144 ELEMENTS OF ELECTRICAL ENGINEERING. 



the motor speed is the same as before. The ammeter reading is 

 then observed to be 0.85 ampere, and the electromotive force 

 between the brushes is observed to be 9 1 .6 volts. The resistance 

 (hot) of the armature, as determined by separate measurements, is 

 found to be 0.4 ohm. 



Solution : 



(a) Total power delivered to motor armature to drive the fan 

 = 92.5 volts x 16.4 amp. = 1,517 watts. 



(<) Stray power loss = 91.6 volts x 0.85 amp. 0.4 ohm 

 x (0.85 amp.) 2 = 77.6 watts. 



(c) Armature loss when motor is driving the fan = 0.4 ohm 



X (16.4 amp.) 2 = 107.6 watts. 



(d) Mechanical power delivered to the fan = 1,517 watts 77.6 



watts 107.6 watts = 1,332 watts. 



