Make Your Own Capacitor
OBJECTIVE: To construct a capacitor from common items, estimate its capacitance using a standard formula, and
confirm its value with a capacitance meter.
APPARTUS:
Aluminum foil and scissors
Meter stick
Printer paper
roll of wax paper
capacitance meter
2 kg mass
physics textbook
INTRODUCTION:
One way to understand how something behaves is to build a working model of it. In this lab you will gain insight into the
behavior of a capacitor by making one. A capacitor is composed of two conductors separated by an insulator or a
dielectric. Typically, the two conductors have an equal area. When charged, each conducting sheet of the capacitor holds
the same magnitude of charge but of different sign, one sheet positive, and the other sheet negative.
The formula for the capacitance, C, of a parallel plate capacitor is:
C
0 A
d
Equation 1
In this lab you will construct a capacitor and predict its capacitance based on the above formula. To predict its value, you
must take measurements of the relevant materials you use to construct the capacitor. The dielectric constant for wax paper
is: κ = 2.0. The thickness of the printer paper is 0.000094 m and the wax paper 0.000033 m this will be d in the above
formula. After your capacitor is constructed and you have a numerical prediction for its value, you may then measure the
capacitor's value with a "cap" meter provided by your instructor and compare the results.
PROCEDURE:
1. Use a standard piece of printer paper to provide the spacer for your capacitor.
2. Now cut two equal lengths of aluminum foil (a little larger than your physics textbook). Make the widths of the
aluminum foil also shorter than the printer paper to insure that the plates do not touch. The two sheets of aluminum foil
should have the same physical dimensions (length and width) so that their areas are equal. Measure these lengths and
widths for each of the two aluminum foil sheets precisely with a meter stick and calculate the area of each sheet. Use units
of square meters.
3. Lay down one sheet of foil on the table. Now lay down a paper sheet on the foil sheet and finally the second piece of
foil on top of the printer. Make sure that the two pieces of foil do not touch one another as this will "short" out your
capacitor.
4. Place your textbook on top of the capacitor. Place the 2 kg masses on the textbook to flatten the capacitor. Now that
your capacitor is complete, test it to make sure it’s working by measuring its capacitance value with the meter. Turn the
dial to measure capacitance and touch a probe to each of the plates.
5. Replace the printer paper spacer with a piece of wax paper and measure capacitance with the dielectric wax paper as a
spacer.
1
Make Your Own Capacitor Lab Sheet
DATA TABLE: INCLUDE ALL UNITS
Foil
Length
Dielectric Constant (κ)
Width
Measured Capacitance
Area
Printer Paper
1.0
Wax Paper
2.0
CALCULATIONS: SHOW ALL WORK
1. Calculate the capacitance for each setup using equation 1.
2. Using percent difference compare the measured value from the capacitance meter to the calculated value for each
setup.
3. Calculate the dielectric constant of the wax paper by using the definition of the dielectric constant in your
textbook.
RESULTS TABLE: INCLUDE ALL UNITS
Calculated Capacitance
% Difference
Calculated Dielectric
Wax Paper
Printer Paper
Conclusion: Comment on the agreement between the estimated and measured values. State any reasons how the
agreement could be improved in future attempts. Are there any systematic errors in the procedure? Could they be
eliminated or minimized? What would be worse during the construction phase, puncturing the aluminum foil or the
dielectric?
TURN IN: LAB SHEET
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