Exploring Electric Potential Activity using EM Field - Modeling Physics

Electric Potential Model:
Exploring Electric Potential
To Accompany "EM Field" Software
(See the worksheet on Field for suggestions on how to use the EM program.)
Exploring potential around a point charge
Place a positive "8" charge in the middle of your screen. From the "Field and Potential" menu,
select "Potential."
1. Click your pointer at several positions around the point charge.
a) What do you notice about the value of potential as you move away from the charge
b) Why is only a value given for potential Why isn’t a directional arrow given as well
2. Release the mouse: this will leave a potential value on the screen.
a) How can you create four identical values Test your prediction.
b) What relationship might exist between potential and distance from the point charge Test
your prediction.
c) Erase the potential values. Go now to the "Field and Potential" menu and select
"Equipotential lines." Click on the screen around the charge to create lines which represent
positions of equal potential.
i - Why are all the lines circular
ii - Where would you find the line representing 0.0 volts
3. Erase the equipotential lines and replace the positive charge with a negative "8" charge.
a) Predict how the values of electric potential around the negative charge will be the same as
those around the positive charge. In what ways would you find them different
To test your prediction, you will have to go back to the "Field and Potential" menu and select
"Potential".
b) How are lines of equal potential around the negative charge different from those around a
positive charge
c) Where does the program assign the line representing 0.0 volts around a negative charge
©Modeling Workshop Project 2009 1 E&M Unit 2 – Exploring Potential

4. Erase the markings on the screens. Place a positive "4" and a negative "4" charge on the screen
about 8 centimeters apart.
a. Use the "Potential" values option to determine what the potential is at various locations around
the two charges. After completing your exploration, answer the following questions:
i - At what place or places is the largest positive value of potential found
ii - At what place or places is the largest negative value of potential found
iii - At what place or places is the potential zero
iv - Describe as best you can the general pattern of potential values.
b. Draw lines below representing places of equal potential: you should draw four or five such
lines, including the line representing places where the potential is 0 volts. If you like, use the
"Equipotential" option in the program to help you complete your diagram.
i - Looking at the diagram you have just created, would there be an energy transfer if a
positive charge were moved from point B to point A into or out of the field
ii - On your diagram above, make a heavy line representing a path along which a negative
charge could be move without losing or gaining potential energy; mark this line “Energy
Free Path.”
5. Erase all markings. Leaving the positive "4" charge in place, replace the negative "4" charge
with a second positive "4" charge.
a. Use the "Potential" values option to determine values of the potential around the two charges.
After completing your exploration, answer the following questions:
i - Where is the value of potential 0 volts
©Modeling Workshop Project 2009 2 E&M Unit 2 – Exploring Potential

ii - Describe as best you can the general pattern of potential values.
iii - If you placed a small positive charge halfway between the two positive "4" charges, how
would it move
iv - Would a transfer of energy be required to move a small positive charge towards the
positive charges Explain.
v - Would a transfer of energy be required to move a small negative charge towards the
positive charges Explain
b. Draw lines below representing places of equal potential: you should draw four or five such
lines, including the line representing places where the potential is 0 volts. If you like, use the
"Equipotential" option in the program to help you complete your diagram.
©Modeling Workshop Project 2009 3 E&M Unit 2 – Exploring Potential

Exploring potential between parallel plates
Open the file “2 plates.emf” Select "Equipotential Lines" from the "Field and Potential" menu
and determine where the lines of equal potential lie between the two plates. Make a diagram of
your results below:
Answer these questions based upon your explorations:
a) How does the potential vary as you move from the middle of the positive “plate” to the
middle of the negative “plate”
b) Suppose you placed a small positive charge close to the positive “plate” (for example, at
point "Z" on the diagram).
i - Describe the change in potential energy as the charge moves toward the negative “plate”.
ii - Describe the change in kinetic energy as the charge moves toward the negative “plate”.
iii - As the charge moves, is energy transferred into or out of the electric field
©Modeling Workshop Project 2009 4 E&M Unit 2 – Exploring Potential