Physics 42 Lab: Capacitance and Dielectrics
The purpose of the lab is to explore the properties of a parallel plate capacitor with and
without a dielectric. We will test the theoretical prediction for the capacitance of a
capacitor and how capacitance depends upon plate separation distance.
For a parallel plate capacitor with surface area A, plate separation distance d, dielectric
constant , the capacitance, C is predicted to be:
C
 0 A
d
where the permittivity of free space is given as:
 0  8.85x1012 C 2 / Nm2
Equipment: 2 Parallel Plate Capacitors, 1 Multimeter, 4 alligator clip cables, 2 wires for
measuring capacitance, various sheets of dielectric materials, 1 clear plastic ruler
Part 1: Capacitance vs. Plate Separation
Set up the capacitor with the multi-meter as shown by your instructor. Make a data table
in excel being sure to label everything including units on the measurements. Measure the
diameter of the capacitor. Measure the capacitance for at least 10 separation distances,
starting at 1.00 cm. Calculate the capacitance using the theoretical equation for each of
these distances assuming the dielectric constant for air is 1.00059. Put the calculated
values in a column next to the measured values. Calculate the percent difference between
theory and experiment for each measurement, and find the average error for all
measurements. Plot capacitance vs plate separation distance. Analyze the graph using an
appropriate fit and discuss your results. Does your result agree with the theoretical
prediction?
Part 2: Capacitance with Dielectrics
Select three different dielectric materials to test. You need to find a plate separation
distance that you can hold constant for the different materials, in order to compare the
capacitance, so play around with the materials and find a distance that will work. It will
not be exact but try to get the distances as close to each other so you can do a qualitative
comparison. Put the distances in a table for each material along with the measured
capacitance. From the capacitance equation, calculate the dielectric constant for each
material. Go online and find a website that lists the constants. What materials have
dielectric constants closest to watch you found? Make sure you include the website URL
and the name and dielectric constant values you found online. Get a percent difference
between what you found online and what you measured. Briefly discuss your results and
how the different materials compared.
Part 3: Capacitance in Parallel and in Series.
Set the plate separations for two capacitors and calculate and measure the individual
capacitance of each capacitor alone. Calculate the predicted equivalent capacitance for
the two in parallel and in series using the following relationships.
Capacitors in Parallel:
V  V1  V2
Ceq  C1  C2
Capacitors in Series:
V  V1  V2
1
1
1


Ceq C1 C2
Show your calculations. Hook up the capacitors in parallel and in series and measure the
total capacitance of the system. Use a second multimeter to measure the voltages across
each capacitor and the total voltage of the system. Calculate the percent differences
between your calculated and measured results and put all the data in your data sheet.
Briefly discuss your results.
Your lab report should include a brief abstract at the start of your report which
summarizes results.