Field, Drag of.
When a conductor is moved through a field so that a current is generated
in it, the field due to that current blends with the other field and
with its lines of force, distorting the field, thereby producing a drag
upon its own motion, because lines of force always tend to straighten
themselves, and the straightening would represent cessation of motion in
the conductor. This tendency to straightening therefore resists the
motion of the conductor and acts a drag upon it.
Field of Force.
The space in the neighborhood of an attracting or repelling mass or
system. Of electric fields of force there are two kinds, the
Electrostatic and the Magnetic Fields of Force, both of which may be
referred to. A field of force may be laid out as a collection of
elements termed Lines of Force, and this nomenclature is universally
adopted in electricity. The system of lines may be so constructed that
(a) the work done in passing from one equipotential surface to the next
is always the same; or (b) the lines of force are so laid out and
distributed that at a place in which unit force is exercised there is a
single line of force passing through the corresponding equipotential
surface in each unit of area of that surface. The latter is the
universal method in describing electric fields. It secures the following
advantages:--First: The potential at any point in the field of space
surrounding the attracting or repelling mass or masses is found by
determining on which imaginary equipotential surface that point lies.
Second: If unit length of a line of force cross n equipotential
surfaces, the mean force along that line along the course of that part
of it is equal to n units; for the difference of potential of the two
ends of that part of the line of force = n; it is also equal to F s (F
= force), because it represents numerically a certain amount of work;
but s = I, whence n = F. Third: The force at any part of the field
corresponds to the extent to which the lines of force are crowded
together; and thence it may be determined by the number of lines of
force which pass through a unit of area of the corresponding
equipotential surface, that area being so chosen as to comprise the
point in question. (Daniell.)
Field of Force, Electrostatic.
The field established by the attracting, repelling and stressing
influence of an electrostatically charged body. It is often termed an
Electrostatic Field. (See Field of Force.)