Current Electricity: Capacitance

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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 Capacitor

Pair 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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