PURPOSE: To show the mechanical equivalent of the electric energy stored in a capacitor, and to show that this amount of energy is proportional to the square of the voltage.
DESCRIPTION: A .050 Farad 15 Volt capacitor is connected to a DC power supply. A double pole double throw knife switch is used to disconnect the power supply from the cap and discharge the cap to a small DC motor that has a pulley and string connected to a tennis ball. When the cap is charged to 7.5 Volts the motor will lift the tennis ball about .5 meter. When charged to 15 volts the tennis ball is lifted to a height of two meters.
EQUIPMENT: Small DC motor with pulley and tennis ball, 50,000 uF 15 VDC electrolytic capacitor, double pole double throw knife switch, DC power supply, holder, bench clamp, long rod and clamp.
SET UP NOTES:
DEMONSTRATION NOTES: The cap that works best is a 50,000 uF, 15 VDC electrolytic capacitor. The motor is a Radio Shack catalog number 273-255 High Speed 12VDC motor with 11,500 rpm. The mass is a tennis ball. The pulley and motor shaft coupling were custom made of brass by the Brown Machine Shop.
edited by JZ on 2/18/02