# 5F20.30 - Potentiometer

Code Number:
5F20.30
Demo Title:
Potentiometer
Condition:
Excellent
Principle:
Resistance and Voltage Changes
Area of Study:
Electricity & Magnetism
Equipment:
Two 'D' Cell Batteries, Uniform Slide Wire, Galvanometer, Special Resistor for Galvanometer.
Procedure:

Arrange as illustrated. Insert the special resistor into the binding posts on the galvanometer. You will now have full scale deflection when using 'D' cell batteries. Push the key switch until it touches the slide wire and observe the deflection. Reposition until zero deflection is observed. If used with a standard cell the value of the other cell may be calculated.

The special resistor is always kept with the potentiometer slide wire board.

Jasper Halekas uses a simplified version of this to show varying voltage with resistance.  Use one of the meter sticks with the 13 ohm/meter wire attached to it and the LED and battery arrangement from the 5D10.25, "Conducting Foam" demo box.

An interesting variation is to place another cell into one leg of the potentiometer loop.  Shown is a wet cell consisting of a copper and zinc electrode using a dilute solution of acetic acid as the electrolite.  The equilibrium point moves down to approximately the 27 cm position.

References:
• James N. Boyd, "Parallel Circuits and Probability", TPT, Vol. 26, # 2, Feb., 1988, p. 106.
• Fred B. Otto, "The Slide-Wire Potentiometer - A New Approach", TPT, Vol. 23, # 4, Apr. 1985, p. 232.
• Robert W. Bird, "A Low Reference Voltage", TPT, Vol. 22, # 8, Nov. 1984, p. 539.
• Thomas B. Greenslade, Jr., "Reversible Meter Bridge", AJP, Vol. 73, # 5, May 2005, p. 398.
• William C. Smith, "Inexpensive Student Potentiometer", AJP, 33, # 8, Aug. 1965, p. 603.
• Eg - 7:  Freier and Anderson,  A Demonstration Handbook for Physics.
• E-161:  Richard Manliffe Sutton, Demonstration Experiments in Physics.
• Borislaw Bilash II, David Maiullo, "The Shorter. the Brighter", A Demo a Day: A Year of Physics Demonstrations, p. 275.
• Simon Quellem Field, "More About Magnets", Gonzo Gizmos, p. 11-14.
• "Potentiometer",  The New Illustrated Science and Invention Encyclopedia,  p. 2031
• Walter C. Michels,  Electrical Measurements and Their Applications, p. 56-64.
• "Ohm's Law in Simple Circuits", Selective Experiments in Physics, CENCO, 1962.
• "Ohm's Law", Selective Experiments in Physics, CENCO, 1962.
• "The CENCO Potentiometer: Calibration of Ammeter and Voltmeter", Selective Experiments in Physics, CENCO, 1962.
• W. Bolton, "The Potentiometer", Book 4 - Electricity, Physics Experiments and Projects, 1968, p. 5-6.
• Borislaw Bilash II, “Resisting the Flow“, A Demo A Day – A Year of Physical Science Demonstrations, p. 282.

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.