Dr. Thomas E. Wilson, Professor of Physics, won first place in the Apparatus Competition held during the American Association of Physics Teachers National Meeting in Cincinnati July 22-26 for his entry titled “Kelvin Ampere Balance”. His entry won in the two separate apparatus categories of low-cost and unlimited cost. As per the AAPT description of the Competition (See https://www.aapt.org/Programs/contests/apparatus_home.cfm):
“The Apparatus Competition was established to recognize, reward, and publicize worthwhile contributions to physics teaching through demonstration and experiment.
With huge advances in technology, many physics apparatus are now commercially available. But even with these advances, physics research still requires the inventive spirit of designing and building experimental apparatus one’s self.
Whether developed to pique the interest of students, used in lecture and demonstration, or simply used to help teach physics in new or fascinating ways, teachers are continually engineering apparatus to aid physics instruction. The Apparatus Competition is where teachers can share their apparatus with others.
The Competition is held annually during AAPT’s summer meeting and is open to all members.”
Abstract: We have developed a compact and low-cost 3D-printed version of the Kelvin Ampere Balance. Almost every undergraduate physics major does an experiment with a current balance to investigate the magnetic force between parallel current-carrying wires. Present commercially available balances exceed $1000 in cost and require specialized power supplies capable of 10 amperes or more. Our device is low cost ($80 in parts and 3D-printing charges) and, by taking advantage of superposition of many circular turns of current carrying wire to amplify the magnetic force, quite a detectable force is created even for currents of less than 1 ampere. The low current needs of the associated power supply places it into the range of more inexpensive power supplies already found in many teaching laboratories. These features should allow it to be placed into the general physics introductory laboratory at both the university and secondary school level. Two current coils, each wound with a large number of turns of enameled-magnet wire, and are positioned parallel and coaxially to each other on a low-cost digital scale using 3-D printed stand. The measured magnetic force and theory agree within 3%. In addition, the mutual inductance can also be measured directly and it agrees with theory to within 2%.
Wilson’s Kelvin Ampere Balance will soon be commercially available from TEL-Atomic, Inc. TEL-Atomic has been providing tools to teach advanced physics since 1978. (See: https://www.telatomic.com)
Wilson acknowledged the assistance of Ronald Cabacar of RCBI for the 3-D printing.
Photo: Front view of apparatus showing AWS Gemini-20 digital scale, lower coil on a pedestal resting on the scale pan, and a supporting stand for a second coil.