Current Electricity: Capacitance

Capacitance  Scalar quantity Unit = farad Symbol = C

C = Q/V Q = charge V = voltage

Capacitor An electric device capable of storing electric charge In an electric circuit, electrons flow from the negative battery terminal to the right-hand plate of the capacitor, and then from the left-hand plate of the capacitor to the positive battery terminal

Parallel Plate CapacitorPair of metal plates separated by a dielectric (thin sheet of insulated material)Factors affecting capacitance: Common area shared by the plates Permittivity of medium between the plates Distance between the plates

Capacitance of a parallel plate capacitor: C = εA/d ε = permittivity A = common area d = distance

Energy stored in a capacitor: The work done by the battery to charge the capacitor W = 1/2 CV²

Capacitors conduct A.C. but not D.C.  When connected to an A.C. supply, electron flow changes direction as the polarity changes. In a D.C. circuit, the current flows in one direction. Once the capacitor is charge to the same voltage as the battery, no more current flows.

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