ELECTRIC FIELD AND ELECTRIC POTENTIAL VI
DEBRA JONES
PARTNER: JULIA JONES
MARCH 2, 2015
PHYSICS-205-004
Abstract:
In this experiment, a Digital Voltmeter was used to find the equipotential lines of four
different electric fields. On a sheet of black conductive paper, a parallel plate capacitor, a point
source and guard ring, a dipole, and a Mickey Mouse shape was drawn using CircuitWorks
Nickle Conductive Ink. For each shape, the field lines and equipotential were predicted. For the
parallel plate capacitor, it was predicted that the field lines would move from the positive to the
negative line, and that the equipotential lines would radiate out from both lines. For the point
source and guard ring, it was predicted that the field lines would move out from the dot and stop
at the ring while the equipotential would do the same (in ring form). For the dipole, it was
predicted that the field lines would point away from each point, and that the field lines would
start as small circles around the point, but would then radiate out until they merged and formed
larger ovals around both points. For the Mickey Mouse shape, it was predicted that the fild lines
would move out from the center point and end on the Mickey Mouse shaped outside border, and
the equipotential lines would radiate out in rings. It was predicted that the further from the center
they got, the more they bent to resemble the shape of Mickey Mouse until they stopped at the
border.
After the predictions were made, two metal push pins were inserted into each of the
shapes and were connected to a power supply so that there was a potential difference of 28 V
between the two electrodes. The Fluke Digital Multimeter and two probes were then used to map
the equipotentials for the parallel plate capacitor, point source and guard ring, a dipole, and a
Mickey Mouse shape. For the parallel plate capacitor, the 4 V equipotential line was found to
arc above the top plate, the 8V line was found right below the top plate, the 12-14V line was
found directly in the middle of the two plates, the 20 V line was found directly over top of the
bottom plate, and the 24 V line was found to arch below the bottom plate. For the point source
and guard ring, the lines were found to radiate out in circles that successively became large. The
closest ring was 21 V, followed by a 10 V ring, a 5 V ring, and 0 V outside of the border. For the
dipole, on the left point, there were two small circles that were 11 V and 14 V respectively, while
on the right point, the two circles were 17 V and 18 V. Surrounding the points and their smaller
circular equipotential lines was a large oval that was 15 V. For the Mickey Mouse shape, there
was a small ring around the central point that was 12 V. As the rings moved towards the outside,
they began to adopt the shape of Mickey Mouse. Each ring looked more like Mickey than the last
and were found to be 6V, 2 V, and 1 V moving from the inside to towards the border. Outside
the border was 0 V. Based on the data obtained, the predictions were very similar to the results.
However, a potential source of error could have been that the metal push pins did not have full
contact with the conductive ink. This would cause the readings to be different.
Discussion:
1) A) The electric potential is most positive at the guard ring.
B) The electric potential is most negative at the center point.
C) Outside the guard ring, the electric potential is zero. It does not vary.
Electric Potential vs Distance
4
Electric Potential (V)
3.5
3
2.5
2
Electric Field
1.5
Linear (Electric Field)
1
0.5
0
-800
-600
-400
-200
0
Distance (cm)
2) A)
B) Ex= -V2-V1/x2-x1= -14 V-0V/.02 m- 0m= -700 V/m
Electric Field vs Midpoints
0
Electric Field (V/m)
-100
0
1
2
3
4
-200
-300
-400
Electric Field
-500
-600
-700
-800
Midpoints (cm)
C)
D) ΔV= -EΔx = -(-700 V/m)(.06 m) = 4200 V