Polarization.
(a) The depriving of a voltaic cell of its proper electro-motive force.
Polarization may be due to various causes. The solution may become
exhausted, as in a Smee battery, when the acid is saturated with zinc
and thus a species of polarization follows. But the best definition of
polarization restricts it to the development of counter-electro-motive
force in the battery by the accumulation of hydrogen on the negative
(carbon or copper) plate. To overcome this difficulty many methods are
employed. Oxidizing solutions or solids are used, such as solution of
chromic acid or powdered manganese dioxide, as in the Bunsen and
Leclanché batteries respectively; a roughened surface of platinum black
is used, as in the Smee battery; air is blown through the solution to
carry off the hydrogen, or the plates themselves are moved about in the
solution.
(b) Imparting magnetization to a bar of iron or steel, thus making a
permanent magnet, is the polarization of the steel of which it is made.
Polarization may be permanent, as in steel, or only temporary, as in
soft iron.
(c) The strain upon a dielectric when it separates two oppositely
charged surfaces. The secondary discharge of a Leyden jar, and its
alteration in volume testify to the strain put upon it by charging.
(d) The alteration of arrangement of the molecules of an electrolyte by
a decomposing current. All the molecules are supposed to be arranged
with like ends pointing in the same direction, positive ends facing the
positively-charged plate and negative ends the negatively-charged one.
(e) The production of counter-electro-motive force in a secondary
battery, or in any combination capable of acting as the seat of such
counter-electro-motive force. (See Battery, Secondary--Battery, Gas.)
The same can be found often in organized cellular tissue such as that of
muscles, nerves, or of plants. If a current is passed through this in
one direction, it often establishes a polarization or potential
difference that is susceptible of giving a return current in the
opposite direction when the charging battery is replaced by a conductor.
Polarization Capacity.
A voltaic cell in use becomes polarized by its negative plate
accumulating hydrogen, or other cause. This gradually gives the plate a
positive value, or goes to set up a counter-electro-motive force. The
quantity of electricity required to produce the polarization of a
battery is termed its Polarization Capacity or Capacity of Polarization.
Polarization of the Medium.
The dielectric polarization, q. v., of a dielectric, implying the
arrangement of its molecules in chains or filaments; a term due to
Faraday. He illustrated it by placing filaments of silk in spirits of
turpentine, and introduced into the liquid two conductors. On
electrifying one and grounding (or connecting to earth) the other one,
the silk filaments arranged themselves in a chain or string connecting
the points of the conductors.
Polar Region.
That part of the surface of a magnet whence the internal magnetic lines
emerge into the air. (S. P. Thompson.) As such lines may emerge from
virtually all parts of its surface, the polar regions are indefinite
areas, and are properly restricted to the parts whence the lines emerge
in greatest quantity.
Polar Span.
A proportion of the circle which represents the transverse section of
the armature space between the pole pieces of the field magnet in a
dynamo or motor; it is the proportion which is filled by the faces of
the pole pieces.