Download Electric Field Mapping

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.