Name _________________________________________ Date ____________________ Period ____________
Electric Potential of a Parallel Plate Capacitor
Objective: To apply the concepts of electric potential and electric fields to a parallel plate capacitor.
Reasoning about the inside of a capacitor (or the region between two parallel plates) is an important AP
Physics 2 skill. This lab will help students understand the differences in potential within the capacitor through
several conceptual representations. Students will present a plot of electric potential vs. distance across the
capacitor, a sketch of equipotential surfaces within the capacitor, a contour map for the capacitor, and an
elevation graph for the capacitor.
Setup:
Step 1: Obtain a laptop and login to Logger Pro. Connect a USB cable from a Vernier Lab Quest to the laptop,
and attach the differential voltage meter to the Vernier Lab Quest.
Step 2: Obtain a ripple tank and fill with approximately 1 cm of water. Place two aluminum plates into the
ripple tank parallel to one another (as shown below). Attach a positive and negative alligator clip from the
battery to each aluminum plate. Important Note* - The Vernier differential voltage meter only measures a
voltage range of 0-6.5V. This means the battery cannot exceed 6V if you are using Vernier equipment. If
you’d like to use a 9V battery, you must use a multi-meter to measure the potential.
Step 3: Ground the differential voltage meter to the negative plate. Use the positive lead of the differential
voltage meter to measure the potential between the plates of the capacitor.
Step 4: Create a grid system (graph paper recommended) that can be used to collect potential values at
various locations. Remember that the data collected will later be used to create a graph (Be sufficient). Each
student should create his/her own grid sheet. After the grid is created, place it underneath the ripple tank and
in between the two parallel plates.
Data Collection:
Step 1: Model the potential difference within a capacitor by creating the schematic of the capacitor on your
grid sheet. Note – Since the grid paper is below the ripple tank, either create a data table, or use another lab
partner’s grid to record data. Important Note* - Use the zeroing button just to the left of the green collection
button in Logger Pro for more accurate data collection. In order to zero, you must touch the red and black
leads of the differential voltage meter to the same aluminum plate. The final step is to click the zero button.
Data Analysis:
Step 1: Draw five equipotential lines on the grid paper at 0.5V, 1.0V, 1.5V, 2.0V, 2.5V (if using 3V of batteries).
Step 2: Draw at least five electric field lines on the grid paper (Use a different color for the field lines).
Step 3: Use your collected data and Excel to create an elevation graph of potential vs. position. Plot the
function on the graph.
Conclusions:
1. When you plotted out the equipotential lines on your grid, what did you notice about the spacing of
the equipotential lines? What assumption can be made from this spacing observation?
2. What direction does the electric field point? What did you notice about the potential as you moved
the positive lead closer to the negative aluminum plate?
3. How were the electric field lines drawn in relation to the equipotential lines?
4. If you could move an individual positive charge by hand, what would you have to do to move the
charge from the negative plate to the positive plate (describe in terms of work and energy)?
5. If you could move an individual negative charge by hand, what would you have to do to move the
charge from the negative plate to the positive plate (describe in terms of work and energy)?
6. State the relationship between the potential and position variables. ______________________
What is the meaning of your slope (show evidence)? Record the value of your slope.
7. Relate the idea of moving a charge around the field (questions 4 & 5) to the significance of the slope of
your elevation graph.