Setup: A capacitor and a light bulb/resistor are connected in series with a battery. The circuit is closed so that the capacitor can be charged. The brightness of the light bulb is an indication of magnitude of the current flow. After the Capacitor is charged, the capacitor is then connected across the light bulb to show that it is charged.

Observations:  

• When the circuit is first closed the flow of current is the same as it would be if there were no capacitor in the circuit.
• As the capacitor gains charge the current flows drops off exponentially. See charging a RC circuit. The dimming of the light bulb is visual demonstration of the exponential drop in the current.
• The magnitude of the capacitor (100,000 mF) was chosen to be large so that the time constant of the RC circuit would be large. In this case, t = R C ~ 5 sec. The resistance of a light bulb changes with the current flowing through it (it is a non-Ohm) so the time constant is not a fixed number like it would be for a fixed resistance.
• After the capacitor is charged and then connect across the resistor, the initial current is the same as when the battery was first connected. The current then decays away with the "same" constant as it did when the capacitor was charging.