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The Unit of Capacitance

<^< Examples: Electric Field Strength | Course Index | Charge Capacitance and Voltage >^>

The unit of capacitance is the farad (F). A capacitor is said to have a capacitance of 1F if a current of 1A flows in it when a voltage changing at the rate of 1V/s is applied to it.

The current flowing in a capacitor will thus be proportional to the product of the capacitance (C) and the rate of change of applied voltage. Hence:

I = C x (rate of change of voltage)

This means that if a quickly changing voltage is applied to a capacitor a relatively large current will flow in it. Conversely, if a slowly changing voltage is applied to a capacitor then a relatively small current will flow in it. In the extreme case, when a constant voltage is applied to a capacitor (for example when the voltage is applied from a D.C. source or a battery) no current will flow at all except for the initial charging of the capacitor which occurs when the supply is first connected.

Voltage increasing at 0.01 Vs-1 Voltage increasing at 0.1 Vs-1 Voltage increasing at 1 Vs-1 Voltage increasing at 10 Vs-1

0.01 A/s 0.1 A/s 1 A/s 10 A/s

<^< Examples: Electric Field Strength | Course index | Charge Capacitance and Voltage >^>