ooo AT&T; LTE 10:00 PM a session masteringphysics.com T o 17%, D Exercise 27.47
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ooo AT&T; LTE 10:00 PM a session masteringphysics.com T o 17%, D Exercise 27.47 MasteringPhysics Exercise 27.47 In a shunt-wound dc motor with the field coils and rotor connected in parallel (see the figure 120V E, R a Tap image to zoom the resistance Rf of the field coils is Rs 110 2 and the resistance Rr of the rotor is R 5.5 2.When a potential 20 V is applied to the brushes and the difference of V motor is running at full speed delivering mechanical power, the current supplied to it is 4.85 A. Part A What is the current in the field coils?Explanation / Answer
The field current is: V/R = 120/110 = 1.091 A
The only other current flowing is the rotor current: Ir = Itot - Ifld
Ir = 4.85 - .1.091 = 3.76
The emf: The rotor current multiplied by the rotor resistance is the difference between the line voltage and the counter emf:
emf = Vline - Irotor*Rrotor = 120 - 3.76*5.5 = 99.32 V
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