SKIN EFFECT.--See Resistance, High Frequency.
SOFT TUBE.--A vacuum tube in which the vacuum is low, that is, it is not highly exhausted.
SPACE CHARGE EFFECT.--The electric field intensity due to the pressure of the negative electrons in the space between the filament and plate which at last equals and neutralizes that due to the positive potential of the plate so that there is no force acting on the electrons near the filament.
SPARK.--See Discharge.
SPARK COIL.--See Coil, Induction.
SPARK DISCHARGE.--See Spark, Electric.
SPARK FREQUENCY.--See Frequency, Spark.
SPARK GAP.--(1) A spark gap, without the hyphen, means the apparatus in which sparks take place; it is also called a spark discharger. (2) Spark-gap, with the hyphen, means the air-gap between the opposed faces of the electrodes in which sparks are produced.
- Plain.--A spark gap with fixed electrodes.
- Rotary.--A spark gap with a pair of fixed electrodes and a number of electrodes mounted on a rotating element.
- Quenched.--A spark gap formed of a number of metal plates placed closely together and insulated from each other.
SPIDER WEB INDUCTANCE COIL.--See Coil, Spider Web Inductance.