wonderer wrote:

A high school teacher tells the class that pnp stands for positive,
negative, positive and that npn stands for negative, positive,negative.

N actually stands for 'n material', p for 'p material'. The silicon ( typically
) is 'doped' with other elements to make the n and p material which have
different electrical properties. The difference is that in one conduction
through the material takes place using electrons ( n-type ) and in the other by
so-called 'holes' ( p-type ).

http://en.wikipedia.org/wiki/Semicon...#N-type_doping

Graham