MODIFIED KELVIN TECHNIQUE FOR MEASURING STRAIN-INDUCED CONTACT POTENTIALS

We discuss the principles required to determine the electric field outside a metallic conductor created by strain gradients in the metal as might be engendered by the Earth's gravity. The experiment we describe measured the contact potential variation between a mechanically differentially strained metal surface and an unstrained capacitive sensing probe. The results are of considerable importance for the investigation of the free fall of charged particles inside vertical conducting drift tubes. Our aim here is to elucidate the large sources of error associated with the application of strain. These include motions of the sample and temperature variations. The solutions we have developed may find application in similar experiments.