Capacitors 2

Charging a Capacitor

As a capacitor is charged by a battery, it becomes progressively more difficult for electrons from the battery to reach the negative plate of the capacitor due to the repulsion by the electrons that got there first.
Hence the current in the circuit progressively decreases.

As a result of this, the voltage across the capacitors although increasing, increases at a decreasing rate.
Charging of the capacitor will stop when the voltage of the capacitor equals to the voltage of the battery that is charging it.

Discharging a Capacitor

When a capacitor is discharged (connected in a circuit to do something, like power a camera flash), the current flows out rapidly at first.

A similar pattern is observed for the voltage across the plates. There is a rapid drop in voltage.

IMPORTANT
• The CHARGING and DISCHARGING CURRENT graphs have the SAME shape.
• The VOLTAGE DISCHARGING has the same shape as the CURRENT graphs.
• It is only the VOLTAGE CHARGING graph that looks different.

Other Graphs

This equation is the capacitor equation.

Notice that C is proportional to A. (all other factors constant)

Also C is inversely proportional to d (all other factors constant)

If the axis is inverted, then the shape is as follows: