Experiment 15
ELECTRIC FIELDS

AND

ELECTRIC POTENTIAL

PROCEDURE

Parallel plates

Open up the Electric Workbook and fill in the header information. The field mapping apparatus consists of special graphite impregnated paper with metallic electrodes painted on it to simulate the distribution of electric charge that makes up the field source.

Take the parallel plate electrode sheet and note that there is a set of 1 cm X 1 cm grid squares printed on it as indicated by the crosses at each corner. The full sheet has a total of 29 marks along each horizontal row (counting the boundaries at 0 and 28), and 21 marks along each vertical column (counting the boundaries at 0 and 20).

Mount the parallel plate electrode arrangement on the board provided. Connect the 30 V @ 1 A supply leads to make good contact with each electrode. Before switching the supply on make sure that the control knob is turned fully counter-clockwise. An illustration of the set up is shown below:

NOTE: If the electrical supply is provided through the distribution outlet on your bench, a knife switch has been supplied in the circuit. Please keep the switch open at all times when you are not making measurements.

Equipotential Measurements on the Parallel Plate Configuration
 

1. Connect the digital voltmeter across the two electrodes on the board.  Set the buttons to read volts on the 20 volt scale. Turn on the power supply and slowly increase the voltage knob until the voltmeter reads 5.0 volts.  Record the voltage in cell M11.  Disconnect the voltmeter.
2. Use an alligator clip to connect the black probe to the electrode that is connected to the negative power supply terminal.  The red probe will be used to record the data at every other grid point on the paper.  The data will consist of series of voltages taken along a specific column of grid points on the paper, that is each series will consist of 11 points, ranging from row 0 to row 20, by twos (e.g., 0, 2, 4, 6, ……, 20).  The next series will be measured along column #2, and so forth, until 15 series of 11 data points are taken. See the outline plan in Figure 15-3 below.

Fig. 15-3: Grid Numbering Arrangement