Demonstrations

R-C Time Constants

Code Number :	5F30.20
Disclaimer:	Reprinted by permission of Dick Berg, University of Maryland, for use on this website. The demonstrations contained and referenced herein are listed for the purposes of cataloging and describing physics demonstrations which should be conducted only under the direction of a trained instructional support professional or physicist. These demonstrations are not presented for the purpose of being conducted by persons unconnected to this Facility and/or persons not consulting with or being supervised by the recognized instructional support professional or physicist and his/her staff. The University is responsible only for those demonstrations carried out using its own equipment using established safety and scheduling policies, and bears no responsibility for those choosing to use this source material for their own purposes. All demonstrations described and contained herein are public domain, and can also be found in reference materials in libraries, bookstores, and electronic sources. Further information regarding legal liability in use of demonstrations and labs will be found on the web site Injuries in School/College Laboratories in USA. The University of Iowa Disclaimers: University of Iowa Disclaimer All Rights Reserved..
Condition :	Good
Principle :	Circuit Characteristics
Area of Study :	Electricity and Magnetism
Equipment :	2200 Uf Capacitor, 100 Ohm Resistor, 6 Volt Battery, Key Switch, Digital Oscilloscope, Resistor Box, Decade Capacitor Unit, Wave Generator (Wavetek).
Procedure :	Put the generator, resistor, and capacitor, in series as shown. Set the generator to the square wave function at around 100 Hz. Measure across the capacitor with the oscilloscope. Set the capacitor and resistor to the proper values to obtained the desired trace. Arrange the circuit as shown. The battery will charge the capacitor when the switch is pressed down. Release the key and the capacitor will discharge through the 1/2 watt, 100 ohm resistor. It is critical to set the scope as shown. The scope setting is stored at #10 in the Recall/Save menu. The standard oscilloscope will not allow you to observe voltage and current at the same time due to grounding parameters. To get around this drive two identical circuits from the same wave generator with one circuit having the components in reverse order of the other. In this way, the oscilloscope grounding remains valid for both cases and both can be shown on the same scope.

References

Biswajit Ray, "When Is a Capacitor NOT a Capacitor?", TPT, Vol. 44, # 2, Feb. 2006, p. 106.

Francis X. Hart, "Computer-Based Experiments to Measure RC", TPT, Vol. 38, # 3, Mar. 2000, p. 176.

Jim Oliver, "Observing Voltage Phases in RC, RL, and RLC Circuits." TPT Vol. 35, # 1, Jan. 1997, p. 30

Matthew J. Moelter and Rand S/. Worland, "A Child's Flashlight and RC Circuit Concepts", TPT, Vol. 35, # 1, Feb. 1997, p. 92.

John G. King and A.P. French, "Using a Multimeter to Study an RC Circuit," TPT, Vol. 33, # 3, p. 188-189, (March 1995).

Thomas A. Walkiewicz and James R. Kirk, "Characteristic Curves", TPT, Vol. 32, # 2, Feb. 1994, p. 90.

Herbert T. Wood, "The RC Circuit - A Multipurpose Laboratory Experiment", TPT, Vol. 31, # 6, Sept. 1993, p. 372.

Takao Tekeuchi, "It All Adds Up", TPT, Vol. 31, # 9, Dec. 1993, p. 518.

J. E. Gordon, and P. R. Grant, "Series RC Circuits Revisited", AJP, Vol. 72, # 5, May 2004, p. 655.

Norris W. Preyer, "Transient Behavior of Simple RC Circuits", AJP, Vol. 70, # 12, Dec. 2002, p. 1187.

David E. Wilson, "A Direct Laboratory Approach to the Study of Capacitors," AJP, 57, (7), July 1989.

John B. Kwasnoski, "Measuring the Charge Stored on a Capacitor," AJP, 57, (7), July 1989.

En-8, 10, 11, Eo-12: Freier and Anderson, A Demonstration Handbook for Physics.

E-405: "Chg. and Dischg. - Square Wave," DICK and RAE Physics Demo Notebook.

Ronald Newburgh, "Two Theorems on Dissipative Energy Losses in Capacitor Systems", Physics Education, Vol. 40 (4), July 2005, p. 370.

Robert Ehrlich, "Discharging a Capacitor Through a Voltmeter," Turning the World Inside Out, p. 151-152.

Mail Questions and Comments to: Dale Stille