Part 4: Plotting Equipotential Lines

The locus of points which have the same value for potential forms an equipotential surface (or in this 2-dimensional experiment, an equipotential line).

 Restore the plate connections to what you had in Part 1. Again, remember to first turn off the power supply on PASCO before switching the wires. Begin by moving the probe slowly around on the resistance paper to get a feeling for the shape of an equipotential line; you should be moving the probe in such a way that the voltmeter reading stays constant (you stay on an equipotential line).

Now trace out the 5 volt equipotential. Start from the y-axis (x = 0) – see Figure 2 – and enter the data in Table 4 in the lab report. Plot only as many points as needed to define the curve along the resistance paper, going from the region inside the parallel plates to outside the plate as far as you can still trace out the equipotential line. It is probably more efficient to start with a coarse grid and then come back to fill in extra points wherever sharp bends in the curve demand extra detail. Plot a smooth curve connecting the points in a manner consistent with the uncertainties determined earlier.

Repeat for the 4 and 3 volt equipotential lines. Assuming that the 3 volt (half of the power supply voltage) equipotential is a line of mirror symmetry, you can now draw in, without further measurement, the 2 and 1 volt equipotentials. If in doubt, you can measure them in part or in full.