. Elements of electric traction for motormen and others . the ammeter indicating thecurrent that passed through the circuit— 96 volts . . 10| amps. 48 „ . . 5 „ 24 „ ... 2L „ thus indicating that with half the pressure half the current, and withone quarter the pressure one quarter the current, or vice experiment was now varied— (2) To show the actual effect of varying resistance. A constant pressure of 24 volts was applied to the terminals ofthe water resistance. The plates in the first instance were 18 inchesapart. In the second instance they were placed 9 inches apart,namely, half
. Elements of electric traction for motormen and others . the ammeter indicating thecurrent that passed through the circuit— 96 volts . . 10| amps. 48 „ . . 5 „ 24 „ ... 2L „ thus indicating that with half the pressure half the current, and withone quarter the pressure one quarter the current, or vice experiment was now varied— (2) To show the actual effect of varying resistance. A constant pressure of 24 volts was applied to the terminals ofthe water resistance. The plates in the first instance were 18 inchesapart. In the second instance they were placed 9 inches apart,namely, half the original distance, the resistance in consequencebeing approximately halved. In the third instance they were placed PRINCIPLES OF ELECTRICITY 27 41 inches apart, the resistance then being approximately one foUowinf? results were obtained :— Plates 18 inches apart9 41 2*37 thus indicating roughly that reducing the resistance to one-half itsoriginal value caused the current to increase to approximately twice BATTERY. Fig. 6. its original value, and with one quarter the resistance the currentwas increased to approximately four times its value, or vice may now be stated that— 1 volt pressure is required to drive 1 amp. through a resistanceof 1 ohm ; therefore 2 volts pressure will be required to drive 2 amps, through aresistance of 1 ohm; 3 volts pressure will be required to drive 3 amps, through aresistance of 1 ohm; and so on ; and it also follows that— 3 volts pressure will be required to drive 1 amp. through a resistance of 3 has now been seen not only how the current varies with 28 ELEMENTS OF ELECTRIC TRACTION varying pressure and resistance in a general way, but also how itvaries in a more exact way, such that calculations can be law is generally written thus— (1) ^ = 1 (2) CR = E; or (3) R = ^ where E is equal to the number of volts pressure,E „ „ „ ohms resistance, C „ „ „ amperes. These are a
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