Indicator.
(a) An apparatus for indicating the condition of a distant element, such
as the water level in a reservoir, the temperature of a drying room or
cold storage room or any other datum. They are of the most varied
constructions.
(b) The receiving instrument in a telegraph system is sometimes thus
termed.
Indicator, Circuit.
A galvanometer used to show when a circuit is active, and to give an
approximate measurement of its strength. It is a less accurate and
delicate form of instrument than the laboratory appliance.
Inductance.
The property of a circuit in virtue of which it exercises induction and
develops lines of force. It is defined variously. As clear and
satisfactory a definition as any is the following, due to Sumpner and
Fleming: Inductance is the ratio between the total induction through a
circuit to the current producing it. "Thus taking a simple helix of five
turns carrying a current of two units, and assuming that 1,000 lines of
force passed through the central turn, of which owing to leakage only
900 thread the next adjacent on each side, and again only 800 through
the end turns, there would be 800 + 900 + 1000 + 900 + 800, or 4,400
linkages of lines with the wire, and this being with 2 units of current,
there would be 2,200 linkages with unit current, and consequently the
self-inductance of the helix would be 2,200 centimetres." (Kennelly.)
Inductance, as regards its dimensions is usually reduced to a length,
hence the last word of the preceding quotation.
The practical unit of inductance is termed the henry, from Prof. Joseph
Henry; the secohm, or the quad or quadrant. The latter alludes to the
quadrant of the earth, the value in length of the unit in question.
[Transcriber's note: (L (di/dt) = V). A current changing at the rate of
one ampere per second through a one henry inductance produces one volt.
A sinusoidal current produces a voltage 90 degrees ahead of the current,
a cosine (the derivative of sine is cosine). One volt across one henry
causes the current to increase at one ampere per second.]
Induction, Coefficient of Self.
The coefficient of self-induction of a circuit is the quantity of
induction passing through it per unit current in it. If a given circuit
is carrying a varying current it is producing a varying quantity of
magnetic induction through itself. The quantity of induction through the
circuit due to its current is generally proportional to its current. The
quantity for unit current is the coefficient of self-induction.
(Emtage.)
Induction, Cross.
The induction of magnetic lines of force in a dynamo armature core by
the current passing around such armature. These lines in a symmetrical
two pole machine are at right angles to the lines of force which would
normally extend across the space between the two magnet poles. The joint
magnetizing effect of the field and of the cross induction produces a
distorted field between the poles .
Synonym--Cross-magnetizing Effect.