c. In electricity, the word "ground" is used to refer to a connection made directly
to the earth or to a conductor connected to the earth.
(1) Because of its atomic structure, the earth contains an almost limitless
quantity of neutral atoms. This makes it possible for the earth to give up electrons
without appreciably affecting the neutrality of the ground and, thus, to neutralize a large
(2) Likewise, the earth can absorb excessive electrons to neutralize a large
negative charge. If a body carrying a positive charge is connected to the ground,
electrons flowing to it from the ground will neutralize it. If a negatively charged body is
connected to the ground, electrons flowing from it into the ground will neutralize the
(3) Because of its ability to neutralize any possible charge the earth is
considered to be at zero potential. Thus, ground potential always equals zero potential.
This is an extremely important factor in the shock-proofing of x-ray machines and other
NATURE Of AN ELECTRIC CURRENT
a. The term electric current refers to a flow of electrons through a conductor. An
electric current, consisting of moving electrons, must have kinetic energy. The flow of
(1) To produce an electrical effect, some valence orbit electrons (called
"free" electrons) must be removed from the atom and made to move from one atom to
the next in a particular direction. In a material such as copper, there are many free
electrons. This makes it an excellent conductor. The loosely bound valence orbit
electrons of copper atoms can be put into motion and made to move progressively from
one atom to the next atom through the wire. There is no continuous flow of electrons
and a single electron will not go far--in effect, it may be considered as a series of jumps
of an electron to the atom ahead.
(2) In order to have a flow of current, there must be a path, or conductor, in
which electrons can move. This conductor must be in the form of a closed loop that
provides a continuous path for the flow of current. This path, or closed loop, is a circuit.
No significant electric current will flow in a nonconductor (such as glass, rubber, and
mica) because the electrons in these substances are tightly bound to their respective
atoms (there are few free electrons).