MasteringPhysics: Assignment #7-Google Chrome @ https://session.masteringphysics

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MasteringPhysics: Assignment #7-Google Chrome @ https://session.masteringphysics.com/myct/itemView?assignmentProblemID-62562681 Engineering Physics Spring 2016 Help | Close Assignment #7 A DC Motor Resources Y previous 2 of 16 next» A DC Motor Part C Compute the emf & A shunt-wound DC motor with the field coils and rotor connected in parallel (see the figure) (Figure 1) operates from a 100 V DC power line. The resista Rf , is 239 . The resistance of the rotor, Rr, is 5.80 When the motor is running, the rotor develops an emf . The motor draws a current of 4.70 A from the line. Friction losses amount to 45.0 W nce of the field windings Submit Hints My Answers Give Up Review Part Figure 1 of 1 Part D Compute the rate of development of thermal energy in the field windings Express your answer in watts. dc , R Pth,windings Submit Hints My Answers Give Up Review Part Part E Compute the rate Pth,rotor of development of thermal energy in the rotor Express your answer in watts. I'm Cortana. Ask me anything 1:32 AM 4/26/2016

Explanation / Answer

part a )

If = 100/239 = 0.4184 A

part b )

rotor current = Ir = Itotal - If

Ir = 4.7 - 0.4184 = 4.2816 A

part c )

V = e + Ir*Rr

e = V -Ir*Rr

e = 100 - (4.2816 * 5.8) = 75.1668 V

part d )

Pf = If^2*Rf = 41.84 W

part e )

Pr = Ir^2*Rr = 106.32567 W

part f)

Pin = 100 * 4.7 = 470 W

part g )

efficiency = Poutput/Pin = (470 - 106.32567 - 41.84 - 45)/470

e = 0.589

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