Many of the old demonstrations in electricity and magnetism can be performed more effectively and with greater visual appeal by using newly available neodymium magnets and color LEDs. For this reason several demonstrations, commonly used for teaching electromagnetic induction and Lenz’s law, have received renewed attention in recent years. In particular strong neodymium magnets have been used in several new demonstrations and experiments to help students learn the subtleties of eddy currents and magnetic braking. Here we describe several demonstrations that use a strong neodymium magnet, a coil, and a few LEDs to teach students in introductory physics the fundamentals of electromagnetic induction. More importantly the addition of LEDs provides a visual demonstration of Lenz’s law, with which many students have some difficulty. The demonstrations described here are quite simple to construct, fun to do, and visually appealing; they may be used either in the laboratory or in the classroom.

1.
J. L.
Ferguson
, “
A supersensitive LED Faraday’s law demonstration
,”
Phys. Teach.
39
,
444
(
Oct.
2001
).
2.
A.
Singh
,
Y. N.
Mohapatra
, and
S.
Kumar
, “
Electromagnetic induction and damping: Quantitative experiments using a PC interface
,”
Am. J. Phys
.
70
,
424
427
(
April
2002
).
3.
L. T.
Wood
,
R. M.
Rottmann
, and
R.
Barrera
, “
Faraday’s law, Lenz’s law, and conservation of energy
,”
Am. J. Phys
.
72
,
376
(
March
2004
).
4.
S. M.
Cohen
, “
Active learning in lectures introducing magnetic induction
,”
Am. J. Phys
.
73
,
284
(
March
2005
).
5.
Gren
Ireson
and
John
Twidle
, “
Magnetic braking revisited: Activities for the undergraduate laboratory
,”
Eur. J. Phys.
29
,
745
751
(
2008
).
6.
G.
Donoso
,
C. L.
Ladera
, and
P.
Martın
, “
Magnet fall inside a conductive pipe: Motion and the role of the pipe wall thickness
,”
Eur. J. Phys.
30
,
855
869
(
2009
).
7.
G.
Donoso
,
C. L.
Ladera
, and
P.
Martin
, “
Damped fall of magnets inside a conducting pipe
,”
Am. J. Phys.
79
,
193
200
(
Feb.
2011
).
8.
J. A.
Molina-Bolivar
and
A. J.
Abella-Palacios
A laboratory activity on the eddy current brake
,”
Eur. J. Phys.
33
,
697
707
(
2012
).
9.
D.
Wood
and
J.
Sebranek
, “
Electromagnetic induction with neodymium magnets
,”
Phys. Teach
.
51
,
344
(
Sept.
2013
).
10.
S. R.
Pathare
,
S.
Huli
,
R.
Lahane
, and
S.
Sawant
, “
Low-cost timer to measure the terminal velocity of a magnet falling through a conducting pipe
,”
Phys. Teach
.
52
,
160
(
March
2014
).
11.
B.
Irvine
,
M.
Kemnetz
,
A.
Gangopadhyaya
, and
T.
Ruubel
, “
Magnet traveling through a conducting pipe: A variation on the analytical approach
,”
Am. J. Phys
.
82
,
273
(
April
2014
).
12.
J.
Priest
and
B.
Wade
, “
Lenz’s law experiment
,”
Phys. Teach
.
30
,
106
108
(
Feb.
1992
).
13.
C. A.
Sawicki
, “
Lenz’s law: Feel the force
,”
Phys. Teach
.
34
,
38
39
(
Jan.
1996
).
14.
W.
Dindorf
, “
Lenz’s law in the kitchen
,”
Phys. Teach
.
37
,
268
(
May
1999
).
15.
D. T.
Ivanov
, “
Another way to demonstrate Lenz’s law
,”
Phys. Teach.
38
,
48
(
Jan.
2000
).
16.
C. G.
Zhang
and
S. F.
Hu
, “
Another way to demonstrate Lenz’s law
,”
Phys. Teach.
40
,
249
(
April
2002
).
17.
M. J.
Ruiz
, “
Lenz’s law magic trick
,”
Phys. Teach.
44
,
96
(
Feb.
2006
).
18.
J. A.
Pelesko
,
M.
Cesky
, and
S.
Huertas
, “
Lenz’s law and dimensional analysis
,”
Am. J. Phys
.
73
,
37
39
(
Jan.
2005
).
19.
M. K.
Roy
,
M. K.
Harbola
, and
H. C.
Verma
, “
Demonstration of Lenz’s law: Analysis of a magnet falling through a conducting pipe
,”
Am. J. Phys
.
75
,
728
730
(
Aug.
2007
).
20.
Neodymium cylindrical magnets are available from Applied Magnets (http://www.magnets4less.com) and other retailers.
21.
Clear Polycarbonate Pipe, 7/8-in ID x 1-in OD x 1/16-in wall, 36-in L, available from Amazon.com.
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