# 19.2.1 Capacitor Discharge Graphs

### Capacitor Discharge Graphs

• So far, only capacitors charged by a battery have been considered
• This is when the electrons flow from the positive to negative plate
• At the start, when the capacitor is charging, the current is large and then gradually falls to zero
• Capacitors are discharged through a resistor
• The electrons now flow back from the negative plate to the positive plate until there are equal numbers on each plate
• At the start of discharge, the current is large (but in the opposite direction to when it was charging) and gradually falls to zero
• As a capacitor discharges, the current, p.d and charge all decrease exponentially
• The means the rate at which the current, p.d or charge decreases is proportional to the amount of current, p.d or charge it has left
• The graphs of the variation with time of current, p.d and charge are all identical and represent an exponential decay
• The key features of the discharge graphs are:
• The shape of the current, p.d. and charge against time graphs are identical
• Each graph shows exponential decay curves with decreasing gradient
• The initial value starts on the y axis and decreases exponentially
• The rate at which a capacitor discharges depends on the resistance of the circuit
• If the resistance is high, the current will decrease and charge will flow from the capacitor plates more slowly, meaning the capacitor will take longer to discharge
• If the resistance is low, the current will increase and charge will flow from the capacitor plates quickly, meaning the capacitor will discharge faster ### Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
Close Close