A conductive sphere is mounted on the end of an insulating, counterbalanced rod and suspended from a very thin torsion wire. An identical sphere is mounted on a calibrated linear track and can be positioned at various distances from the first sphere. When the conductive spheres are charged, the force between them is proportional to the twist of the torsion wire that is required to bring the balance back to its equilibrium position. Introductory physics students can determine the Inverse Square Law in a simple experiment, while advanced students can perform investigations into all the variables involved in electrostatic repulsion.
PASCO's Coulomb's Law Experiment features a calibrated track designed to minimize mirror charges, which can significantly affect experimental results. In addition, the conducting sphere connected to the torsion wire is magnetically damped. This allows force measurements to be made quickly, reducing the traditional difficulties with leakage currents.
This experiment is available for Download at no additional cost.
Note: This experiment can be performed as a standalone activity. However, it can also incorporate data collection software for further analysis. The supplied files are for DataStudio software but they can also be opened using PASCO Capstone software. See the videos section for details.