Time Constant.
(a) When current is first turned into a circuit of considerable
self-induction it is resisted rather by the inductance than by the
resistance. It is governed by the ratio of resistance and self-induction
and this factor represents the time which it takes for the current to
reach a definite fraction of its final strength. This fraction is
(2.7183 - 1)/2.7183 or 0.63. 2.7183 is the base of the Napierian system
of logarithms. Thus if in any circuit we divide the inductance in
henries by the resistance in ohms, the ratio gives the time-constant of
the circuit, or it expresses the time which it will take for the current
to reach 0.63 of its final value.
(b) In a static condenser the time required for the charge to fall to
1/2.7183th part of its original value.
Time Cut-outs.
Cut-outs which automatically cut storage batteries out of the charging
circuit when they are sufficiently charged.
Time-fall.
In a secondary battery the decrease with use of electromotive force
maintained by a primary or secondary battery. As the battery becomes
spent its voltage falls. The conditions of the fall are represented by
its discharging curve. (See Curve, Discharging.)
Time-reaction.
A term in electro-therapeutics; the period of time occupied in the
passage of the effects of an electric current from nerve to muscle.
Time-rise.
In a secondary battery the increase of electromotive force produced
during the charging process. Its rate and conditions are graphically
shown in the charging curve. (See Curve, Charging.)
Tin.
A metal; one of the elements; symbol, Sn; atomic weight, 117.8;
equivalent, 58.9 and 29.5; valency, 2 and 4; specific gravity, 7.3.
It is a conductor of electricity.
Relative resistance, compressed, (Silver = 1) 8.784
Specific resistance at 0° C. (32° F.), 13.21 microhms.
Resistance of a wire at 0° C. (32° F.),
(a) 1 foot long, weighing 1 grain, 1.380 ohms.
(b) 1 foot long, 1/1000 inch thick, 79.47 "
(c) 1 meter long, weighing 1 gram, .9632 "
(d) 1 meter long, 1 millimeter thick, .1682 "
Resistance of a 1 inch cube at 0° C. (32° F.), 5.202 microhms.
Percentage of variation in resistance
per degree C. (1.8° F.), at about 20° C. (68° F.), .0365
Electro-chemical equivalent (hydrogen = .0105), .619 mgs.
.310 "