Concept

The enery stored in the capacitor is $E=\frac{1}{2}CV^2$, where C is the capacitance and V is the changing voltage (chosen to be 25% larger than the maximum voltage rating of the capacitor). This energy is dissipated through a light bulb where the time to discharge is RC. Here, the resistance of the system, R, is assumed to reside primarily in the light bulb. Because the bulb has a metal filament, its resistance is temperature dependent and not easily estimated based on the power rating of the bulb. However, as expected, the 15W bulb has a significantly larger resistance than the 150W bulb, and thus stays lit noticeably longer.

Procedure

Verify that the Bulb/Capacitor Board is plugged into the B+ Volts input of the power supply and that thevolt meter is switched towards the B+ Volts side as shown in the top-right picture
With the Bulb/Capacitor Board’s toggle switch is oriented towards the capacitor (connecting capacitor tobulb) turn on the power supply’s AC switch and then its DC switch. The power supply light should come onand now be supplying 100V.
When ready to demonstrate, toggle the Bulb/Capacitor Board’s switch away from the capacitor to begincharging it. The capacitor becomes more charged as the current meter drops to zero.
To light the bulb, toggle the Bulb/Capacitor Board’s switch back towards the capacitor to connect thecapacitor to the light bulb.
The 150W bulb will stay lit for about 2 seconds. The 15W light bulb will stay lit for about 10 seconds.

Equipment

Bulb/Capacitor Board with:
Large Light Bulb (150W, 120V)
Small Light Bulb (15W, 120V)
Capacitor (8400μF, 100V)
High Voltage Power Supply