NATIONAL ELECTRIC SAFETY CODE.--See Code, National Electric Safety.
NEGATIVE ELECTRICITY.--See Electricity, Negative.
NON-SYNCHRONOUS GAP.--See Gap, Non-Synchronous.
OHM.--The resistance of a thread of mercury at the temperature of melting ice, 14.4521 grams in mass, of uniform cross-section and a length of 106.300 centimeters.
OHM'S LAW.--The important fixed relation between the electric current, its electromotive force and the resistance of the conductor in which it flows.
OPEN CIRCUIT.--See Circuit, Open.
OPEN CORE TRANSFORMER.--See Transformer, Open Core.
OSCILLATION TRANSFORMER.--See Transformer, Oscillation.
OSCILLATIONS, ELECTRIC.--A current of high frequency that surges through an open or a closed circuit. (1) Electric oscillations may be set up by a spark gap, electric arc or a vacuum tube, when they have not only a high frequency but a high potential, or voltage. (2) When electric waves impinge on an aerial wire they are transformed into electric oscillations of a frequency equal to those which emitted the waves, but since a very small amount of energy is received their potential or voltage is likewise very small.
- Sustained.--Oscillations in which the damping factor is small.
- Damped.--Oscillations in which the damping factor is large.
- Free.--When a condenser discharges through an oscillation circuit, where there is no outside electromotive force acting on it, the oscillations are said to be free.
- Forced.--Oscillations that are made to surge in a circuit whose natural period is different from that of the oscillations set up in it.