An elementary book on electricity and magnetism and their applications . quare centimeters. 4. It is desired to determine the permeability of a sample of round test piece 4 centimeters in diameter and 60 centimeters longis formed into a ring about which are wound 1000 turns of wire. Theinductance is then measured and found to be henrys. What isthe permeability? 225. Reactance. We have already seen (Chapter XII) thatan alternating current changes constantly, so that it never hasa steady value,and the effectof inductance istherefore felt byit all the result is, aswas shown i
An elementary book on electricity and magnetism and their applications . quare centimeters. 4. It is desired to determine the permeability of a sample of round test piece 4 centimeters in diameter and 60 centimeters longis formed into a ring about which are wound 1000 turns of wire. Theinductance is then measured and found to be henrys. What isthe permeability? 225. Reactance. We have already seen (Chapter XII) thatan alternating current changes constantly, so that it never hasa steady value,and the effectof inductance istherefore felt byit all the result is, aswas shown in sec-tion 219, that ina circuit havinginductance an al-ternating currentis always retarded a certain amount behind the alternatingvoltage which sets it up. In short, inductance makes an alter-nating current lag behind its voltage (Fig. 225). This sameretardation makes the maximum value of the current smallerthan it would be were there no inductance. This effect of inductance in decreasing the amount of alter-nating current which flows in a circuit depends, as we have. Fig. 225. — Current lags behind voltage in inductivecircuit. 328 ELECTRICITY AND MAGNETISM seen, upon the magnetic effect which the different parts of thecircuit have on each other, and also upon the frequency of thecurrent. For example, if we have a certain eoil whose inductance is 1 henry,and use it on an a-c. circuit whose frequency is 60 cycles, we have acertain magnetic effect. But if we change the frequency to 120 cycles,we double our frequency; that is, we double the rapidity with whichthe current changes in value from instant to instant, and therebydouble the speed with which the magnetic flux set up by that currentcuts through the conductors in the coil. This doubling of the rate atwhich the flux changes doubles the of self-induction, whichmeans that twice the impressed electromotive force is required at120 cycles to maintain a given current through the coil as is requiredto maintain that same c
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmagnetism, bookyear19
