PROBLEMS. 483 



143. How many grams of SO 3 are removed from the electrolyte 

 during the discharge of a 120 ampere-hour storage cell ? Ans. 

 359 grams, half of which is absorbed by each electrode. 



144. The electromotive force of a storage cell is observed to be 

 2.05 volts on open-circuit and the electromotive force is observed 

 to fall suddenly to 1.95 volts when a current of 50 amperes is 

 taken from the cell. What is the resistance of the cell ? Ans. 

 0.002 ohm. 



145. A storage battery consisting of 61 cells has an internal 

 resistance of 0.03 ohm. The battery delivers a current of 100 

 amperes at no volts to lighting mains when the resistance of 

 the rheostat, R, shown in Fig. 146, Chapter VIII., is 0.12 ohm. 

 (a) What is the voltage between the mains when half of the lamps 

 are suddenly turned off? (&) Calculate the resistance required 

 in the rheostat, R, to bring the voltage across the lighting mains 

 back to 1 10 volts. Ans. (a) 117.5 volts; (6) 0.27 ohm. 



146. The lamps in Fig. 150, Chapter VIII., require a constant 

 electromotive force of no volts and the current demanded by 

 the elevator motor varies from zero to 150 amperes with an 

 average value of 25 amperes. The booster, M, is provided with 

 the two opposing field windings, 5 and S f . (The winding, S f , may 

 be assumed to be connected to the constant-voltage mains in 

 parallel with the lamps for the sake of simplicity.) The constant 

 field excitation due to S' is equal to $n, and the opposing field ex- 

 citation due to 5 is 372 when the current flowing through 5 is 25 

 amperes ; where n is the ampere -turns on the field of M required 

 to produce 10 volts between the brushes of M. The storage 

 battery consists of 5 1 cells with a minimum voltage of 96.9 volts 

 (1.9 volts per cell) and a maximum voltage of 122.4 volts (2.4 

 volts per cell). The minimum occurs, of course, when the battery 

 is nearly discharged and the elevator motor is taking its maximum 

 current of 1 50 amperes, and the maximum occurs when the battery 

 is nearly charged and the elevator motor is taking no current at 

 all. Find the current delivered through J/and 5 to the elevator 

 motor and battery : (a) when the battery is nearly discharged and 



