to the flow of electric current and so have learned considerable
about the theory of electricity.
We have said that it is the movement of electrons in an
electrical circuit that is a flow of electric current.
Right here we want to impress on your mind the terrific
speed at which electrons react on each other. If we had a wire
stretched from New York to San Francisco, and there was a
disturbance of electrons at one end, the electrons at the other
end would feel the effect of this disturbance in 1/60th of a
second, for electrical disturbances travel at the rate of approximately
186,000 miles per second.
Now we have talked about disturbing the electron and you
have naturally wondered just how electrons are put into motion.
You are familiar with the ordinary electric battery, the
kind that supplies the power for some radio receiving sets,
door bells, etc. In the battery are various chemicals--we'll
learn just what they are later--which are capable of acting on
Fig. 3
each other in such a way that some electrons of which they are
formed, become separated from their atoms and gather on one
of the battery terminals.
One terminal of a cell or battery is called positive. The
other terminal is called negative. These terminals were so called
just to give the terminals a name. You will therefore understand
that the words “positive” and “negative” are only “names”
which will identify a certain “end,” “terminal,” “place,” or in
fact “anything.” If the ends of a copper rod are connected by a
wire to the two terminals of an electric battery to form a complete
circuit as illustrated in Fig. 4 the free electrons will move
slowly from the negative terminal of the battery along the wire
towards the copper rod. They leave the copper rod at the end
marked + and travel down the wire to the positive terminal of
the battery. In other words, as fast as the electrons leave the
+ end of the copper rod, they are supplied at the – end.
This is strictly true, however, before the discoveries were
made that led to the electron theory, physicists believed that
