In the cut A B is the graduated potentiometer wire through which a
current is passed in the direction of the arrow. E is the battery under
trial, placed in opposition to the other current, with a galvanometer
next it. Under the conditions shown, if the galvanometer showed no
deflection, the E. M. F. of the battery would be to the E. M. F. between
the ends of the potentiometer wire, 1 . . . . .10, as 1.5 the distance
between the points of connection, A and D of the battery circuit, is to
10, the full length of the potentiometer wire.
Poundal.
The British unit of force; the force which acting on a mass of one pound
for one second produces an acceleration of one foot.
[Transcriber's note: The force which acting on a mass of one pound
produces an acceleration of ONE FOOT PER SECOND PER SECOND.]
Power. Activity;
the rate of activity, of doing work, or of expending energy. The
practical unit of electric power is the volt-ampere or watt, equal to
1E7 ergs per second. The kilowatt, one thousand watts or volt-amperes,
is a frequently adopted unit.
Power, Electric.
As energy is the capacity for doing work, electric energy is represented
by electricity in motion against a resistance. This possesses a species
of inertia, which gives it a species of kinetic energy. To produce such
motion, electro- motive force is required. The product of E. M. F. by
quantity is therefore electric energy. (See Energy, Electric.)
Generally the rate of energy or power is used. Its dimensions are
( ( (M^.5)*(L^.5) ) / T ) * ( ( (M^.5) *(L^1.5) )/( T^2) )
(intensity or current rate) * (electro-motive force or potential)
= (M * (L^2) ) / (T^3),
which are the dimensions of rate of work or activity. The practical unit
of electric rate of energy or activity is the volt-ampere or watt. By
Ohm's law, q. v., we have C = E/R (C = current; E = potential difference
or electro-motive force; R = resistance.) The watt by definition = C*E.
By substitution from Ohm's formula we deduce for it the following
values: ((C^2) * R) and ((E^2) /R). From these three expressions the
relations of electric energy to E.M.F., Resistance, and Current can be
deduced.
Power of Periodic Current.
The rate of energy in a circuit carrying a periodic current. In such a
circuit the electro-motive force travels in advance of the current it
produces on the circuit. Consequently at phases or intervals where,
owing to the alternations of the current, the current is at zero, the
electro-motive force may be quite high. At any time the energy rate is
the product of the electro-motive force by the amperage. To obtain the
power or average rate of energy, the product of the maximum
electro-motive force and maximum current must be divided by two and
multiplied by the cosine of the angle of lag, which is the angle
expressing the difference of phase.
[Transcriber's note; The voltage phase will lead if the load is
inductive. The current phase will lead if the load is capacitive.
Capacitors or inductors may be introduced into power lines to correct
the phase offset introduced by customer loads.]