Phys 202
Mapping Electric Field Lines and Equipotential Surfaces
Purpose: You will perform several experiments illustrating the concept of electric potential.
Equipment: 1 conducting paper sheet, 1 wooden board, 1 power supply, 1 voltmeter and 1 graph paper sheet.
Mapping Electric Field Lines and Equipotential Surfaces
1)Setting up the experiment:
a)Place a black sheet of conducting paper onto the wooden board provided and hook up the power source, one lead to each metal clip on the board as pictured below.
This set up is intended to "mock" two electric point charges. Each one of the circular areas of the silver paint will be called (for lack of anything better) the "positive charge" and the "negative charge". The positive charge is the one hooked up to the higher potential and the negative charge is the one hooked to the low potential side of the power source.
b)Set your power supply at about 6 volts, so that the voltage difference between the two circular regions of the silver conducting paint is exactly 6 volts. To measure the voltage difference between the two circular regions of the silver conducting paint, place the black probe on the “negative charge” and the red probe on the “positive charge”. You will probably need to press firmly, but don't ruin the paint job.
2)Taking data
a)Leave the black probe stationary on the lower potential (on the negative charge) and move the positive probe from dot to dot, measuring the potential difference between the black probe and the red probe (Try at least 10 different dots).
Record these voltages on the graph paper provided.
DO NOT DRAW ON THE BLACK CONDUCTING PAPER
b)Drawing the equipotential lines
Pick a particular voltage and try finding all the points on the black conducting paper, which are at that same voltage. Mark all of these points on your graph paper. Do not restrict yourself to just checking at the dots. Check in between the dots as well.
Once you have enough points, connect the data points with a line on your graph paper. This line represents all positions with equal voltage. We call this an “equipotential line” or “line of equal potential”.
Try tracing out 4 or 5 different equipotential lines for 4 or 5 different voltages in approximately 1V increments. Draw each of these lines in on your graph paper in a different color.
Note: Because we are working in a plane, we get equipotential lines. In 3D, we would get equipotential surfaces.
c)Drawing the electric field lines
Now, that you have a map of the equipotential lines, you will sketch in the electric field lines.
Recall the rules stated in class:
(1)A field line starts either at infinity or on a positive charge.
(2)A field line ends either at infinity or on a negative charge.
(3)Field lines are perpendicular to equipotential surfaces
Using these rules, draw the field lines on your graph paper. Mark on your graph the name of such a field distribution.
3)Repeat the procedure above (in 2) for the conducting black paper as pictured below.
4)Calculating the electric field
The value of one component of the electric field at any point is equal to
where x is any specified direction and Ex is the component of the electric field in that direction.
a)Calculate the strength of the electric field at several different positions for the configuration studied in 3) above. Make sure to give sample calculations.
b)Is the field strength uniform between the two plates?
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