasing during the positive half-cycle, current flows through the circuit clockwise to charge the plates of the capacitor.
While the applied voltage is decreasing during the positive half-cycle, current flows thorugh the circuit counter-clockwise to discharge the plates of the capacitor
While the applied voltage is increasing during the negative half-cycle, current flows through the circuit counter-clockwise to charge the plates of the capacitor with the opposite polarity.
While the applied voltage is decreasing during the negative half-cycle, current flows thorugh the circuit clockwise to discharge the plates of the capacitor

 

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