Measurement of electrical forces using a modified torsion balance and capacitance transducer

The attractive force between two conducting electrodes, one charged and the other at nominally zero potential, has been measured using a modified torsion balance whose deflection is monitored by a linear rotary differential capacitance (LRDC) transducer. This device has a resolution of 10−7 rad and is simple to operate. The results for different electrode geometries as a function of separation distance and voltage on the charged conductor agree to ±20% or better with theoretical results, in most cases. In the case of aluminum electrodes, the attractive force is not stable; rather, it varies periodically as the result of an unknown discharge process.