We present a simple experiment to measure the magnetic dipole moment of a magnet using two identical magnets and spring dynamometers. The experiment illustrates the concept of a dipole field, as well as the interaction between two magnetic dipoles. The validity of the magnetic dipole approximation is discussed. The experiment also makes it possible to obtain the remanent magnetization of rare earth magnets.

1.
R. A.
Lufburrow
, “
Inverse-square law experiment
,”
Am. J. Phys.
31
(
1
),
60
62
(
1963
).
2.
A.
Romer
, “
Magnetic repulsion: An introductory experiment
,”
Am. J. Phys.
41
(
12
),
1332
1336
(
1973
).
3.
S.
Defrancesco
and
V.
Zaneth
, “
Experiments on magnetic repulsion
,”
Am. J. Phys.
51
(
11
),
1023
1025
(
1983
).
4.
D. P.
Shelton
and
M. E.
Kettner
, “
Potential energy of interaction for two magnetic pucks
,”
Am. J. Phys.
56
(
1
),
51
52
(
1988
).
5.
E.
Levin
, “
Magnetic dipole moment measurement
,”
Am. J. Phys.
52
(
3
),
248
250
(
1984
).
6.
J.
Bisquert
,
E.
Hurtado
,
S.
Mafe
, and
J.
Pina
, “
Oscillations of a dipole in a magnetic field: An experiment
,”
Am. J. Phys.
58
(
9
),
838
843
(
1990
).
7.
H. G.
Lukefahr
, “
Magnetic dipole interactions on an air track
,”
Am. J. Phys.
60
(
12
),
1134
1136
(
1992
).
8.
D. J.
Griffiths
,
Introduction to Electrodynamics
, 2nd ed. (
Prentice-Hall
, Englewood Cliffs, NJ,
1989
), Chap. 6, p.
247
.
9.

See Ref. 8, Chap. 5, p. 238.

10.
D.
Jiles
,
Introduction to Magnetism and Magnetic Materials
(
Chapman and Hall
, London,
1991
), Chap. 4, p.
72
.
11.

See Ref. 10, Chap. 13, p. 318.

12.
S.
Earnshaw
, “
On the nature of the molecular forces which regulate the constitution of the luminferous ether
,”
Trans. Cambridge Philos. Soc.
7
,
97
112
(
1842
).
13.
G. L.
Squires
,
Practical Physics
(
Cambridge U. P.
, Cambridge, MA,
2001
), Chap. 4, p.
32
.
14.
J. R.
Reitz
and
F. J.
Milford
,
Foundations of Electromagnetic Theory
(
Addison-Wesley
, New York,
1969
), Chap. 8, p.
169
.
AAPT members receive access to the American Journal of Physics and The Physics Teacher as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.