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Mapping Electric Fields Lab
©Modeling Workshop Project 2007
1
E1-Charge&Field Mapping E-Field v3.1 JBS

Electric Charge Behavior and Interactions Model:
Mapping Electric Fields Lab

In the lab you will look at the electric force on an "electrostatic compass" and use your
observations to identify the key properties of the electric field. You will specifically look at the
electric field created by a single "-" charge, a single "+" charge, two unlike charges, two like
charges, and a single "-" charge and a conducting sheet.

Lab materials:

[] ring stand with rod clamped horizontally,
[] two PVC rods with string handles
[] one aluminum foil-covered rod with string handle
[] wool sock
[] roll of magic tape
[] thread tied to straightened out paper clip
[] 4-5 pieces of 8.5" x 11" paper.

For each part of the lab, the setup will be involve
variations of the setup shown in the diagram on the right:




Making an electrostatic compass:
We have seen that pulling tape off of a surface leaves the tape with a net charge. Using
oppositely charged tapes, we can make a "compass" where one tape is attracted and the other is
repelled from a charged object.
A. Put a 10 cm long base tape on the table with a folded under handle.
B. Place two more tapes on the first. With a pen, label the handle of the middle tape "-" and the
handle of the tape on top "+".
C. Slowly remove the top two tapes together, and then make sure they are not charged by firmly
rubbing the slick side of the tape.
D. Briskly separate the two tapes, and sticky side up, overlap the edges of the tapes
as shown. (Avoid excessive contact with the tape since this will discharge it.)
E. Draw an arrow across the tapes from the "-" side to the "+" side as shown.
F. Attach the center of the tapes to the straightened out paper clip so the string
extends upward from the handles. (See the first picture in this lab.)

Depending on the humidity, you will need to recharge your tapes periodically by repeating steps
C, D and F.
©Modeling Workshop Project 2007
2
E1-Charge&Field Mapping E-Field v3.1 JBS

Part 1. The electric field due to a negatively charged object

1. Hook the PVC pipe's string handle over the horizontal bar from the ring stand.
2. Charge the pipe by rubbing it with wool.
3. Place a piece of 8.5" x 11" paper on the table below the pipe.
4. Draw a circle on the paper directly below the pipe (as viewed from over the table) and write a
"-" inside the circle to indicate the pipe's charge.
5. Make sure your electric compass is charged and operational, if
not, follow the steps to recharge it.
6. Start with the electric compass very close to the PVC pipe.
Draw an arrow on the paper directly below the arrow on the tape.
7. Now move the electric compass farther from the pipe so that the
new arrow you draw meets head-to-tail with the last arrow you
drew. Continue until your arrows go off the edge of the page.
8. From three other starting points near the PVC pipe, map the
electric field.
9. Save your electric field map and sketch your observed electric
field in the box on the right.

Part 2. The electric field due to a positively charged object

1. Put a clean sheet of paper on the table.
2. Remove the PVC rod, and hang a foil-covered rod in its place.
3. Charge the foil rod by induction: bring a charged PVC pipe near
the foil rod and then touch the foil with your finger. Put the PVC
pipe away and use your electrostatic compass to verify that the foil
is positively charged.
4.Now follow steps 4-8 above to map the electric field. (Be sure to
label the circle for the foil rod "+".)
5. Save your electric field map and sketch your observed electric
field in the box on the right.

Questions for parts 1 and 2:

1. Where do the electric field lines begin?


2. Where do the electric field lines end?


3. How many other electric field lines could you have drawn?
©Modeling Workshop Project 2007
3
E1-Charge&Field Mapping E-Field v3.1 JBS

Part 3. The electric field due to objects with unlike charges.

1. Hang the foil covered rod and the PVC pipe on the horizontal bar so that they are about 15 cm
apart.
2. Place two pieces of 8.5" x 11" paper on the table below the pipes and tape their edges together.
3. Draw circles on the paper directly below the pipes and label their charges.
4. Recharge your electrostatic compass.
5. Charge the PVC by rubbing with wool.
6. Charge the foil rod by induction.
7. Map the electric field as before, starting from the foil-
covered rod. Draw enough field lines until you think you could
predict where every field line would go from any starting point
around the rod.
8. Check with your teacher before you continue.
9. Save your electric field map and sketch your observed
electric field in the box on the right.

Part 4. The electric field due to objects with like charges

1. Hang two PVC rods on the horizontal bar so that they are about 15 cm apart.
2. Place two new pieces of 8.5" x 11" paper on the table below the pipes and tape their edges
together.
3. Draw circles on the paper directly below the pipes and label
their charge.
4. Recharge your electrostatic compass.
5. Charge your rods.
6. Map the electric field as before, always starting from a rod.
Draw enough field lines until you think you could predict
where every field line would go from any starting point around
the rod.
7. Check with the teacher before you continue.
8. Save your electric field map and sketch your observed
electric field in the box on the right.

Questions for parts 3 and 4:

1. Where do the electric field lines begin?

2. Where do the electric field lines end?

3. How many other electric field lines could you have drawn in each part?


4. Do the field lines ever cross? Explain why this must always be so.
©Modeling Workshop Project 2007
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E1-Charge&Field Mapping E-Field v3.1 JBS

5. Predict what the electric field due to two "+" charges by drawing a number of electric field
lines below. Put arrows on your electric field lines.

















Part 5. The electric field due to a negatively charged object near a conducting sheet

1. Attach an aluminum foil sheet to a book stood upright or another suitable fixture. Once you
have positioned the foil, be careful not to touch it so that you know the net charge on the foil is
zero.
2. Place the PVC rod about 15 cm from the foil sheet and charge the rod.
3. Map the field between the rod and the aluminum sheet. Draw enough field lines until you
think you could predict where every field line would go from any starting point around the rod.
4. Save your electric field map and sketch your observed electric field in the box below.

©Modeling Workshop Project 2007
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E1-Charge&Field Mapping E-Field v3.1 JBS

Questions for part 5:
1. At what angle do electric field lines meet the conducting surface? What would happen to
electric charges at the surface of the metal if the field lines did not meet the surface at this angle?







2. Based on your understanding of the motion of electric charges in materials, draw a likely
charge distribution on the aluminum sheet that produced the field you observed.



3. Where must electric field lines start and end?



4. Carefully draw some electric field lines on your diagram above taking into account your
answers for questions 1 and 3.

5. The field lines you have drawn for part 5 look almost exactly like the drawing you made in
what other part of the lab?



a. How are they the same?




b. How are they different?