The traditional analysis of RC circuits with constant resistance fails to adequately account for the charging characteristics of a capacitor in series with a lamp. We find that a simple model for the changing resistance of the lamp provides a good fit to the time-varying current in the circuit. This experiment can readily be performed in an introductory physics laboratory.

1.
D. C.
Giancoli
,
Physics for Scientists and Engineers
, 3rd ed. (
Prentice Hall
, Upper Saddle River, NJ,
2000
), pp.
669
673
.
2.
D.
Halliday
,
R.
Resnick
, and
J.
Walker
,
Fundamentals of Physics
, 6th ed. (
Wiley
, New York,
2001
), pp.
648
651
.
3.
D. W.
Wilson
and
C. A.
Hernandez
,
Physics Laboratory Experiments
, 6th ed. (
Houghton Mifflin
, Boston, MA,
2005
), pp.
325
350
.
4.
D.
Sokoloff
,
R.
Thornton
, and
P.
Laws
,
RealTime Physics
(
Wiley
, New York,
2004
), Module 3, Electric Circuits.
5.
E.
Hellen
, “
Verifying the diode-capacitor circuit voltage decay
,”
Am. J. Phys.
71
(
8
),
797
800
(
2003
).
6.
G.
Brizuela
and
A.
Juan
, “
Planck’s constant determination using a light bulb
,”
Am. J. Phys.
64
(
6
),
819
821
(
1996
).
7.
B.
Prasad
and
R.
Mascarenhas
, “
A laboratory experiment on the application of Stefan’s law to tungsten filament electric lamps
,”
Am. J. Phys.
46
(
4
),
420
423
(
1978
).
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