Physics - Discharging capacitors
Voltage and current versus time graphs also display exponential
relationships during discharge. Recall that the capacitor would initially
be fully charged, that is at a voltage that corresponds to the supply, and
no current is flowing. The capacitor will maintain this voltage as long as
the battery is connected. To discharge a capacitor, the battery must be
disconnected and the leads of the capacitor shortened as shown.
The electrons flow from plate X through the wire to plate Y. At first a
very large current will flow because there is maximum voltage across the
capacitor and little resistance to the flow of electrons. The voltage
across the capacitor therefore drops rapidly at first. As the voltage
across the capacitor reduces, the amount of current flowing in the circuit
also reduces. This continues until there is no longer an excess of
electrons on plate X to supply the electron flow. Note that the voltage
across the capacitor drops by two thirds during one time constant, as does
the size of the current.
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