The Montgomery advertiser., 1901-09-19

ADVERTISER
 Such a distribution closely initiates the the old pan-cake wndinis nnd Fave s the magnetic field more gradually. than is possible with the singie-tooth style; nut by adoption of the toother, slotted or s.iron-cIadH armature, the machine illus trated in figure @ and originally rated at $ K. ", became cspa6ls of supplying sor wound armature coils, that can be in- sulated and inspected. then laid In place on the core, readily removed tn case or hooked or T-shaped tooth has disappeared and straight ones adopted. Though in troducing some undesirable features, the real gain is on the side of facilitated re-
 An inquiry into the theory of aiternat- ing currents brings the average reader to sudden halt. The principle of the direct Ohm's law seem to be left far behind. He may well pause; unless he is well grounded in mathematics, further prog. equipped, he will find approximate formu- lac, involved physical considerations; symbolic methods of representation and introdaetion of imaginary 0sc.sI or eomPie5 of the knowledge cannot be depreciated, for most rignaliy in this department of en- gineering have the manufacturers been dependent upon theoretical considera- tions. Some facts. however. concerning law of current flow can be easily ex- An Alternating current is one which somewhat gradually rises to its full or maxmium value then falls to zero. and in reversed direction attains a second equal value and returns to zero, thus hundred or so such cycles take place dur ing one second does not alter this pro. cess of current growth. decay. reversal and repetition. If single coil be placed on drum core and rotated once in bipolar field all these changes will be ex- perienced and can be illustrated by ref conductor of the loop in the position of the mark. where they are momentarily. It Is cutting no lines of force ,and pass ing to the 90 degree Roint 1t wiil nave .,a cut from 90 to 1s0 degrees. the rate of cutting will have fallen of until zero condition is again reached, continuing the rotation. other pole at similar rates. If the dotted circle be cut open and rolled out into a straight line, as in the right hand DOT be more clearly shown, As the result of the conductor cutting these lines of force an c. m. f. will be induced, the instan- taneous value of which will be dependent upon the particular rate of the cutting. At o. 1S0 and 360 degrees the cutting Is zero, and there Is no e: m. f. generated; at 90 degrees the rate will be a maximum, but is about to decline; at the lsO mark change In direction of e. m. f. takes place, and a similar curve below the axis rep resents an equal succt ssion Of values. For the upper area Is denoted as positive and the lower as negative. this diction having r, ference to the direction of the e. m. f. Negative values are just as useful as positive in the same sense that tempera- lures recorded below zero on ther- mometer are as legitimate as those above. If the generator has a multipolar field, the same curve would repro sent the vary ing e. m. f.. and the $50 degrees would represent. not a complete revolution of the mature, but a move ment from one north pole to the next north.
 If the external circuit Is closed, cur rent will flow. but will paEs through zero and maximum values periodically, imitat- Ing the e. m. f. or current Is evidently some average between these extremes. It can be shown mathematically that the energy Of any wave motion varies as the square of the amplitude. In this curve the amplitude is the radius of the circle; 1t can be called united or l, taking the two extreme values the square of zero Is average square between these values will be one-half; the length of one side of such a square will be the square root of one-half. or T. That is. an alternating current generator which supplies a max imum potential of 100 volts would indi- cate but 70 on a voltmeter, or an am- meter that showed an alternating current of amperes would at instants be passing 10.
 The effect of alternating currents in the actual working circuit demands for assigned in short article. but briefly 1t can be stated that if the load be incan- descent lamps the operation is closely identified with the case of direct cur rents. Line resistance and losses and va riations of voltage can be closely call culated by application .ofs Ohm's law. If the load be motors or any apparatus in volving coils of wire and iron cores, the case Is radically different in that resist ances other than ohmic are present In many cases the actual resistance of the rent being determined by the other fac tors. If an alternating current flows through coil any inoiosed iron will ex- perience t ,5 simlar & &fnsnges & Q. maSne.s;i % rnar; upon the current that produced them and generate a counter electromotive force: in this respect, the case is analogous to that of the direct current motors. for the wires conveying the current experience a c. m. Did space permit, It could be shown that the maximum values of the riod or 90 degrees behind those of the current; this c. c. m. f. Is technically de- noted as the "reactance. If right tri- angle be drawn and the bace denoted as the resistance. tho altitude as the re- 'impedance. fhe principle of ohm's law can De used tO CdICuldte the current by placing the instantaneous e. m, f. In the numerator and the impedance in the denonlinator. Often, as in the case of kicking coils and primaries of trans formers when no lamps are lighted, the base line is very short and the altitude very high The same triangle can be used to represent electromotive forces; the base can indicate the e. m. f. neces- sary to overcome the ohmic resistance, the altitude that necessity to overcome the reactance and the hypotenuse the po- tential necessary to drive the particular current against both these opposing
 ITO Be Continued.I