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Name _______________________
Measuring E-Fields in Conductive Paper
The purpose of this assignment is to introduce 2 new tools and strengthen understanding about
the connection between electric fields and electric potential.
I. The Power Supply
Our Extech Power supplies have digital
Voltage
readings of Voltage and Current output.
When using the power supplies,
Current
A. the power should remain off until
the circuit is completed.
B. the voltage output should be set to
0.0 V
C. the current output should be set to
½ maximum
Ground
+V
When the circuit is complete, then
A. turn the power on
B. slowly increase the voltage to the desired setting
C. turn the power off if the current goes too high or if there is smoke or you smell
something burning.
II. The Digital Multimeter (DMM)
The DMM is a powerful tool that can make many kinds of measurements. We will be measuring
potential difference or voltage in this activity. Move the selector to 20 V (or 200 V).
Switch from Alternating
Current to Direct Current
Screen Tilts Up
On/Off
Range for Voltage
Range for Resistance
20 V
Range for Current
Red Lead Stays Here for Voltage and
Resistance Measurements
Red Lead Moves Here for
Current Measurements
10 A
DMM probe
2 A or less
DMM ground lead
III. Experiment
Part 1 – 20 cm Strip @ 10V
Connect the power supply
leads as shown above and
apply 10 V to each end of
the 20 cm strip.
Distance
above Ground
(cm)
Electric
Potential (V)
Place the 20 cm strip on a
piece of cardboard.
Connect the DMM ground
lead on the ground end of
the carbon strip.
Place the DMM probe at
the appropriate distance
on the carbon strip and
measure the electric
potential for each
distance above ground.
Electric Field
Strength
(V/m)
Distance
above Ground
(cm)
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
Plot the electric potential as a function of position on the attached graph paper.
Calculate the average electric field strength:
E
V V
V
 2 1
x
x2  x1
Part 2 – 6 cm Strip @ 10V
Repeat the steps above for the 6 cm strip.
Electric
Potential (V)
Distance
above Ground
(cm)
Electric Field
Strength
(V/m)
Distance
above Ground
(cm)
6
5
4
3
2
Part 3 – 6 cm & 14 cm Strip @ 10V
Repeat the steps above for the 6 cm strip and 14 cm strip connected sequentially with a
connecting lead.
Distance
Electric Field
Distance
Electric
above Ground
Strength
above Ground
Connect the power supply
Potential (V)
(cm)
(V/m)
(cm)
leads as shown above and
20
19
apply 10 V to each end of
the connected strips.
18
17
Place the strips on a piece
of cardboard.
Connect the DMM ground
lead on the ground end of
the carbon strip.
Place the DMM probe at
the appropriate distance
on the carbon strip and
measure the electric
potential for each
distance above ground.
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
Plot the electric potential as a function of position on the attached graph paper.
Calculate the average electric field strength:
Connecting lead
E
V V
V
 2 1
x
x2  x1
Part 4 – Conclusions
1. How is the electric field strength reflected by the graph above?
2. What happens to the electric potential of the charges as they migrate through the
conductive paper?
3. What is the potential difference of the charges between the ends of the connecting
alligator lead in part 3?