. An elementary manual of radiotelegraphy and radiotelephony for students and operators . g in a straight infinitely longconductor, magnetic flux is distributed in circular lines round thatconductor in the space outside and inside the wire. If a magnetic pole, that is the end of a very long thin magnet,is held in the field of the current it will tend to rotate round thewire, being urged by a force proportional to the strength of thepole and to the magnetic force at the point where it is proving this are described in every book on physics. If, however, a short magnet is laid on
. An elementary manual of radiotelegraphy and radiotelephony for students and operators . g in a straight infinitely longconductor, magnetic flux is distributed in circular lines round thatconductor in the space outside and inside the wire. If a magnetic pole, that is the end of a very long thin magnet,is held in the field of the current it will tend to rotate round thewire, being urged by a force proportional to the strength of thepole and to the magnetic force at the point where it is proving this are described in every book on physics. If, however, a short magnet is laid on a disc of card, the cardbeing suspended so as to be free to rotate in a plane perpendicularto the current, but the magnet not free to move on the card, therewill be no rotation of the latter (see Fig. 2). When this experiment is carefully considered, it will be foundto prove that the magnetic force (H) at any point near the longstraiglit current must be inversely as the perpendicular distanceof the point from the current, and further au analysis shows that WAVES 131. it is proportional to twici ilio current aii<l inversely us the liisttiuei. If, then, wo consider a single circulur lino of magnetic Ihix of nulius r, its length is 27r7, and the magnetic force uU along 20it has a value —, where Cr is the current in the wire. 20The product 27rr x — = 47rO is called the line intf(jnxl ofthe magnetic force along thatline, and we see that it isinilcpeudent of the radius,and therefore of the form ofthe })ath. Accordingly, theline integral of the magneticforce along any closed lineembracing a current is equalto 47r times the total currentflowing through that closedline. Applying then Max-wells principle, we see thatif in any dielectric the electric strain (D) is changing with time, its rate of change -j- ^^ j) m^i. tiplied by \tt, gives us the line integral of the magnetic force dueto it along a boundary-line perpendicular to the direction of theelectric strain
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Keywords: ., bookcentury1900, bookdecade1910, booksubjecttelegra, bookyear1916
