Resistor-capacitor (RC) circuits are a popular topic for both theoretical discussion and experimental investigation in introductory physics. This article presents a novel approach to studying such circuits using a piezoelectric buzzer. A capacitor is discharged through a resistor and the buzzer, and the intensity of the sound produced by the buzzer is recorded as a function of time. Here the recordings are made using a smartphone. The voltage supplied to the buzzer, and thus the intensity of the sound it produces, depends on the voltage across the capacitor. As the capacitor discharges exponentially, the sound intensity decreases linearly since the intensity is measured in units of decibels. The linearly decreasing sound intensity can be analyzed to estimate the discharge time constant of the circuit.

1.
A. A.
Moya
, “
Connecting time and frequency in the RC circuit
,”
Phys. Teach.
55
,
228
230
(
April
2017
).
2.
D. P.
Smith
and
P.
van Kampen
, “
A qualitative approach to teaching capacitive circuits
,”
Am. J. Phys.
81
,
389
396
(
May
2013
).
3.
C.
Galeriu
,
C.
Letson
, and
G.
Esper
, “
An Arduino investigation of the RC circuit
,”
Phys. Teach.
53
,
285
288
(
May
2015
).
4.
A.
Parra
,
J.
Ordenes
, and
M. de la
Fuente
, “
Learning abstract physical concepts from experience: Design and use of an RC circuit
,”
Phys. Teach.
56
,
310
312
(
May
2018
).
5.
Uxcell Piezoelectric DC Buzzer, 4 kHz, 3-24V, 85dB, 23x12 mm.
6.
Physics Toolbox Suite, Vieyra Software
, available for iOS and Android, http://www.vieyrasoftware.net.
7.
OpenStax
, “Sound Intensity and Sound Level,” in
College Physics
(
OpenStax CNX
, Aug. 22,
2017
), Chap. 17.3, http://cnx.org/contents/031da8d3-b525-429c-80cf-6c8ed997733a@9.94.
8.
iNVH, Bosch
, available for iOS and Android, https://appcenter.bosch.com/details/-/app/iNVH.
9.
phyphox, RWTH Aachen University, available for iOS and Android, https://phyphox.org.
10.
C. L.
Countryman
, “
The educational impact of smartphone implementation in introductory mechanics laboratories
,”
PERC Proc.
95
98
(
Dec.
2015
).
11.
J.
Kuhn
and
P.
Vogt
, “Smartphones & Co. in Physics Education: Effects of Learning with New Media Experimental Tools in Acoustics,” in
Multidisciplinary Research on Teaching and Learning
, edited by
W.
Schnotz
,
A.
Kauertz
,
H.
Ludwig
,
A.
Müller
, and
J.
Pretsch
(
Palgrave Macmillan
,
London
,
2015
), pp.
253
269
.
12.
A.
Mazzela
and
I.
Testa
, “
An investigation into the effectiveness of smartphone experiments on students’ conceptual knowledge about acceleration
,”
Phys. Educ.
51
(
5
) (
July
2016
).
13.
K.
Hochberg
,
J.
Kuhn
, and
A.
Müller
, “
Using smartphones as experimental tools – Effects on interest, curiosity, and learning in physics education
,”
J. Sci. Educ. Tech.
27
(
5
),
385
403
(
Oct.
2018
), .
14.
T.
Hergemöller
and
D.
Laumann
, “
Smartphone magnification attachment: Microscope or magnifying glass
,”
Phys. Teach.
55
,
361
364
(
Sept.
2017
).
15.
S.
Shakur
and
J.
Kraft
, “
Measuring of Coriolis acceleration with a smartphone
,”
Phys. Teach.
54
,
288
290
(
May
2016
).
16.
P.
Vogt
and
J.
Kuhn
, “
Analyzing simple pendulum phenomena with a smartphone acceleration sensor
,”
Phys. Teach.
50
,
439
440
(
Oct.
2012
).
17.
Y.
Ogawara
,
S.
Bhari
, and
S.
Mahrley
, “
Observation of the magnetic field using a smartphone
,”
Phys. Teach.
55
,
184
185
(
March
2017
).
18.
J.
Kuhn
and
P.
Vogt
, “
Analyzing acoustic phenomena with a smartphone microphone
,”
Phys. Teach.
51
,
118
119
(
Feb.
2013
).
19.
K.
Forinash
and
R. F.
Wisman
, “
Smartphones as portable oscilloscopes for physics labs
,”
Phys. Teach.
50
,
242
243
(
April
2012
).
20.
C. L.
Countryman
, “
Familiarizing students with the basics of a smartphone’s internal sensors
,”
Phys. Teach.
52
,
557
559
(
Dec.
2014
).
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