The purpose of this experiment is to determine the position of the equipotential contours between two conductors to which a potential difference has been applied. The apparatus is sketched below. As the sketch indicates the potentials are measured on a planar surface and the equipotentials are lines on this surface.
The potential difference between the electrodes is supplied by a d.c. (constant voltage) power supply. The value of the potential between the conductors (relative to the negative conductor) is measured with a voltmeter.