1

D.  CAPACITANCE

The principal characteristic of a capacitor is that it can store an electric charge (Q), which is directly
proportional to the capacitance value (C) and the voltage applied (V).

Q = CV

The charging current I is therefore defined as

I = dQ/dt = CdV/dt.

The value of capacitance is defined as one Farad when the voltage across the capacitor is one volt,
and a charging current of one ampere flows for one second.

C = Q/V =  Coulomb/Volt = Farad

Because the Farad is a very large unit of measurement, and is not encountered in practical applica-
tions, fractions of the Farad are commonly used, namely:

picofarad (pF)

= 10

-12

 Farad

nanofarad (nF)

= 10

-9

  Farad

microfarad (µF)

= 10

-6

  Farad

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