The electric energy lost by hysteresis may be reduced by vibrations or
jarring imparted to the iron, thus virtually substituting mechanical for
electrical work.
On account of hysteresis the induced magnetization of a piece of iron or
steel for fields of low intensity will depend on the manner in which the
material has been already magnetized. Let the intensity of field
increase, the magnetization increasing also; then lower the intensity;
the substance tends to and does retain some of its magnetism. Then on
again strengthening the field it will have something to build on, so
that when it attains its former intensity the magnetization will exceed
its former value. For a moderate value of intensity of field the
magnetization can have many values within certain limits.
Synonym--Hysteresis--Hysteresis, Static--Magnetic Friction.
Hysteresis, Viscous.
The gradual increase or creeping up of magnetization when a magnetic
force is applied with absolute steadiness to a piece of iron. It may
last for half an hour or more and amount to several per cent. of the
total magnetization. It is a true magnetic lag.
I.
A symbol sometimes used to indicate current intensity. Thus Ohm's law is
often expressed I = E/R, meaning current intensity is equal to
electro-motive force divided by resistance. C is the more general symbol
for current intensity.
Ideoelectrics or Idioelectrics.
Bodies which become electric by friction. This was the old definition,
the term originating with Gilbert. It was based on a misconception, as
insulation is all that is requisite for frictional electrification,
metals being thus electrified if held by insulating handles. The term is
virtually obsolete; as far as it means anything it means insulating
substances such as scaling wax, sulphur, or glass.
Idle Coils.
Coils in a dynamo, in which coils no electro-motive force is being
generated. This may occur when, as a coil breaks connection with the
commutator brush, it enters a region void of lines of magnetic force, or
where the lines are tangential to the circle of the armature.
Idiostatic Method.
A method of using the absolute or attracted disc electrometer. (See
Electrometer, Absolute.) The suspended disc and guard ring are kept at
the same potential, which is that of one of the points whose potential
difference is to be determined; the lower fixed disc is connected to the
other of the points whose potential difference is to be determined. Then
we have the formula