. The principles and practice of roentgenological technique . y as the potential or amperage depends onthe nature of the elements and the electrolyte,so the characteristics of a dynamo depend onthe size and shape of its electro-magnets,the size and quantity of wire in the armatureand the speed at which the armature is made torevolve. Motors.—An electric motor is an electro-magnetic machine in which mechanical poweris derived from electric currents, electricalenergy being turned back into mechanicalpower. The action of the electric motor isthe simple converse of that of the dynamo. There are tw
. The principles and practice of roentgenological technique . y as the potential or amperage depends onthe nature of the elements and the electrolyte,so the characteristics of a dynamo depend onthe size and shape of its electro-magnets,the size and quantity of wire in the armatureand the speed at which the armature is made torevolve. Motors.—An electric motor is an electro-magnetic machine in which mechanical poweris derived from electric currents, electricalenergy being turned back into mechanicalpower. The action of the electric motor isthe simple converse of that of the dynamo. There are two kinds of motors, those usedwith the continuous currents and those usedwith the alternating currents. Their construc-tion is similar to that of the dynamo. In themotor the passing of electric current in the ar-mature reacts -on the field magnets resulting in the arnialurc being inilledaround in a turning motion (torque). Thetwo factors of this mechanical rotary powerare torque and speed, the former being pro-portional to the current and the latter to the. Fig. 5.—Commutator and brushes. The brushes, con-sisting of blocks of graphite, carbon or copperstrips, clamped in suitable holders, press againstthe commutator, which consists of copper bars,insulated from each other and connected to thejunction annature coils which are so joined asto make the coil endless. voltage. Since for x-ray work it is importantthat the speed of the motor be maintained atall loads, a compound wound motor of amplecapacit} should be used. If an e. m. f. of 220 volts is impressed acrossthe terminals of a d. c. motor and the currentterminals of a d. c. motor and the currentthrough the motor is 80 amperes, the motorconsumes 6600 watts or K^^. or h. p. Electric Current An electric circuit is the total path traveledby the current: it includes the source, the re-ceptive device in which useful work is per-formed and the conductors connecting thetwo, together with any switches or devices forinaking
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