. Practical wireless telegraphy; a complete text book for students of radio communication . the remainder of this circuit, a current flows in the external circuitfrom antimony to bismuth. If the junction is cooled below temperature of the restof the circuit, current will flow in the opposite direction. There are a rmmber ofother metals which when joined and heated will produce a direct E. M. F. underchange of temperature, notably copper and iron, which are frequently used as a thermo-junction. 50. Induction Coil.—^We have shown how an alternating current can beraised to a pressure of severalth
. Practical wireless telegraphy; a complete text book for students of radio communication . the remainder of this circuit, a current flows in the external circuitfrom antimony to bismuth. If the junction is cooled below temperature of the restof the circuit, current will flow in the opposite direction. There are a rmmber ofother metals which when joined and heated will produce a direct E. M. F. underchange of temperature, notably copper and iron, which are frequently used as a thermo-junction. 50. Induction Coil.—^We have shown how an alternating current can beraised to a pressure of severalthousand volts by means of the alter-nating current transformer. In asomewhat similar manner, a directcurrent of low voltage can be changedto an alternating current of manythousand volts by an apparatusknown as an induction coil. Fig. 57 is a diagrammatic sketch ofan induction coil. P is the primarywinding and S the secondary is a piece of spring brass fitted witha soft iron button that may be attractedby the core C. A is an adjustable thumbscrew, platinum tipped, which makes. Fig. 54—^Hot Wire Ammeter with Internal Shunt. contact at C^, closing the circuit of the battery through winding P. In practice sole-noid S is wound about C. When the battery circuit is closed at K, the core becomes saturated with magnetismand attracts the armature B. B being drawn to the end of the iron core, the flow ofcurrent is broken at C^. Since the current is now cut off from P the magnetic fielddisappears and the tension of the spring causes the circuit to be closed again at C^.This process is repeated continuously, resulting in from 30 to 100 breaks per second. ELECTROMAGNETIC INDUCTION. 47 MILLIAMMETER \e35jj[ o The coil P generally has 1 or 2 layers of coarse insulated copper wire of differentsizes (the size varying with the current) which are thoroughly insulated fromthe core C. Winding P is covered with aninsulating tube which supports winding secondary winding may have many
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Keywords: ., bookcentury1900, bookdecade1910, booksubjecttelegra, bookyear1917
