288 THE DIRECT-CURRENT MOTOR 



7. A dynamo gives 900 terminal volts on open circuit at 

 850 r.p.m. Find the maximum possible speed when placed 

 as a motor on a 300-volt circuit with the same magnet 

 strength as before. 284 r.p.m. 



8. A motor with an internal resistance of 0'03 ohm is 

 connected to a 100-volt circuit. Find the speed when there 

 is a load of 5,400 inch-pounds on the shaft. 924 r.p.m. 



9. What is the maximum possible horse-power of a motor 

 with an internal resistance of 0'8 ohm when running on a 

 100-volt circuit ? 4-2. 



10. Find the induction factor of a motor that will run at 

 480 r.p.m. on a tension of 500 volts, and give a torque of 

 3,280 inch-pounds. The internal resistance is 0'8 ohm. 



58-5. 



11. Find the induction factor of a motor that will give 12 

 horse-power at 1,500 r.p.m. on a tension of 100 volts. The 

 resistance is O'l ohm. 3'6. 



12. A four-pole street railway motor has a series-con- 

 nected armature with 624 surface conductors and a resistance 

 of 1'2 ohm. Find the number of useful lines per pole 

 required to run at 800 r.p.m. with 1,200 inch-pounds of 

 torque on a 500-volt line. 2-83 x 10 6 . 



13. Check the results of Problems 11 and 12 by showing 

 that the line-watts is equal to the sum of the heat-watts and 

 the mechanical watts. 



14. A main shaft has to run at 240 r.p.m. with a load of 

 4,600 inch-pounds, and is driven by a motor with a 10-inch 

 pulley belted to a 48-inch pulley. The friction of the motor, 

 &c., amounts to 500 inch-pounds on the motor shaft. The 

 tension of the line is 150 volts, and the resistance of the 

 motor 0-07 ohm. Find the induction factor. 7'28. 



15. Cheek the result of Problem 14 for input and output 

 of energy. 



16. A four-pole motor which has its armature con- 

 nected in series and 480 surface conductors, raises an un- 

 balanced lift weighing 1,500 Ibs. at 240 f.p.m. The rope 



