Correcting student misconceptions about the cause and prevention of electric shock.
The physics of electric shock is a topic that is addressed in every
general physics text. Invariably, the discussion begins with the effects
in humans of externally induced internal electric currents of various
magnitudes. The texts are fairly good at describing the physiological
effects of these currents, i.e. interference with essential nerve
processes that can produce convulsive muscle action, ventricular
fibrillation, and respiratory arrest. It is made clear that these
internal currents are quite small relative to the currents found in
household electric appliances. Most texts then discuss strategies that
are employed to reduce the danger of electric shock, i.e. polarized plugs, three-wire circuits with the grounding wire and plug, and ground
fault circuit interrupters. However, general physics books
under-emphasize two important things when discussing electrical safety.
These two things are the magnitude of the voltage difference that will
produce a lethal shock and how one can prevent the voltage difference
from being applied across the human body. In an informal, admittedly
unscientific, survey of well-educated acquaintances, it appears that
student misconceptions about electrical safety carry over to adulthood.
Comments such as "it's the current that kills, not the
voltage," a half-truth demonstrating limited knowledge; "the
voltage from a car battery is lethal," a false statement; and
"you have to be grounded to get shocked," another untruth;
coming from respected college graduates in technical fields, make one
wonder if the practical aspects of electrical safety are accurately
presented in the textbooks. In this presentation we will suggest some
ways of correcting these misconceptions, beginning with a complete
definition of electric shock followed by demonstrations illustrating
* Tansil, J.E. Department of Physics & Engineering Physics,
Southeast Missouri State University.