CHAPTER III 

 POWER AND WORK 



1. 50 amperes at 110 volts give how many horse-power? 

 Required the current at 500 volts to give the same horse-power; 

 also at 1000 volts. (2 min.) 



2. At 8 cents per kilowatt-hour how much will it cost, per week 

 of 60 hours, to run a motor having an average load of 4 horse- 

 power and an average efficiency of 80%? (3 min.) 



3. A 20-candle-power tungsten incandescent lamp takes 1.3 

 watts per candle-power; a common price for this purpose is 10 

 cents per kw.-hour; at this price, what will it cost to run 8 ] mps 

 for three hours? (2 min.) 



4. What must be the horse-power delivered by an engine to 

 run by belt a generator feeding 500 J-ampere lamps at 110 volts? 

 Four volts are lost in the line, the efficiency of the generator is 

 90% and the loss in the belt is 1%. (4 min.) 



5. A motor at 1000 feet from the generator requires 20 amperes 

 at 500 volts. The wire used is a No. 6. Required the e.m.f. at 

 the generator and the per cent of the volts lost; also the power 

 lost and the per cent of the power lost. (5 min.) 



6. Same as problem 5 but using No. 4 wire. (5 min.) 



7. What will be the loss in pressure and in watts in trans- 

 mitting 100 horse-power at 500 volts through a No. 0000 wire, 

 taking the resistance for 30 C. as 0.05086 ohms per 1000 feet, and 

 the distance being one mile? What are the respective per cents of 

 e.m.f. and power lost? (5 min.) 



8. A 220- volt motor with 80% efficiency gives 8.94 horse- 

 power, is 1000 feet distant from the generator and is wired with 

 a No. 6 wire; how many horse-power are lost in the circuit, and 

 at what voltage must the generator run in order that the motor 

 may have its proper pressure? What per cent of the delivered 

 e.m.f. and power is lost in the transmission? (6 min.) 



9. A test with a Prony brake shows that a certain motor is 

 giving 132,000 foot-pounds per minute. The input is 7.46 amperes 

 at 500 volts. What is the efficiency? (2 min.) 



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