Point, Null.
A nodal point in electrical resonators; a point where in a system of
waves or oscillations, there is rest, the zero of motion being the
resultant of oppositely directed and equal forces. In electrical
resonators it is to be sought for in a point symmetrically situated,
with reference to the spark gap, or in a pair of points, which pair is
symmetrically placed.
The null point in resonators is found by connecting a lead from one of
the secondary terminals of an induction coil to different parts of the
resonator. The null point is one where the connection does not give rise
to any sparks between the micrometer knobs or spark gap, or where the
sparks are of diminished size.
The whole is exactly comparable to loops and nodes in a vibrating string
or in a Chladni plate as described in treatises on sound and acoustics.
(See Resonance, Electrical--Resonator, Electrical.)
Synonym--Nodal Point.
Point Poles.
Magnet poles that are virtually points, or of no magnitude. A long thin
magnet with little leakage except close to the ends may be supposed to
have point poles within itself a short distance back from the ends.
Points, Consequent.
In a magnet with consequent poles, the points where such poles are
situated.
Points, Corresponding.
In bound electrostatic charges the points of equal charges of opposite
potentials; the points at opposite extremities of electrostatic lines of
force. This definition implies that the bound charges shall be on equal
facing areas of conductors, as otherwise the spread or concentration of
the lines of force would necessitate the use of areas of size
proportionate to the spreading or concentrating of the lines of force.
At the same time it may figuratively be applied to these cases, the
penetration of the surface by a single line of force including the area
fixed by its relation to the surrounding lines.
Points, Isoelectric.
In electro-therapeutics, points of equal potential in a circuit.