Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . lying power of 100, when used with a galvanometer of 5000 ohmsresistance? Fig. 122. By Formula (50) S = ^^ = 1QQ__1 = -^T = practice n, is generally 10, 100, or 1000. 148 PRACTICAL ELECTRICITY. These three shunt coils, calculated for any particular gal-vanometer, are arranged in a plug box, called a shunt box,similar to Fig. 125, and by withdrawing the plugs any par-ticular shunt can be quickly connected to the multiplying power is stamped on the box to
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . lying power of 100, when used with a galvanometer of 5000 ohmsresistance? Fig. 122. By Formula (50) S = ^^ = 1QQ__1 = -^T = practice n, is generally 10, 100, or 1000. 148 PRACTICAL ELECTRICITY. These three shunt coils, calculated for any particular gal-vanometer, are arranged in a plug box, called a shunt box,similar to Fig. 125, and by withdrawing the plugs any par-ticular shunt can be quickly connected to the multiplying power is stamped on the box to correspondwith each plug. This shunt box can only be used with thegalvanometer (ammeter or voltmeter), for which it was calcu-lated. Shunt boxes are sometimes called multipliers. Byconnecting a shunt across a galvanometer the resistance ofthe circuit is decreased. If it is desired to keep the resistancethe same as when the galvanometer was not shunted, anotherresistance, known as a compensating resistance, is added in series with the shunted galva-nometer. The value of theresistance to be added equalsn—1. G X n 163. Rheostats.—The usual method of regulatingand controlling the currentrequired for various electri-cal purposes is by inserting,or taking out of a circuit, re-sistance. It will be seen, from Ohms Law, C = |, that if the pressure (E) is constantthe current (C) can readilybe regulated by increasingor decreasing the value ofR ; that is, changing the re-sistance in circuit. An adjustable resistance or any apparatusfor changing the resistance without opening the circuit is calleda rheostat. The function of a rheostat is to absorb electricalenergy, and this energy, which appears as heat, is wasted in-stead of performing any useful work. A rheostat may beconstructed of coils of iron wire, iron plates or strips; car-bon, either pulverized in tubes or in the form of solid rodsor discs; German silver, platinoid, etc., wound on spools ;columns of liquids, as water and mercur
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