Electro-motive Force, Counter.
A current going through a circuit often has not only true or ohmic
resistance to overcome, but meets an opposing E. M. F. This is termed
counter-electro-motive force. It is often treated in calculations as
resistance, and is termed spurious resistance. It may be a part of the
impedance of a circuit.
In a primary battery hydrogen accumulating on the negative plate
develops counter E. M. F. In the voltaic arc the differential heating of
the two carbons does the same. The storage battery is changed by a
current passing in the opposite direction to its own natural current;
the polarity of such a battery is counter E. M. F.
Electro-motive Force, Unit.
Unit electro-motive force is that which is created in a conductor moving
through a magnetic field at such a rate as to cut one unit line of force
per second. It is that which must be maintained in a circuit of unit
resistance to maintain a current of unit quantity therein. It is that
which must be maintained between the ends of a conductor in order that
unit current may do unit work in a second.
Electro-motive Intensity.
The force acting upon a unit charge of electricity. The mean force is
equal to the difference of potential between two points within the field
situated one centimeter apart, such distance being measured along the
lines of force. The term is due to J. Clerk Maxwell.
Electro-motive Series.
Arrangement of the metals and carbon in series with the most
electro-positive at one end, and electronegative at the other end. The
following are examples for different exciting liquids:
Dilute Sulphuric Dilute Hydrochloric Caustic Potassium
Acid Acid. Potash. Sulphide.
Zinc Zinc Zinc Zinc
Cadmium Cadmium Tin Copper
Tin Tin Cadmium Cadmium
Lead Lead Antimony Tin
Iron Iron Lead Silver
Nickel Copper Bismuth Antimony
Bismuth Bismuth Iron Lead
Antimony Nickel Copper Bismuth
Copper Silver Nickel Nickel
Silver Antimony Silver Iron
Gold
Platinum
Carbon
In each series the upper metal is the positive, dissolved or attacked
element.