# Surfing an Electric Field

## PURPOSE

The purpose of this lab is construct an electric field map by measuring and recording the potentials at different positions. Microsoft Excel will be used to build a three-dimensional field map.

## MATERIALS

• Conductive Paper
• 1.5-volt Battery
• Digital Multimeter
• Wires
• Push Pins
• Cardboard

## SET UP THE APPARATUS

1. Make a sketch of the silver electrodes that are on your conductive paper . Make your sketch as representative as possible of the actual electrodes, including any numbered coordinates.

2. Connect the battery to the electrodes, with one wire leading to each. On your sketch, indicate which electrode(s) is connected to positive (+) and which is connected to negative (-). Connect the negative lead (COM) from the DMM (the black one) to the negative lead either at the battery or on the electrode.

3. Rotate the selector knob of the DMM until it reads 2 VDC (or 2000 mvdc). The maximum voltage that can be read at this setting is 1.999 volts. Touch the positive lead (the red one) to the negative electrode. It should read 0 volts. Touch it to the positive electrode, which should read approximately 1.5 volts.

4. Launch Microsoft Excel and open the file "EFields.xcl". One partner will need to handle the computer data entry.

## PROCEDURE

5. Beginning at one corner of the sheet, place the tip of the red probe at an intersection (such as 0,0). Read the voltage to the nearest 0.01 volt and record in the Excel data table.

6. Move across the pattern, recording the voltage at each intersection. Use the same pressure on the probe each time you take a measurement, holding the probe at the same angle each time. Make a measurement even when the intersection is covered by an electrode.

Note: If your pattern is symmetrical, you can use this symmetry to limit the number of data points you collect to a half or a fourth of the total pattern. If you have any doubts, ask your instructor.

7. When finished with the measurements, disconnect the battery and turn the DMM off. Return the lab materials to a place specified by your instructor

## Setting up Excel for Electric Fields

• Use the mouse to select all of the data, including the labels for the x and y axes (shaded area on drawing above). Only select the labels on top and on the left side of the data sheet.
• Click on the Chart Wizard.
• Drag the mouse to create a box on your spreadsheet.
• Click the Next box.
• Select the 3-D Surface and click Next.
• Select option 1 and click Next.
• Click Next for the screen that asks about data series.
• Select No for the "Add a Legend" question.
• Type a chart title that includes your group's class period.
• Leave the X and Y axes titles blank, but enter Volts for the Z-axis title.
• Click OK

## Change the View

1. Once you have the graph drawn, rotate it until you get the best representation of the electric field contours. Print this view.

2. Rotate the graph until you are looking straight down on top of it, showing just the x and y-axes. Print this view.

## Written Assignment

Write a short description of what these two views of your electric field show about your electric field and how they show it. Print that description, including your group's names and the class period, and attach it to the graphs before submitting.

Updated 4/4/02