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Electric Field Mapping (Cadiz Physics 2014) Purpose: To map electric fields which exist in the space around charged bodies. To understand the relationship between electric fields and lines of equipotential. To study the use of a galvanometer to find lines of equipotential. Theory: An electric field exists in the space around any charged body. Any charge placed in this field will experience a force tending to move it. The direction of the electric field at any point is the direction a positive charge would tend to move if placed at that point. In any electric field there are many points having the same potential. These are called equipotential points, and the line connecting these points is called an equipotential line. A line of force is the path that a free test charge would follow in traversing an electric field and lines of force are everywhere perpendicular to equipotential lines. It is usually easier to determine the equipotential lines in an electric field than the lines of force, but since these sets of lines must everywhere be normal (perpendicular) to one another, if one is known the other is readily constructed. This is illustrated in the figure below. If a potential difference is established between two points on the conducting paper an electric field is set up in the paper. The object of this experiment is to plot the electric fields for several electrode configurations by determining the equipotential lines (dotted lines) and then drawing the lines of force (solid lines). Procedure: (Your work will be graded on neatness and accuracy) 1. Form groups of two or three. 2. Select a sheet of the conducting paper having the imprinted electrodes and place it on the mounting board with the silver push-pins touching the silver electrode configuration. 3. Set up the desktop power supply so that approximately 5 volts and 3 mA show on the digital readout. (A DC battery may be substituted.) Connect the terminals to the pushpins at the end of the imprinted electrodes. 4. Locate the galvanometer probes so that one probe touches the conducting paper between the electrodes along one side of the coordinate system. Record this position using the grid markings. Move the other probe over the paper to find a different point giving a zero reading on the galvanometer. Zero readings indicate points of equipotential. Record the location of several points where the reading is zero so that you can connect the points with a smooth line. These lines are equipotential lines. 5. Repeat step 4 several times so that the equipotential lines are determined for the entire grid (say 4 - 5 lines with 10-20 points per line). Work quickly. 6. Connect the dots with a dotted line using a French curve, 7. Repeat steps 3-6 for each of the three different electrode configurations. 8. Construct the Electric field lines using solid lines. Remember, electric field lines must be perpendicular to surfaces and equipotential lines and never cross. 9. Use the multi-meter to take readings on the electrode configurations. You should take note of the values of voltage drops (i.e. “electric pressure” or potential difference… all synonyms) 10. Bonus: Color code (Red Orange Yellow Green and Blue) your electric field using the concepts of the CASTLE curriculum where higher electric pressure is indicated with red and lower electric pressure is indicated with blue Report: Each member of your group should take a turn mapping the equipotential points, drawing the equipotential lines, and constructing the electric field lines. One report is required per group. The report should consist of your data sheets and your graphs. Work together as a team to move things along swiftly.