Demonstrations

Coulomb's Law Balance - Pasco Model

Code Number :	5A20.37
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 :	Electrostatics, Coulomb's Law
Area of Study :	Electricity & Magnetism
Equipment :	6 KV power supply, Coulomb's Law balance (Pasco Model), charging paddles, high voltage charging probe.
Procedure :	Zero the torsion pendulum before putting charge on the balls. Set the power supply at 5000 volts and touch one or both of the balls. Electrostatic repulsion or attraction can be shown and measured with this device. An interesting variation is to use only the torsion balance part of the apparatus and a metal plate. When the ball is charged, a "mirror charge" will be induced on the plate. The ball on the torsion balance will swing over, touch the plate, then be repelled. A discrepant event of the above demo is to use the black painted plate instead of the bare metal plate. In this case the ball will stick to the metal plate.

Websites

"A nice JAVA applet drawing E fields about charge distributions"
http://www.gel.ulaval.ca/~mbusque/elec

References

Peretz D. Partensky and Michael B. Partensky, "Hanging by a Thread", TPT, Vol. 44, # 2, Feb. 2006, p. 88.

Michael Partensky and Peretz D. Partensky, "Can a Spring Beat the Charges?", TPT, Vol. 42, # 8, Nov. 2004, p. 472.

Peter Anderson, "A Wind Shield for the PASCO Coulomb Apparatus," TPT, Vol. 41, # 1, p. 51, (Jan. 2003).

C. H. Worner, "On the Teaching of the Electric Dipole", TPT, Vol. 39, # 8, Nov. 2001, p. 462.

Robert Weinstock, "Two-Charge Dipole Revisited", TPT, Vol. 39, # 4, Apr. 2001, p. 218.

Christopher Bracikowski, "Graphical Analysis of Electric Fields of Dipoles and Bipoles," TPT, Vol. 38, # 1, p. 20, (Jan. 2000).

Leon M. Lederman, "Correction," TPT, Vol. 38, # 9, p. 519, (Dec. 2000).

Robert Weinstock, "Electric Field of a Two-Charge Dipole: A Graphical Approach Extended," TPT, Vol. 38, # 7, p. 430, (Oct. 2000).

Scott W. Bonham, John S. Risley, and Wolfgang Christian, "Using Physlets to Teach Electrostatics," TPT, Vol. 37, # 5, p. 276, (May 1999).

Adolf Cortel, "Demonstrations of Coulomb's Law with an Electronic Balance," TPT, Vol. 37, # 7, p. 447, (Oct. 1999).

Robert J. Beichner, "Visualizing Potential Surfaces With A Spreadsheet", TPT, Vol. 35 # 1, Feb. 1997, p. 95.

Sonya Cooper, Narasimha Prasad and Budh Ram, "Defining a Coulomb of Charge", TPT, Vol. 33, # 4, Apr. 1995, p. 198.

MArcelo Alonso, "More on the Coulomb", TPT, Vol. 33, # 6, Sept. 1995, p. 326.

Josip Slisko, Arkady Krokin, "Physics or Fantasy?", TPT, Vol. 33, # 4, Apr. 1995, p. 210.

David T. Kagan, "The Ultimate "Pith Balls", TPT, Vol. 29, # 4, Apr. 1991, p. 197.

Samaroo Deonarine, "Coulomb's Law After the Christmas Party", TPT, Vol. 28, # 9, Dec. 1990, p. 607.

Donald Mahoney, Clifford Swartz, "What is the Potential at a Point Due to a Line Source?", TPT, Vol. 22, # 6, Sept. 1984, p. 392 - 393.

Russell Patera, "Stability of the Coulomb Balance", TPT, Vol. 16, # 8, Nov. 1978, p. 565.

Wijit Senghaphan, Richard K. Fry, "Current Balance & Coulomb's Law apparatus", TPT, Vol. 12, # 7, Oct. 1974, p. 435.

D. F. Bartlett and E. A. Phillips, "An Experimental Test of Coulomb's Law", TPT, Vol. 8, # 7, Oct. 1970, p. 403.

Francis W. Sears, " A Substitute for Pith Balls and Balloons in the Demonstration of Electrical Forces", TPT, Vol.1, # 5, Nov. 1963, p. 225.

Bernard Roulet, Michel Saint Jean, "Image Charges Revisited: Beyond Classical Electrostatics", AJP, Vol. 68, # 4, p. 319, April 2000.

Ronald Shaw, "Symmetry, Uniqueness, and the Coulomb Law Force", AJP, 33, (4), April 1965, p. 300.

P. H. Wiley and W. L. Stutzman, "A Simple Experiment to Demonstrate Coulomb's Law", AJP, Vol. 46, (11), Nov. 1978, p. 1131.

Lawrie Challis and Fred Sheard, "The Green of Green Function," Physics Today, December 2003, p. 42.

Mail Questions and Comments to: Dale Stille