Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

RE: Shockers...



Dwight,
In the 1990 edition of Trinklein's Modern Physics (misnamed HS book), in
section 20.19, there is a circuit for a device that lights a neon bulb when
a switch is opened.  It consists of an iron core coil in series with a
parallel combination of the neon bulb and a spst switch.  When the switch is
closed, current flows through the coil,b ut the neon bulb is an open circuit,
so no current flows through it.  When the switch is opened, the sudden change
in the established magnetic field in the coil produces a large counter emf
(which is the sum of the emfs of each of the coils in series, so it's
quite large) which is enough to flash the neon bulb for an instant.  The
circuit in the book is basically an adaptation of this.  The covers are 
isolated from each other and comprise the terminals of the neon bulb,
while the battery and coil are hidden inside the book.  By using a large coil
of many turns (old dc motor armature) you can create a nasty but brief 
surge from cover to cover.

Regards,
JFK