Therefore, we will determine the equipotential surfaces in the presence of a small DC current and use them to draw conclusions about the equipotentials and electric field lines of the electrostatic problem. The small current is obtained by connecting a power supply to the silver electrodes painted on special conducting paper. The conducting paper also contains a grid, or coordinate system, to facilitate location of points. When the galvanometer indicates no current between two points, it indicates that there is no potential difference between the two points, i.e. they are on the same equipotential. Here the galvanometer is being used as a null indicator .
Measurements involving null indicators tend to be precise because they involve no reading of dials.
Hook up the circuit shown in Figure 2. Have your instructor check the wiring. Mount the high resistance conducting paper with the parallel plate configuration onto the board, making sure that the spring-mounted contacts are firmly set on the silver electrodes. Use sandpaper, only if necessary, to rub the contacts for a better connection. Turn on the power supply.