PART 1: Measuring the Electric Potential Between Parallel Plates

Connect the clamps from the power supply to the contacts of plates “A” and “B” on the resistance paper, making plate “A” the negative side. The spare plate (plate “C”) will be used later on. Connect the black (negative) clamp of the voltmeter to the negative plate; this point is assigned a potential of zero. Since only potential differences are important, we may always choose to assign a potential of zero to some point called the “ground”.

Open the PASCO Capstone software and click on “Signal Generator”. Change the waveform to “DC”, set it to 6 Volts, and turn on the power. Set the multimeter to measure DC volts on a suitable range (20 V in this lab). Place the handheld red (positive) lead of the voltmeter on the contact point of plate “B” and check to make sure you read 6.00 Volts. Check the voltage along each conducting line (plate) for consistency.

Consider a line perpendicular to the plates, through approximately the centre of each plate.  Use the positive (red) voltmeter probe to measure the potential at 10 equally spaced positions along this horizontal line (which we will refer to as the central line), using the negative plate as the reference point. Record your data in Table 1. Take note of the position of this central line (without writing on the black paper!), as it will be needed in part 2.

In order to determine how accurately you can measure the potential at any given point, you will make repetitive measurements at one point and use some simple statistics. To do so, pick one point along the central line and measure its voltage 10 times using the multimeter by repeatedly placing the probe on the same point and reading the voltage measurement every time. Record those numbers under Table 1 in the space provided for uncertainty measurements. Then use Microsoft Excel and the function =STDEV() to calculate the standard deviation between these points. Add this value to the uncertainty in the digital multimeter given in the previous section and record the resulting value as the uncertainty in your measurement.

Calculate the potential change between adjacent points and record in Table 1. You will use this later in the lab.

Repeat your measurements along a line parallel to and about 5 cm from the central line, i.e., closer to the open end of the plates. Compare the results for these two sets of measurements by plotting a graph of potential versus distance for each set of measurements, using Microsoft Excel. Plot both sets on one graph, using appropriate labelling. Then plot the line of best fit for each, displaying the slope of the lines and the values ( value is a measure of the goodness of fit: the closer it is to 1.0, the better the fit made to the data).

Note: To plot multiple data sets on one graph in Excel, once you made the first plot, click on the plot area, then go to “Chart Design” and click on “Select Data”. Give your first set of data a name, then click on “Add” or the “+” sign to add the second data set to your graph. Give it a different name, then click on the box in front of “X values” and select the data. Do the same thing for “Y values” and click “OK”.