5H40.40 - Current Balance

Code Number:
5H40.40
Demo Title:
Current Balance
Condition:
Excellent
Principle:
Magnetic Fields Around Current Carrying Wires
Area of Study:
Electricity & Magnetism
Equipment:
Variac, 6 Volt - 15 Amp Transformer, Amp Meter, Current Balance Apparatus, Laser.
Procedure:

Arrange the apparatus as shown. Adjust the balance so that it moves freely and the top wire is just balanced above but not resting on the bottom wire. Adjust the pitch of the mirror so that the laser reflection will show clearly on the classroom screen. Turn up the Variac but watch the amp meter and do not exceed 15 amps. The parallel wires will repel each other farther as more current is applied. The laser reflection may be observed and/or measured.

References:
  • Benjamin Oostra, "The Wire Balance", TPT, Vol. 54, #9, Dec. 2016, p. 560.
  • Yaakov Kraftmakher, "Classroom Demonstration of Magnetic Force", TPT, Vol. 42, #8, Nov. 2004, p. 500.
  • K. A. Fletcher, S. V. Iyer, and K. F. Kinsey, "Some Pivotal Thoughts on the Current Balance", TPT, Vol. 41, # 5, May 2003, p. 280
  • W. Herreman and R. Huysentruyt, "Measuring the Magnetic Force on a Current-Carrying Conductor", TPT, Vol.  33, # 5, p. 288 - 289 May 1995.
  • John Wessner, "The Average Bears Noting", TPT, Vol. 31, # 9, Dec. 1993, p. 548.
  • Thomas B. Greenslade, Jr., "Modified Current Balance", TPT, Vol. 22, # 8, Nov. 1984, p. 540.
  • Wijit Senghaphan, Richard K. Fry, "Current Balance & Coulomb's Law Apparatus", TPT, Vol. 12, # 7, Oct. 1974, p. 435.
  • J. Harris and A. Ahlgren, "Some Simple Experiments and Demonstrations", TPT, Vol. 4, # 7, Oct. 1966, p. 314.
  • D.S. Ainslie, "Electric Current Balance for Lecture Demonstrations and Laboratory Experiments",  TPT, Vol. 2, # 3, March 1964, p. 128.
  • Jose Arnaldo Redinz, "Forces and Work on a Wire in a Magnetic Field", AJP, Vol. 79, # 7, July 2011, p. 774.
  • Harriet Slogoff and Robert Smith, "A Reliable and Accurate Current Balance for the Elementary Physics Laboratory", AJP, Vol. 53, #12, Dec. 1985, p. 1213.
  • R. Nielsen Hopkins and George Loomis, "Modified Current Balance for the Elementary Physics Laboratory", AJP, Vol. 45, # 6, June 1977, p. 590.
  • Ei - 5:  Freier and Anderson,  A Demonstration Handbook for Physics.
  • W. Bolton, "A Current-Carrying Conductor In A Magnetic Field", Book 4 - Electricity, Physics Experiments and Projects, 1968, p. 41-42.
  • W. Bolton, "The Force Between Current-Carrying Conductors", Book 4 - Electricity, Physics Experiments and Projects, 1968, p. 43-44.

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.