CHAPTER XXII

UNIPOLAR MACHINES

Homopolar or Acyclic Machines

247. If a conductor, C, revolves around one pole of a stationary
magnet shown as NS in Fig. 215, a continuous voltage is induced
in the conductor by its cutting of the lines of magnetic force of
the pole, 'N, and this voltage can be supplied to an external cir-
cuit, D, by stationary brushes, BI and B^ bearing on the ends
of the revolving conductor, C.

The voltage is:

e = /$ 10-8,

where / is the number of revolutions per second, 4> the magnetic
flux of the magnet, cut by the conductor, C.

FIG. 215.—Diagrammatic illustration of unipolar machine with two high-
speed collectors.
Such a machine is called a unipolar machine, as the conductor
during its rotation traverses the same polarity, in distinction of
bipolar or multipolar machines, in which the conductor during
each revolution passes two or many poles. A more correct name
is homopolar machine, signifying uniformity of polarity, or
acyclic machine, signifying absence of any cyclic change: in all
other electromagnetic machines, the voltage induced in a con-
ductor changes cyclically, and the voltage in each turn is alter-
nating, thus having a frequency, even if the terminal voltage
and current at the commutator* are continuous.
450