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An Apparatus to Demonstrate the Energy Stored in a Capacitor. AAPT Summer Meeting Syracuse New York July 24, 2006. Andrew Tomasch. Experimental Goals. To demonstrate that capacitors store energy that can be retrieved as mechanical work
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An Apparatus toDemonstrate the EnergyStored in a Capacitor AAPT Summer Meeting Syracuse New York July 24, 2006 Andrew Tomasch University of Michigan Andrew Tomasch
Experimental Goals • To demonstrate that capacitors store energy that can be retrieved as mechanical work • To deduce from the experimental data that the energy stored in a capacitor is proportional to the square of the potential to which it has been charged Andrew Tomasch University of Michigan
Overview Servo 2 Meter Long Aluminum Rule 300 g Mass 1 Farad Capacitor Power Supply Andrew Tomasch University of Michigan
Experiment Design • Servo mounted directly to measuring scale attached to support rail • Slotted support rail clamped to table via corner brackets • Power supply, DVM and Capacitor on table • Banana jacks for all connections Andrew Tomasch University of Michigan
Experiment Construction • Based on inexpensive, high-quality hobby industry motor/gearbox • Design requires a minimum of skilled fabrication—most parts are adapted with little or no modification • Parts readily available from commercial sources • Screwdriver assembly suitable for student labor • Minimal machine shop time required to reduce cost Futaba S3003 Radio Control Servo Andrew Tomasch University of Michigan
Theory of Operation Work Done Against Gravity = Efficiency x Stored Energy Andrew Tomasch University of Michigan
Data (Linear Plot) Andrew Tomasch University of Michigan
Data (Log Plot) Typical Efficiency for Motor/gearbox is ~25% Andrew Tomasch University of Michigan
Data (Student Worksheet Plot) 6 Volts 3 Volts 2 Volts Lower Efficiency at Low Voltages Steepens Exponent Slightly Andrew Tomasch University of Michigan
Summary and Conclusions • The apparatus is easy to construct from commercial parts with minimal fabrication • The experiment is robust and has been successfully tested in the undergraduate labs during the 2006 winter semester • The data tend to yield exponents slightly steeper than 2 due to lower motor efficiency at low potentials. The effects are small enough to neglect Andrew Tomasch University of Michigan