Many of us have grabbed two pieces of aluminum foil and a paper towel, quickly sandwiched them together, and exclaimed in lecture, “Look! It's easy to make a capacitor!” Then we move on from there, calculating things such as capacitances with various dielectrics or plate sizes, the capacitance of capacitor networks, RC circuits, etc. We typically do these calculations with capacitance values that are far removed from what we just created in our quick demonstration of a capacitor. Students might justifiably question whether the capacitor that we blithely made has any relation to the values that we are using in our calculations. It may be useful to investigate the quality of such handmade capacitors so that our students get a more intuitive feel for these ubiquitous electrical components.

1.
Bob
Froehlich
, “
A demonstration condenser microphone
,”
Phys. Teach.
50
,
508
(
Nov. 2012
).
2.
William
Ennis
, “
A simple, successful capacitor lab
,”
Phys. Teach.
49
,
272
(
May 2011
).
3.
Frank
Noschese
, “
Tin foil capacitor
,”
Phys. Teach.
48
,
621
(
Dec. 2010
).
4.
J. D.
Cutnell
and
K. W.
Johnson
,
Physics
, 9th ed. (
Wiley
,
Hoboken, NJ
,
2012
).
5.
An Extech EX430 was used for the measurements in this paper. Several models capable of measuring capacitances in the pF range are available for under $50.
6.
An inexpensive source of electrolytic capacitors is the Jameco (http://www.jameco.com/) “grab bag” of 100 assorted capacitors.
7.
A. J.
Diefenderfer
,
Principles of Electronic Instrumentation
, 3rd ed. (
Saunders
,
New York
,
1994
).
8.
T. T.
Grove
,
M. E
Masters
, and
R. E.
Miers
, “
Determining dielectric constants using a parallel plate capacitor
,”
Am. J. Phys.
73
,
52
(
Jan. 2005
). Ehis is one example of many articles for more sophisticated experiments with capacitors.
9.
Like so many physicists, the author first learned of the electrical properties of pencil lead from the Forrest
M.
Mims
 III
booklet Science and Communication Circuits & Projects
(
Master Publishing
,
Niles, IL
,
2004
).
10.
Marcos Alfredo
Salami
,
João Bernardes
da Rocha Filho
,
Cláudio
Galli
, and
Rita de Cássia
da Costa
, “
Capacitors made by drawing with graphite on paper or plastic
,”
Phys. Teach.
45
,
392
(
Sept. 2007
).
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