. Dental electro-therapeutics. is is aclosed-circuit transformer and a much more efficient machinethan the induction coil. It consists of an iron core, whichis the electro-magnet, a primary coil through which circulatesthe alternating current and a secondary coil which is in themagnetic field and is not wound around the primary butaround a different part of the magnet and receives theinduced current. The E. M. F. induced in the secondarycoil can be regulated by the turns in the coil in ratio to thosein the primary as has been explained elsewhere. Trans-formers for alternating currents are espe
. Dental electro-therapeutics. is is aclosed-circuit transformer and a much more efficient machinethan the induction coil. It consists of an iron core, whichis the electro-magnet, a primary coil through which circulatesthe alternating current and a secondary coil which is in themagnetic field and is not wound around the primary butaround a different part of the magnet and receives theinduced current. The E. M. F. induced in the secondarycoil can be regulated by the turns in the coil in ratio to thosein the primary as has been explained elsewhere. Trans-formers for alternating currents are especially useful forcautery, mouth lamps, hot air, root driers, or syringe. DYNAMO CURRENTS, 91 The principle, as explained, of reducing the volts andincreasing the amperes places the current for these pur-poses entirely in control. By placing a regulating rheostatin the secondary circuit the current which has been trans-formed may be regulated to suit the kind of cautery orlamp or other instrument which it is proposed to use, by. Fig. 31.—Transformer. varying the resistance. The rheostat can be regulated toheat a cautery loop requiring 2 amperes or be adjusted toincrease the current materially to heat a much larger are also used for converting the alter-nating current into high voltage and small amperage forhigh-frequency appliances. They are especially adaptedfor this purpose, for the current being alternating, can be 92 MAGNETIC FIELD, CURRENTS AND BATTERIES used from the main without interrupters. For .r-ray workan alternating current when transformed must be madeunidirectional before it can be used in the tubes. BATTERIES. The construction of galvanic cells, their chemical actionduring the production of current, and the methods of con-necting them to obtain various current strength has alreadybeen described. It has been pointed out that Leclanchecells are the most practical and most lasting form of voltaiccell, because no change takes place within the cell
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