In this work we describe a simple setup for measuring electrostatic charge and polarity in electrostatic experiments. This low-cost detector only requires a graphite pencil, a capacitor, two switches, and a voltmeter, and holds the promise of transforming qualitative activities that are commonly used to teach electrostatics into quantitative activities. In order to measure the charge and polarity of charged objects, a pencil is used as an antenna to collect charge from the object under study. The collected charge is transferred to a capacitor, and the resulting voltage at the capacitor is measured using a voltmeter. In contrast to other devices, our detector can be used to measure the amount of charge stored in objects at several thousand volts, as for example Van de Graaff domes.

1.
Xiang
Yong Chen
and
Xing
Wang
, “
Detecting the polarity of an electric charge
,”
Phys. Teach.
37
,
344
(
Sept.
1999
).
2.
James
Lincoln
, “
Devices that can identify positive vs. negative charge
,”
Phys. Teach
55
,
440
(
Oct.
2017
).
3.
Mihai P.
Dinca
, “
Charge sniffer for electrostatic demonstrations
,”
Am. J. Phys.
79
,
217
221
(
Feb.
2011
).
4.
Hakan
Isik
, “
An instrumental method to identify electric charge types with a simple device
,”
Phys. Educ.
50
(
4
),
393
396
(
2015
).
5.
Salvatore
Ganci
, “
An electroscope discriminating the sign of charges
,”
Am. J. Phys.
62
,
474
(
May
1994
).
6.
Frank
Thompson
, “
An electronic electroscope
,”
Phys. Educ.
49
(
1
),
8
20
(
2014
).
7.
Walter
Connolly
,
Gary
Benoit
, and
Mauri
Bould
, “
Apparatus for teaching physics: A new device for studying electric fields
,”
Phys. Teach.
29
,
182
(
March
1991
).
8.
Nahum
Kipnis
, “
Scientific controversies in teaching science: The case of Volta
,”
Sci. Educ.
10
,
3349
(
2001
).
9.
Joost
Mertens
, “
Shocks and sparks: The voltaic pile as a demonstration device
,”
Isis
89
(
2
),
300
311
(
1998
).
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