Download Physics Lab Graphing Equipotentials and Lines of Force of Electric

Name________________________________________ Date__________ Partner(s)________________________
___________________________
Physics Lab
Graphing Equipotentials and Lines
of Force of Electric Fields
In this laboratory exercise, the positions of equipotentials for three different electrode configurations are
found by measuring voltages using a multimeter. The three configurations are: 1) two electrodes
simulating two point charges of opposite sign, 2) two parallel line electrodes simulating charged parallel
plates, and 3) a circular electrode and line electrode simulating a charged cylinder and plate. Knowing
the positions of the equipotentials, we can draw the electric field lines of force.
Materials:
Equipotential plotting kit: 3 sheets of conducting paper with different electrode designs
6 push pins
2 wires with ring connectors
DC power supply
Digital multimeter with leads
3 sheets of graph paper
3 leads (2 black, 1 red)
2 alligator clips
Diagram: The drawing below shows the experimental arrangement when the equipotentials for the
cylinder and plate are to be found.
multimeter
DC power
supply
red lead
with probe
electrode
probe
electrode
black lead
black lead
red lead
Procedure:
1.
Pin one of the conducting papers to the corkboard with four push pins.
2.
On your own sheet of graph paper, draw the positions of the electrodes, showing accurately where
they are located and their size and shape.
3.
Set up the equipment and make the connections as shown in the diagram above. Be sure there is a
good electrical contact between the wires and the electrodes.
4.
Set the multimeter to read DC Volts from 0-20 volts. Touch the probe to the electrode that is
connected to the negative terminal (black) of the DC power supply. The reading on the multimeter
should be zero. If it is not, then make sure there is good contact between the wire, the push pin, and
the electrode drawn on the paper.
5.
Now touch the probe to the other electrode and adjust the DC power supply until the voltage on the
multimeter reads 12 volts. Make sure there is good contact between the wire, the push pin, and the
electrode drawn on the paper.
Note: By applying voltage between the two electrodes, we have created a situation where the 12volt
electrode simulates an electrode with positive charge, and the 0 volt electrode simulates an electrode
with negative charge.
6.
Hold the probe vertically and lightly touch various points on the conducting paper. Notice that the
reading on the multimeter changes. These values indicate the electric potential (the “voltage”) at the
various points you probed.
7.
Use the probe now to find a position on the conducting paper where the voltage is 2 volts. Record
this position on your graph paper. Continue to record points corresponding to 2 volts until enough
points are located so that a smooth curve can be drawn through the points without too much
extrapolation. Repeat the measurements described above for 4, 6, 8, and 10 volts. (When measuring
the plate and ring configuration, be sure to measure inside the ring.)
8.
Repeat the above steps for the remaining two conducting papers with the different electrode
configurations.
Analysis:
1.
Each member of the group will use the data from a different electrode configuration to draw the
equipotentials and the lines of force.
2.
Use a pen or pencil to draw smooth curves through the points that correspond to the equipotentials.
Label them with their respective voltages. Because the conducting paper is not uniform, your
smooth line may not pass through all the points that correspond to a specific voltage.
3.
Use a different color pen or pencil to draw the lines of force of the electric field, and be sure to
indicate the direction of the electric field.
4.
When the three drawings are completed to the satisfaction of the group members, staple them to the
back of these laboratory instructions.
Things to keep in mind:
1.
What is an equipotential, and what units are used to describe the values of the equipotentials?
2.
In this experiment, what equipment did you use to find the values of the equipotentials?
3.
The equipotentials and lines of force of the electric field are perpendicular to each other when they
cross each other. How do you know that they should be perpendicular?
4.
When the lines of force of the electric field meet the surface of a conductor, the lines should be
drawn perpendicular to the surface of the conductor. Why should they be perpendicular?
5.
What is the value of the electric field at all points in and on all of the 12 volt electrodes? Why?
e.g., point
E=?
plate
ring
6.
What should be the value of the electric field inside the circular electrode? Why?
E=?