In many states, electric fences are used to prevent animals from leaving a designated area, for example for grazing. They are quite well known by most students and can therefore serve as daily-life examples of electric circuits. Besides helping to grasp the ideas of Kirchhoff’s laws for voltages and currents in circuits according to loop and junction rules, they can also serve as introduction to the topic of conduction of electricity by humans and respective effects (in contrast to electric fences, the latter can also be studied experimentally in the classroom). Here we provide background information on the circuit diagrams of electrical fences that also explains the so-called Brainiac YouTube videos on the topic. While electric fences are designed not to be dangerous to humans or animals due to the short duration of the electrical pulses, students and teachers are strongly discouraged from attempting to replicate the scenes enacted in the video.

1.
M.
Vollmer
and
K. P.
Möllmann
, “
Music through the skin – Simple demonstration of human electrical conductivity
,”
Phys. Educ.
51
,
034002
(
2016
).
3.
Dan
MacIsaac
, “
WebSights: The Brainiacs and the electric fence from YouTube
,”
Phys. Teach.
47
,
396
(
Sept.
2009
).
4.
United States Department of Agriculture
, “
Electric Fencing for Serious Grazers
” (
National Resources Conservation Service
,
Columbia, MO
), see http://www.mo.nrcs.usda.gov or directly https://prod.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs144p2_010636.pdf.
5.
R.
Grisso
,
M.
Alley
,
D.
Holshouser
, and
W.
Thomason
,
Precision Farming Tools: Soil Electrical Conductivity
, Virginia Cooperative Extension Publication
442
508
(
College of Agriculture and Life Sciences, Virginia Polytechnic Institute and State University
,
2009
).
6.
R. N.
Barbosa
and
C.
Overstreet
,
What Is Soil Electrical Conductivity?
Louisiana State University Agricultural Center Pub. 3185, 2/11
, http://www.lsuagcenter.com/nr/rdonlyres/e57e82a0-3b99-4dee-99b5-cf2ad7c43aef/77101/pub3185whatissoilelectricalconductivityhighres.pdf.
7.
Sand is usually drier than clay and resistances vary in wide ranges.5,6 Frozen soil with ice is usually a very bad conductor. Order of magnitude estimates may use soil conductivities of, e.g., 5 mS/m for sand and 100 mS/m for clay. Soil resistivity is inversely proportional, and we find for sand about 200 Ωm and for clay 10 Ωm, respectively.
8.
In practice, seasonal changes with dry periods may lead to appreciable changes in the top soil conductivity. Therefore, the ground stakes of electric fences should be deep enough in soil layers that still carry moisture although the top is very dry.
9.
G.
Biegelmeier
, “
New Experiments with Regard to Basic Safety Measures for Electrical Equipment and Installations
,” in
Proceedings of the First International Symposium on Electrical Shock Safety Criteria
, edited by
J. E.
Bridges
, et al.
(
Pergamon Press
,
1985
), pp.
161
172
.
10.
R.
Feynman
,
The Feynman Lectures on Physics
, Vol.
II
(
Addison-Wesley
,
1963
), Ch. 22.
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